Monthly Archives: June 2022

Why dispersion is better than distribution: fabric ducts vs. metal and flex ducts

How to make air on a submarine: 2 lessons on air quality

Ok, I’ve never been inside a submerged submarine, but I’ve toured part of a docked submarine and I think it takes a special kind of person to live in those cramped conditions for months at a time.  Combining this with the fact that unlike a normal ship, there is no natural atmosphere from which to take air to breathe, makes submariners a very special breed!  

I learned about the different ways submarines make oxygen and remove carbon dioxide from the ship’s atmosphere in this interesting video.  While you may think this information irrelevant because a) you don’t live underwater, and b) no one but the US government could afford such fancy equipment, there are several things to take away for our own home use.  

First of all, the submarine is highly compartmentalized, not only for function, but for safety.  This means that if the ship were to be struck by a torpedo in one compartment and started to take on water, it’s likely that by sealing off that compartment, the ship could continue on its mission or at least get to a port for repairs.  The number of these individual compartments require a specialized air monitoring and distribution to each compartment.  There are no “open concept” submarines!  The name of the monitoring system is CAMS, or Compartment Atmosphere Monitoring System. It tells the sailors the air quality (percentage O2, CO2, CO, and other contaminants like refrigerant) in each compartment.  You may have an open-concept floorplan in your home, but it’s likely that you have individual rooms wherever privacy is needed: for your bedroom, bathroom and office.  So, atmosphere monitoring can show you whether your ventilation is working well or if there is a contaminant like radon that is poisoning a certain area of your home.  Here are some ways to add atmosphere monitoring to your home.  In order to control your atmosphere, you first have to know what is in it!

• AirThings makes several types of monitors that you can read locally or remotely

• Kaiterra makes attractive LaserEggs that not only show what’s in your air; they look like they are part of modern decor.

• Awair also has a sleek, modern design to their home indoor sensor, which has the “most accurate airflow design on the ma

• PurpleAir makes an indoor sensor and 2 outdoor sensors, and offers the opportunity to upload your local outdoor air quality to a nationwide map!  

Second, because ability to breathe is such an important function on a submarine, there are redundant systems: two different ways to make oxygen, and two different ways to remove carbon dioxide.  Even if one system is working well 99% of the time, the sailors practice by testing the other system regularly to ensure its function and their knowledge and ability to use it.  Redundancy is good to have in your home too.  If your main way of ventilation is via the central air, what happens if your power goes out?  You can throw open the windows, but that plan does not work well if you haven’t checked whether windows are painted shut, or if they have clean, well-fitted screens to keep bugs out.  A “backup plan” is only as good as you prepare it to be, and emergencies like power outages rarely have advance notice!  Similarly, if your main way of getting fresh air is via a cracked window, do you know what to do in case there’s a wildfire in your area or the mobile exterminating truck starts spraying toxic chemicals down your street?  Of course, you will close the window, but having an air purifier or HEPA filter or extra MERV-13 furnace filters on hand make it more comfortable for you and your family until the air is clear again.  Check out our post on natural disasters and how to prepare for good air quality during and after them. 

Natural disasters: How to prepare for them and protect your air quality

In certain sections of the US and the world, seasonal weather can turn dangerous in a matter of days, hours or even minutes.  We want to help you be ready for these situations by planning ahead.  Having the proper plans and supplies in place is reassuring during a stressful time! Before any storm is on the horizon, you can:

• Purchase appropriate insurance.
• Take a household inventory of major household items and valuables with photos and model numbers. 
• Store important documents in fire- and water-proof boxes.

Then, you can have a basic survival kit on hand at home, to get you through several different types of emergencies. Here is an example kit from ready.gov:

• Water (one gallon per person per day for several days, for drinking and sanitation)
• Food (at least a several-day supply of non-perishable food)
• Battery-powered or hand crank radio and a NOAA Weather Radio with tone alert
• Flashlight
• First aid kit
• Extra batteries
• Whistle (to signal for help)
• Dust mask (to help filter contaminated air)
• Plastic sheeting and duct tape (to shelter in place)
• Moist towelettes, garbage bags and plastic ties (for personal sanitation)
• Wrench or pliers (to turn off utilities)
• Manual can opener (for food)
• Local maps
• Cell phone with chargers and a backup battery

Wildfires.  You may not live in fire-prone areas, but as we’ve seen in the past few years, even a small wildfire can affect thousands of homes outside the burn zone with deadly smoke.  In our post about wildfires, we outline some basic things you can do to prevent wildfire smoke from making your home inhabitable:

• Seal doors and windows with weatherstripping, caulk and door sweeps.  
• Find out how to adjust your HVAC system accordingly: you’ll want to close the fresh air intake and change over to recirculation, no matter whether you have central AC, a window air conditioner or portable air conditioner.
• Purchase extra MERV 13 or higher filters for your HVAC system, to be used on poor air quality days.
• If you live in an apartment building or condo with little control over the HVAC, consider purchasing vent filter material so you can place them in the vents into your space. Carbon vent filter material will neutralize many VOCs as well.
• Purchase a HEPA air cleaner (non-ozone producing type) and be sure to have an extra filter or two on hand. 
• Keep a stash of N95 respirator masks on hand.    
• Don’t cook during a wildfire emergency, because cooking indoors increases small particulates and vapors in the air, and you won’t want to turn on your stove exhaust, as that will draw polluted outdoor air into the house.  Try to use just the canned food you have on hand.
• Check your local air quality and receive updates from airnow.gov . Fire and smoke maps are available under the heading fire.airnow.gov . 

Hurricanes:  Although a number of hurricanes have formed in May and December, hurricane season for the Atlantic is June 1 through November 30.  The intensity and frequency of storms is predicted to be above normal in 2022, for the seventh consecutive year (economist.com).  It’s all the more reason to be ready in case one of these mega-storms comes your way.  

Here’s some interesting facts about how hurricanes affect air quality:

• Whether you stay in your home or evacuate, it’s good to be aware that the reaction of local oil and petrochemical refineries to the storm is critical.  According to a report published by environmentalintegrity.org, industrial plants in the Houston area waited too long to shut down after receiving warnings about Hurricane Harvey.  This resulted in 8.3 million pounds of unpermitted air pollution being released into the air, including dangerous plumes of cancer-causing benzene, “much of it triggered by flooding-related mishaps like electrical outages, equipment malfunctions, and the failure of floating roof tanks.”  These releases subsequently caused 3 of the worst days of high ozone levels in the same area.
• You may not have accurate air quality information during and after the storm.  The same report confirmed that “part of the TCEQ’s (Texas Commission on Environmental Quality) disaster planning strategy included shutting down air monitors to protect them from damage. Approximately 75 percent of the stationary air monitoring equipment from the Houston, Corpus Christi, and Beaumont-Port Arthur areas was temporarily removed in preparation for Hurricane Harvey, according to state officials.  These heavily industrialized areas are home to many of the largest sources of air pollution in the United States. “
• The intense winds of hurricanes can pick up dust and broadcast it in large areas, including coarse grit sand down to fine grains of 2.5 microns and smaller. (nbcnews.com) These fine and ultra-fine particles are super-dangerous to lungs and our whole bodies, because they can lodge deep in the lungs and even transfer into the bloodstream.  You can see the effects of hurricane winds and what they pick up when viewing road signs after the storm: if they are still standing, many road signs have a “sand-blasted” effect that is not just from water but also from the dust picked up by the winds.  
• During a hurricane, power outages cause humidity levels to climb in your home, encouraging the growth of mold and dust mites, two major indoor allergens. (Allergy and Asthma Care of Florida)
• After a hurricane, excess standing water can promote the growth of grasses and weeds, at a time when homeowners, business owners and governments are not prepared to cut them.  This can worsen allergies for many.  (Allergy and Asthma Care of Florida)  Trees that are stripped bare during the hurricane can also regrow their leaves and even bloom again, because the stress of the hurricane changes the plants’ hormone levels.  (morningagclips.com)  That can mean almost double the pollen in one year!
• Roof damage and water penetrating the home’s exterior will allow mold to grow in places that may remain undetected for months or years.  

Preparing for riding out a hurricane in your home is similar to a wildfire (see tips above). You’ll want to have the appropriate filters, masks, canned food and water on hand, and also know how to prevent fresh air intake if the air quality outside gets too bad.  You’ll want to have portable fans on hand in order to circulate air in your home, because air circulation can prevent mold growth.  Being able to run a generator if the power goes out can also improve your comfort by having access to frozen food supplies, light, power to cook with, and fans to circulate air so you can sleep!  If you do run a generator, check out our recommendations on running it safely in our post Power Outages and Air Quality. 

Tornadoes:  Being intensely windy storms, severe thunderstorms and the tornadoes they can spawn bring many of the risks of hurricanes.  The wind, rain, and potential damage are all there, most times with even more intensity in a tornado.  According to the University of Miami, “While both types of storms are capable of producing destructive winds, tornadoes can become stronger than hurricanes. The most intense winds in a tornado can exceed 300 miles per hour, while the strongest known Atlantic hurricane contained winds of 190 miles per hour. “  This means that the amount of dust and debris a tornado can pick up is many times more than a hurricane per area.  Tornadoes an hurricanes are both storms of wind and rain.  The reason a tornado is “visible” to the human eye, as well as radar systems, is because of the massive amount of dust, debris and hail that it contains!

The other problem with tornadoes is their lack of warning.  Many times residents, businesses and industry have 10 minutes or less to take shelter, let alone prepare their dwelling or workplace for the possibility of severe damage.  Therefore, it’s critical to have supplies and a plan to execute in case of one.

• Of course, the most important thing is getting to shelter.  Your tornado shelter needs to be a place which is always accessible and well-known to your family or co-workers.  Whether or not your home has a purpose-built safe room, be sure to have the above mentioned supplies of the disaster kit, plus warm clothing and bedding, because weather conditions can change drastically with such a storm.
• If you know that a tornado is in your area and you have time before sheltering, you can:
  • Turn off gas and water to your home, to avoid fire or flooding. 
  • Close fresh air intake into your home and close all windows.  According to weather.gov, “It is now believed that a solid structure (no windows or doors open) has a better chance of escaping major damage.”

Flooding.  Meteorologists cannot always predict the amount and path of water in storms, and building in floodplains is a common practice in some areas.  According to a 2021 study, “damaging floods are increasing in severity, duration and frequency, owing to changes in climate, land use, infrastructure and population demographics.”  From 2000 to 2015, approximately 58 to 86 million people moved to flood-prone regions, they found, which translates to a roughly 20% increase in the population exposed to floods. If your area even has a minimal chance of flooding (see this page to decode the flood zone category of your property, or search FEMA’s Flood Map Service Center by your address), then you should prepare for one.  Here are some ways to do it:

• A flash flood is “A flood caused by heavy or excessive rainfall in a short period of time, generally less than 6 hours.”(weather.gov)  Warnings issued for flash floods are serious because the flooding can be very unpredictable.  Do not attempt to drive in areas where flash flooding is predicted, and never through floodwaters.
• You should attempt to move yourself, and if possible anything of value to you, to higher ground.  For example, in your home you can move smaller valuables to upper stories or the attic.  In your car, drive away from the flooded area to higher ground.  
• Moving back into a flooded home requires quick remediation; mold can start growth within 48 hours so it’s important to get all waterlogged furniture and carpeting removed, and surfaces like floors and walls dried out as soon as possible.  If your area sustains major flooding, professional help can be difficult to secure, but don’t give up!  
• Air quality in your home depends on how extensive the flooding is and long water remains, but even the humidity of a few inches of water can start to affect those who are prone to asthma.  Therefore those who have respiratory issues should not try to help clear a flooded house. 
• If you’re working on your own (without professional remediation), you’ll want to:
  • Use respiratory protection and appropriate clothing, shoes and gloves
  • Remove all drywall and insulation below the floodline, as well as 2-4 feet up the wall.  This is because the drywall wicks up water, and the insulation behind it will be wet also.  The goal is to get the studs and all of the wall cavity dry.
  • Use as many fans as possible to increase air circulation for drying. 
  • Clear particulates from the air using a large HEPA filter such as our Cleanroom WindPRO 650, or if you don’t have the budget, make a Box Fan Air Cleaner. 
• Flooded neighborhoods can increase in mosquitoes, fleas, ticks and mites very quickly after a storm, so be sure to wear insect repellent and change clothing at least daily if you’re encountering insect problems. 

Summer road trips: How to breathe easy wherever you go!

The great American tradition of taking a road trip during the summer is still popular after the COVID-19 pandemic, although fuel and lodging prices may cause some to shorten their range or length of stay (skift.com).  Of those staying at home instead of traveling, 33% were concerned about their own safety and the safety of others.  At HypoAir, we want everyone to enjoy their summer, and with some precautions, a road trip can be part of it!

Make sure to pack the devices that keep you safe at home:

• TotalClean is an odorless cleaner made with iodine that is safe to clean any surface, as well as deodorize the air around it!  Use it on door handles and hotel room sinks and fixtures, 
• Germ Defender and Air Angel will clean the air and surfaces in your hotel room quickly and quietly.  Simply plug them in when you arrive (Germ Defender works great in small spaces like the bathroom, and Air Angel in larger spaces like the bedroom), and return after dinner to a cleaner room.  If you don’t have a car adapter for your Air Angel, make sure to order one so you can sanitize your car everyday while you drive!
• Disposable gloves are great to have “on hand” for high-touch areas like gas pumps.  Although they are designed to be disposed of after use, if you are running low on them, a study has shown that applying hand sanitizer to the gloves does not reduce their effectiveness or increase puncturability. 
• Hand sanitizer, of course!  It’s helpful to have a pump bottle in the car so that you don’t have to fumble with a cap or handle the bottle with hands that may be contaminated.  Hand-sanitizing wipes are great for your purse, baby bag or luggage.  You can check out our post on hand sanitizers to find some that are non-toxic.
• Masks:  Bring a good supply so that you won’t be stressed about losing or re-using a masks.  See our post about face masks here.
• Snacks and drinks: you can minimize time spent to find the right snacks, eat healthier, and spend less in general by buying snacks in grocery stores before you go on your trip instead of in convenience stores along the way. (aarp.com)
• When checking your car’s fluids and systems, consider replacing the cabin air filter and vacuuming out the car so that you’ll have fresh air to breathe for all those hours on the road. 

Stopping to eat at local restaurants is part of the fun of visiting a new area.  You may opt to choose outdoor dining, which is generally safer than indoor because of the fresh air ventilation all around you, but if the restaurant doesn’t have an outdoor option, you can try a couple different strategies to avoid viruses and germs in the air:

• Request to be seated close to the door, which naturally provides ventilation as customers go in and out. 
• Use a different kind of “mask”.  Normally when masked customers are seated at a table, they unmask to eat and have conversation, which somewhat defeats the purpose of wearing a mask into the restaurant!  Instead, you can try “nasal filters”.  There are many types and most are very comfortable and undetectable, meaning you can easily wear them, be protected, wear lipstick, and let your smile say it all!  It’s best to get a few pairs and practice wearing them at home and in public before you go on your trip, to be mindful of nose breathing over mouth breathing.  The first nasal filters were invented in Thomas Carence from Kansas City, Missouri in 1901 as a solution to hay fever (news.crunchbase.com), and then, but since the pandemic the styles and sources have multiplied. The upside of wearing these filters is that they are generally more comfortable than masks, so you’re apt to wear them all day and protect yourself from other contaminants like pollen, dust and air pollution.  Here are some styles you can try:
  • O2 Nose Filters come in 4 different sizes and the webpage has helpful videos on why and how to wear them. 10 filter sets are $14.99.
  • First Defense Nasal Screens use a safe adhesive to apply the screens, for those who are wary of sticking an object into their nostrils.  A one-week supply (7 sets) is $9.98.
  • Rhinix.com is mainly marketed towards seasonal allergy sufferers but can capture any allergen the size of pollen grains (about 15 microns).  These filters were developed in 2011 by a Danish medical student and ship from Denmark.  While driving through different sections of the country, you may encounter allergens your body does not like, therefore, these are great protection that are easy to wear all day long!

Even if it’s humid outside, indoor air conditioned environments can be very drying to your nose and lungs.  This can cause you to be susceptible to allergens, viruses and bacteria.   FEND Nasal Spray works in a different way than masks.  It hydrates your nasal passages with a blend of water, calcium and sodium to enable your own respiratory system to keep producing the mucus that protects you.  The makers of FEND recommend use at least every 6 hours by spraying it into the air and breathing the mist deeply through your nostrils. 

Hotel rooms, as we mentioned, can be of particular concern during peak travel season and when you’re not sure how the hotel sanitizes.  We gave a lot of advice in our post “Hypoallergenic Hotel Suites”; here are the highlights:

• You can find a Pure Room (that has been cleaned to specific requirements) here, or search for “allergy-free hotel (destination city)” for a variety of listings.
• If you want to find out how these rooms are cleaned, instead of calling a nationwide 1-800 booking line, try to call the local hotel directly and speak to someone who is head over housekeeping or knowledgable in their practices.
• Think about bringing your own towels, sheets or sleep sack, and staying in a hotel with laundry facilities.
• Don’t be afraid to ask for a different room if you sense that yours was not cleaned well or has a musty odor (quite common in more humid areas). 

Big cities and highways can be some of the worst areas for air pollution, and sometimes it’s necessary to drive through them.  In our post about air quality inside your car, we’ve described the technique for allowing the least amount of that pollution into the cabin where you’re breathing.

• Consider signing up for a free trial or subscription at Breezometer.com in order to plan driving routes with better air quality.
• When encountering heavy pollution, it is best to close the windows, set the ventilation to “recirc” and set the fan on low.  Also, using the air conditioning will lower indoor contaminants.
• The recirc setting should only be used for a short time, because the concentration of carbon dioxide from passengers’ breathing starts to become high.

If you’re “roughing it”--whether that means using an RV or tent– campfires are fun to make for cooking food or just marshmallows and s’mores.   Building a fire outdoors will create fine and ultra-fine particulates, however, that you should avoid breathing in by staying upwind of the smoke.  Here are some other tips from clevelandclinic.org for making a safer campfire time:

• Use only untreated wood, because burning treated wood can release toxic vapors.
• If possible, avoid using manufactured logs to start the fire; here are some tips to starting a campfire (#3 on list)
• Don’t use gasoline or lighter fluid to start or maintain a campfire; not only are they dangerous to those around the fire, they can release toxins into the air. 
• Only burn on calm days (winds less than 20 miles per hour) and where there are not burn bans in effect because of forest fire danger.

Our country and roads offer some great getaways and we hope you will take advantage of them safely!

Our New Healthy Home WishList

Sometimes, after hearing about many customers’ problems with their existing homes (problems with attics, basements, crawlspaces, inadequate ventilation, too much humidity, poor location, etc.), we just want to do a positive post on what our dream house would look like!  What if you could build a new home in any location to make it as healthy as possible?  Where would it be and how would it be constructed?  There are lots of methods and designs to choose from, so don’t get overwhelmed, just relish the possibilities! 

1. Size.  Homes have always been a showcase of the owner’s tastes, abilities, and wealth.  Most homes are built today with the current owner’s needs and plans in mind: if a couple plans to expand their family, they will try to incorporate extra rooms for more children, for example.  Size is therefore a function of meeting current and future needs, budget, and space to build on.  There is no “best size” for a healthy home, as long as all spaces are ventilated and properly maintained.  

• Don’t over-size it!  The problem with “oversizing” a home is that unused rooms still need to be conditioned and maintained, using energy.  Closing off ventilation registers in unused rooms is not good for the HVAC system or the air quality in the room.  Unused rooms should have circulating fans left on and some sort of ventilation connection with the rest of the house (door vent grilles or transom windows are great for this purpose if you want to close the door).   This article looks at the ideal house size in which to raise a family.
• Once you build a home and love where you live, it’s hard to conceive of moving in the future just because you grow out of  space.  Look at incorporating expansion into the plans at the beginning.  Here are 4 plans that make expansion easier by incorporating it into the plan.  This allows you to build “just right” and expand when needed.
• Try to find an architect who is known for indoor air quality.  It is better to use their skills in design to build a home of the right size, small or large, than to work with an architect who designs beautiful homes but does not design for air quality.

2. Foundation: We have to protect our homes from moisture coming up from the ground, and without encapsulation, crawlspaces just do not offer the best protection.  A properly waterproofed slab or basement affords better protection than a crawlspace.  Although it may not look like it, concrete is porous.  You’ll need a water barrier below it (slab) and around it (basement).  If you build in an area with very moist soil or active springs, it is important to have the proper drainage around  and under your basement.  Having a finished basement requires no water coming in, so that the air is not becoming humidified.  The temperature of basements, because they are in contact with the cool earth, is cooler, and cooler air can hold less moisture (its relative humidity will get higher).  Higher relative humidity causes everything in the basement to become more moist, risking mold growth.  So, even if you have a properly waterproofed basement, you may need to use a dehumidifier or small heater to keep the relative humidity at the proper level.  Remember that a finished basement will need to be included in the ventilation system!  
3. Attic:  Unconditioned attics can serve as a thermal “buffer” between your home and the outdoors, but they require proper ventilation, which can be difficult to get right even with the proper products (soffit vents, baffles and ridge vents).  For this reason, we recommend no attics (with the rooms’ ceilings extending to the rooflines) or conditioned attics (the thermal envelope still resides at the roofline and the attic space may be finished or unfinished).  Conditioned attics are an extension of the home below, and if HVAC equipment or any storage is located there, it is not subjected to extreme heat, cold or moisture as in unconditioned attics.  Remember, when planning for a conditioned attic space, ventilation is just as necessary as the rest of the home!  
4. Heating/cooling: In the US, the bulk of heating and cooling new construction is done by forced air systems.  That does not mean it is the best system, however.  Forced air creates pockets of warmth and cool.  Moving forced air through unconditioned spaces like attics and voids also allows for leakages.  In contrast, radiant heating creates an even, comfortable environment.   Here is a diagram that shows the difference:

According to BobVila.com, the benefits of radiant heating over forced air heating are several:

• Radiant heating consists of 50% infrared light, which is an invisible natural light that warms by proximity (ie, in the floors you walk on). 
• Air is not stratified like in forced heat systems.
• Radiant heating eliminates allergy symptoms that are generated when blowing air through the home.
• Distribution losses are nearly eliminated. 
• New products like WarmBoard heat and cool quickly and transfer heat better than traditional techniques of installing radiant heating. 
• Radiant systems can also be used to cool your home.
• Some studies show that radiant heating is up to 30% more efficient than forced air.
• Radiant heating will still need a fresh air system to exchange stale air with fresh, conditioned air.

Now, of course you can heat or cool water for radiant heating using any type of heater/cooler.  Geothermal energy uses the coolness of the earth about 18-30 feet below the surface, and only requires an electrical pump to circulate the liquid.  However, the installation costs for such a system makes payoff distant for most homes. Geothermal and radiant heating and cooling for large buildings such at the University of Southern California has been a cost-saving, long-term investment. 

The next best alternative to a radiant and geothermal systems is heat pumps (with high velocity mini duct system for distribution).  As with all forced air systems, if you take care of them, including changing filters regularly and caring for the air handler and condenser, they are great for heating, cooling and ventilation.

5. Ventilation: A good portion of our blog is devoted to ventilation, and we’ve come to the conclusion (as many building health experts have) that intentional, balanced ventilation in a highly sealed home is best.  It doesn’t matter whether you live in a pristine area with low humidity and pollution and prefer to open your windows most days; if pollen season or wildfire smoke or just cold winter air sets in, you will want to close your windows and still ventilate effectively!  For these reasons, it’s best to start with a tightly sealed home with dedicated, pressure-balanced ventilation installed.  Here are the features we would look for:

• Stale air is exhausted at the same rate fresh air is introduced into the home.  This will be 0.35 air changes per hour, but not less than 15 cfm (cubic feet per minute) fresh air per person (EPA.gov).
• Fresh air brought into the house should be filtered and conditioned (humidity removed or added and temperature adjusted) so that it’s not overloading the HVAC system and can be distributed to the home using only the air handler fan without need for the heater or compressor to run. 
• To be effective, fresh air can be continuous or run on a timed schedule every hour; it shouldn’t rely on a manual switch!
• Although there are situations that advocate for having separate ventilation and temperature control systems, in reality this creates redundant duct work.  An alternative is mixing conditioned outside air with the return air in the HVAC system in a mixing box.  
• An HRV (in non-humid climates) or ERV (in humid climates) optimize the exchange of energy between the intake and exhaust air. 
• In humid climates, a whole-house dehumidifier helps the HVAC system to keep the home at the right humidity without having to over-cool.
• Air quality monitoring for temperature, humidity and CO2 are the minimum variables but VOCs, CO and radon can also be added. 

6. Garage: Garages have become an extension of our homes because of their convenience for home access, ability to protect another very important investment (our cars), and for storage and hobby space.  However, not many people realize how garages impact the health of our homes.  You may know not to allow your car to idle while in the garage, but recent studies show that engines continue to emit benzene even after turning off the ignition.  Exposure to high levels of benzene over time can cause cancers like leukemia, and decrease red and white blood cell production.  “On average, benzene levels in houses with attached garages are three times higher than of other houses,” according to Deborah Schoen, the head of Health Canada’s indoor air section.  Therefore, we recommend that:

• homes with attached garages be sealed off from the garage with spray foam in the adjoining wall and ceiling
• Use ⅝” type X (fire-rated) gypsum board on the garage side of the walls and ceiling (if there is a room above), and use fire-rated caulk, adhesive, or expanding foam to seal up penetrations
• The door between the garage and house needs to be air-tight to avoid allowing hazardous gasses to leak into the home.  Install an insulated, metal, fire-rated door with a self-closing feature, so it won’t be left open accidentally.  A good weather seal is also imperative. (HGTV.com)
• Consider making the garage a negative pressure zone with an exhaust fan. 
• Always seal up paint cans, chemicals and fertilizer well
• Consider a detached garage or 3-sided carport

7. Wall and roof construction materials:  In the US, homes have been built with wood framing since our colonial days because it was cheap and plentiful.  Since then, we have been criticized for building with wood because of its weaknesses: fragility in storms and wildfires, its non-insulating properties, and susceptibility to rot and insects and mold.  Now, with lumber shortages due to the COVID-19 pandemic, wood prices are high and other products are getting due attention.  There are many traditional products that have mold-resistant chemicals added, but in general these chemicals may be as dangerous to those who are chemically-sensitive.  

According to Joe Lstibureck, an expert in home construction and insulation, the best place to locate the water, air, vapor, and thermal barriers is on the outside of the structure.  A “clever wall” combines all four of these layers in one layer.  Here is one way to do it:

If you need some points on building the perfect wall, roof and slab, check out this video and article!  Although it was written/filmed in 2010, it still holds true.  Building a healthy home requires that these layers are installed in the right order and connected to their counterpart on the wall, roof and slab.  

The following are some newer materials and methods for better insulation, weather and pest resistance than traditional wood framing.  Notice that any weather-tight cladding can be installed over them, although SCIP homes are typically finished in the concrete integral to the exterior of the panel.

• SCIP (structural concrete insulated panels) is a building system that resists earthquake, tornado and fire damage better than traditional wood framing.  It was innovated over 45 years in Austria by the EVG Company.  The walls are made with a structurally welded steel frame, which holds a layer of foam insulation.  The wall is then sprayed with 1.5” of concrete on both sides.  This “monolithic” construction is very energy efficient and long-lasting. New homes are constructed with custom-made panels, which reduce labor costs as well.  Here is a page showing SCIP construction.  RSG-3D panels are a form of SCIP construction.
• ICF blocks (insulated concrete form) have the insulation on both sides, and concrete is poured in the middle. With 2 layers of insulation, it can be between 4.8-12.7% more energy efficient than traditionally built homes, according to one study.  ICF blocks are made by different manufacturers, Nurdura being a notable one.  Nurdura offers several types of ICF which are manufactured to accommodate interior and exterior finishes, radiant heating/cooling, and a variety of wall designs.  The outer polystyrene acts as a vapor barrier, while the inner concrete acts as an air barrier.  
• SIP (structural insulated panels) are also pre-made panels, which have a sandwich of metal, OSB, magnesium-oxide, or plywood, with polystyrene in the middle.  They are made to support floor and roof loads. The SIPs are held in place with steel channels at the floor, sides and top, with screws that are common to metal construction. 
• Steel framing with cold-formed steel (CFS) is now cost-competitive since wood prices are higher.  Exterior insulation such as foam board can address the problem of thermal bridging, which is the conduction of heat through the steel frame.  This exterior insulation can provide all 4 barriers in one layer.

8. Flooring options:  Flooring can be a major source of VOCs and allergens, thus it’s important to make a healthy choice here. Hard flooring is preferable to carpet because carpet can harbor many allergens, but a HEPA vacuum can go a long way to keeping carpet clean.  Here are some materials in order of least VOCs, least allergenic and easy to clean, to more problematic. It is also important to check the underlayment and glues recommended to install your choice of flooring. (source: mychemicalfreehouse.net)

• Natural hardwood flooring with zero-VOC finish like tung oil
• Polished concrete
• Tile: marble tile, slate and concrete tile are all very safe options.  Ceramic and porcelain tiles should be tested for lead if the manufacturer does not give any warranties about it.
• Engineered wood with plywood base and zero-VOC finish
• Natural carpets: the best are made of wool or seagrass
• Synthetic carpets: PET polyester is very low in odor and off-gassing.
• Laminate flooring is generally low-VOC now, but look for GreenGuard Gold certification.  
• Cork flooring does contain binders but some are certified GreenGuard Gold.
• Bamboo flooring can warp, crack or split and contains quite a lot of resins or glues to hold it together.
• Vinyl planks and luxury vinyl planks are low-VOC, but do have “plasticizers” that have replaced phthalates.  

9. LOCATION: When moving into a new area, just like finding out how long it will take to get to and from work, it’s important to take time to study about geography, topography, windflows and potential pollution areas to know how they will affect your home.  We’ve written on how green space around your home can positively affect your heart health–so it’s best to buy in the greenest neighboorhood you can afford!  Conversely, less green places like cities with few parks and trees negatively affect heart health, because trees absorb pollution like ozone and fine particles, and reduce stress.  Then, there are the geological characteristics of the locale to take into consideration.   For instance, although California on the whole is a highly desirable state to live in, some pockets of California have terrible air quality because of geography.  In the San Joaquin valley, smoke from surrounding wildfires can get trapped for extended times, agricultural burning was practiced, and increasingly hot days cause ozone problems (pbs.org). This area feeds many with its rich farms and soil, but the migrant workers who harvest crops are most subject to the dangerous air quality.   Likewise, homes in the prevailing wind path of airports experience levels of ultra-fine particles (UFPs) that are several times higher than homes outside these areas.  Here are some other critical locations and situations to be aware of:

• a busy thoroughfare or bus station
• oil wells or refineries
• trash dump
• Chicken or cow farm
• Stagnant farm pond or standing water (like used tire recycling center)
• neighbors who burn trash or wood consistently
• farms that crop dust or use aerosolized fertilizers
• Areas that employ insecticide spray trucks
• Golf courses and other public areas that use copious lawn treatments
• Businesses that perform outdoor renovation work like sanding or spray painting
• Seasonal issues like wildfires, tree pollen, ragweed, etc.
• Neighbors who cook odorous foods, smoke, barbeque meat, have bonfires, etc. 

10. General air flow/floor plan: Traditional home design features defined rooms for living, dining and kitchen space.  In contrast, open floor plans have become quite popular in recent decades.  Open floor plans can create better cross-ventilation and air circulation, but we understand that life after the COVID-19 pandemic may require more walls, doors and private space in order to accommodate the many functions of working, learning and staying at home. (prnewswire.com)  Make sure that whether it’s time to throw open the windows or keep them shut, your floor plan works with natural or mechanical ventilation, instead of against it. Here are some aspects to consider:

• The number of house stories depend on style and space available to build. With multiple stories, ventilation becomes more complicated.  The “stack effect” of hot rising air is more pronounced with taller home height, and if air circulation from the bottom to top is unimpeded, this channel can provide significant cooling through ventilation.  The architect of an antebellum residence Longwood in Natchez, Mississippi, planned on this effect during design of the octagonal house that contains a basement and 7 stories above ground.  A center gallery was incorporated into each floor with doors to rooms and verandas on opposites side of the building, so that air flow was unimpeded through the outside doors and windows to the center galleries and up through the cupola of the home.  A modern home could incorporate a central courtyard for the same effects: natural light, cross ventilation, separation of spaces, and the psychological and physical benefits of plants and the outdoors. (fraherandfindlay.com)
• Layout of the home should not only consider views to the outside, but prevailing winds and penetrations such as doors and windows.  
• Types of windows are very important to ventilation. Casement windows are one of the top choices, as they can be opened fully for maximum ventilation.  Next, awning windows hinge at the top and provide the option of opening windows even when it’s raining.  If you live in a pollution-prone area, you may opt for double-hung windows, which can be opened vertically to allow the use of pollution-controlling window screens at the bottom.  Plus, you can allow cool air to enter through the bottom and warm air to exit through the top.  If your ceilings are tall, this effect is even more pronounced.  
• Ceiling height: if you have a large open space with high ceilings, it is either prime for a big fan to circulate cool air (see our post “What’s the deal with those big ceiling fans?” or skylights or high windows to exhaust hot air. 
• Location of the kitchen: The kitchen is still a source of heat and odors, so the placement of the kitchen and its exhaust vent hoods can assist in house ventilation.  Balanced exhaust hoods are a new design that pull air from the outside as well as exhausting heat and vapors, so that a strong negative pressure is not created in the home. 
• Hallways: Going back to past centuries, hallways were important to provide a private buffer for bedrooms, access to common washrooms, and ventilation.  The “dogtrot house” had a central hallway that separated rooms on either side, providing a breezeway and common area in the center.  Narrow hallways might be considered a waste of space, but with enough room, they can contain useful features like a sink to wash hands, concealed laundry, creative space, art display, etc.  (matthewjamestaylor.com)  
• The use of partial walls and glass can “define” space without limiting ventilation.  Where walls and doors are needed, such as bedrooms, consider the old-style use of transoms over doors, or in-door ventilation grilles. 
• Room use increases air circulation, because body movement and heat naturally causes the air within the room to move too.  Traditional homes may include a dining room that rarely gets used when the family eats in the kitchen, but by making such a room multi-purpose, the family gains access to more livable space. For example, you can create a bookshelf wall on one end with comfortable chairs, a large table that can serve as dining, craft or homework space, and mobile carts that can wheel away supplies or serve food when needed. 
• Furnishings: overcrowding a room with large furniture or using a room for dedicated storage creates air flow problems that can lead to mildew and poor air quality.  If possible, maintain spaces between furniture, and never cover an air vent with furniture (you can purchase “vent extenders” though). 

Well, those are some of our best suggestions for living comfortably and health-fully…only the sky (and budget) are your limits! 

Grilles, registers and diffusers: what they are and how to prevent condensation on them

I ran across the term “diffuser” while researching another topic and they were new to me in terms of ventilation.  When and where should they be used?  What is the benefit of a diffuser?  To start, let’s take a look at three similar products that have some overlapping characteristics and uses: grilles, registers and diffusers.   (source: jonite.com)

Grilles can be used on the intake (return) to HVAC systems, as well as the distribution.  They have fixed bars or louvers that don’t direct air as much as keep large objects from entering the ductwork.  They have no moving or adjustable parts.  A grille can also be placed in a door or wall to allow air movement between the two spaces. 

Registers are most likely what we grew up with in our homes: they are grilles with adjustable dampers.  The dampers can change airflow direction somewhat, or shut it off completely.  The typical rectangular register with flow damper is very common as a supply vent cover but is never used as a return (intake vent).

HVAC design can be somewhat complex, although many residential installers have simplified the systems to fit more homes with standard products.  If you really want the best performance out of your AC system, it’s time to look at diffusers.

When you need to distribute air evenly around a room, diffusers are the right choice, as the louvers and dampers are multi-directional.   Diffusers come in a multitude of shapes and designs to accommodate and hide ventilation outlets.  For example, InViAir has many different styles and sizes to accommodate design taste, lower noise (no one likes to hear the rush of air coming out of registers in a quiet room), and minimize condensation.  Diffusers can also be combined with lights so that they accomplish two functions in one unit, decluttering a space visually.

One problem home and business owners can encounter is water dripping from a vent and discoloring the surfaces below, and the ceiling itself.  There are many reasons a vent terminal can drip water, and it happens most often in the summer season.  Condensation is not just a problem of water dripping onto the floor or other surfaces; if the condensation continues, it can be a prime habitat for mold.  The condensation usually occurs because of one of two conditions: either the air in the room is too humid, or the supply vent is too cold. (energyvanguard.com) 

Here’s how to find out what is happening: check the room humidity with a humidity sensor like these that shows Temperature and Relative Humidity.  Then, go to a dew point calculator and input the room temp and relative humidity to get the dew point.  This is the dew point of the room after air has mixed in it.  Now, bring the sensor to the vent itself (carefully use a ladder if necessary.  Read the temperature of the air coming out of the vent.  If the temperature of the air coming out of the vent is at or below the dewpoint, the condensation is occurring because the cold air is hitting the warm, moist air of the room and water vapor from the room is condensing on the cold metal.  

There are two main solutions to prevent the condensation: reduce the relative humidity (RH) of the room (house) so that the dewpoint associated with the temp and RH is below the incoming air temperature, or increase the incoming air temperature.   Check out our post on a healthy home inventory regarding sealing the indirect leaks, direct leaks, attics, fireplaces and crawl spaces, before you go looking for smaller leaks such as doors and windows. 

How can you increase air temperature coming into the room?  According to energyvanguard.com, the two main causes of excessively cold vents are low refrigerant level and low air flow through the system.  An HVAC tech will need to check the refrigerant level, but here are the low air flow problems you can check:

• a dirty filter

• a filter that is too restrictive (higher MERV) than the system was designed for

• Blocking of return or supply vents by furniture, rugs, or other items

You can also ask the HVAC company to check that the cooling coil is not dirty, or that the ducts themselves are the proper size (I found out that the return air ducts in my home were too small for the system).  Here are some other remedies you can do yourself if you are not allergic to dust or fiberglass:

• If the duct above the vent has insufficient insulation or gaps in the insulation, then water vapor from the hot, humid attic air can condense on the duct and drip down into the room or on the ceiling around the vent.  You’ll need to go into the attic and bring some insulation, foil tape and knife or scissors with you.  Replace and seal all insulation gaps on the ductwork, all the way down to the ceiling (make sure the boot is properly sealed to the duct first; see the next point). 

• There are two components to the vent terminal: the boot (the part above the ceiling that connects to the duct) and the vent terminal, which is the grille, register or diffuser below the ceiling.  If these are not properly connected/insulated, then you can have condensation.  

• If the leak is between the boot and the duct, it should be sealed with a mastic sealer. If it’s between the register and the drywall, you can seal the leak using caulk. If you can’t find the leak, call a professional air conditioning company for help. (source: cooltoday.com)

• Condensation can occur on vent terminals when cold air coming out of the duct chills the metal of the terminal, and water vapor from the warm, humid air in the space condenses on the cold metal.  You can exchange a metal grille, register or diffuser with a plastic or composite one.  These diffusers by InViAir are made with a proprietary composite material that prevent condensation. 

It may take some time to prevent those pesky drips, but it’s worth it to avoid the mold!

How’s the air quality in your laundry room?

To be honest I hadn’t thought about this one before…it usually smells nice inside when I’m doing laundry (because of scented laundry products), and it smells nice outside too, because of the scent coming through the dryer vent!  Our brains are trained to equate nice smells with fresh air,  but read on to find out exactly how good this air really is.

For some years now, we’ve known about microfibers from clothing that get washed out into waste systems, streams and rivers, eventually ending up in the ocean, marine life and even tap and bottled water.  But recent research shows that an even higher quantity of microfibers are being released to the air through dryer vents over those that are washed down the drain.  These microfibers are in the fine to ultra-fine particle range, and contribute to overall outdoor air pollution.  This, in combination with the VOCs emitted with the laundry products* is not good.   Although the researchers found that smaller pore size on the dryer lint filter as well as use of a single to double-dose of laundry softener reduced the outdoor emissions, a lot of microfibers are still being released into the air.  All of my training at HypoAir led me to think, if that much is going outside, how many particles are going into the air inside?  Fine and ultra-fine particles are a hazard to our respiratory system and whole bodies (see our post “What are ultrafine particles and where do they come from?”).

Since we at HypoAir are not going to advocate for using commercial laundry softeners (one softener used in the study was Bounce, which receives grades of “C” - “F” at EWG.org), here are some of the other ways you can reduce fine particle pollution in your home and outdoors:

• Use non-toxic detergent strips and laundry pods to reduce VOCs.
• Use spot cleaning and other methods to keep your clothes fresh,  to reduce washing.  
• Dry clothing outside when and where possible to avoid release of microfibers
• For washing: GuppyFriend and Cora Ball catch microfibers before they are washed down the drain (GuppyFriend also prevents fibers from breaking off your clothing). Or, install a microfiber filter from Girlfriend Collective on the drain 

Microfibers are just one part of the air quality problem emanating from laundry rooms.  Other parts include the carbon monoxide (CO) emitted from gas dryers as a byproduct of combustion, and water vapor from all dryers as the clothes dry out.  Dryer vents are meant to exhaust all of these safely outside–if they are sealed tightly.  Here is the proper way to seal a dryer vent from the machine to the wall:

• Don’t use duct tape!  Despite its name, the adhesive on duct tape is not suited for dryer vent use.  It can dry and crack over time, causing leakages. (source: bestairducts.com)
• Do not use screws to connect sections of ductwork together because the sharp end can catch lint inside the duct. (dryerventwizard.com)
• Use foil tape to seal each joint of the ductwork. Here is a video showing how to apply foil tape.
• To install a dryer in a new place, here is a more in-depth instructional on how to run the dryer vent line. 
• Make sure the vent is properly sealed to the exterior wall.  Here is how to reseal a vent to the wall.  
• Do not terminate the duct in an attic or crawlspace!  It must go directly outside.  

If you run the dryer with a load of laundry and you feel that the humidity is appreciably increasing in the room, it’s best to investigate for leaks in the dryer vent line as soon as possible, because that means that microfibers, water vapor, and possibly VOCs and CO are coming into your living space.  The dryer vent is meant to be a low-pressure line for exhausting these products.  Another cause of malfunction is letting dryer lint build up in the line, which causes higher pressure (if this happens you may also notice your clothes are not drying as quickly).  The dryer line should be cleaned once a year, so that lint does not build up and cause a venting problem or fire hazard.

Finally, here are a few “upgrades” that can make your laundry room an area of good air quality instead of a hazard:

• Since the washing machine, wet laundry and dryer heat all combine to add more humidity and heat in this room, consider installing a separate exhaust fan in your laundry room to run while doing laundry.  
• Plug in a Mold Guard/Germ Defender in your laundry room to mitigate mold from increased humidity, PM2.5 from microfibers/lint, and VOCs from laundry products.

With some inspection, planning and improvements, your laundry room can be a more healthy place!

Can I avoid mold with JUST ventilation?

Here’s the spoiler: many times you can, sometimes you can’t, but read on to find out more!

This post was borne after reading a very interesting article in The Atlantic.  The author lives in an area of coastal Japan, which is dry and beautiful for ten months out of the year and very humid for the two months of summer.  During the two humid months, he struggled with mold growth in his home and tested dehumidifiers, air conditioners, and finally fans and open windows.  When he used the fans to find the perfect amount of ventilation, the surfaces stopped forming fuzz overnight and his shoes stopped smelling like loaves of bread.  He also pointed out that according to research, he was much less likely to get sick from coronavirus or any other airborne disease with fresh air constantly diluting the rooms.  I wanted to know, is good ventilation the number one key to avoiding mold problems?  Is it possible to live healthy with only fresh air ventilation?

First of all, we are very accustomed to living in air conditioning.  It may not always be needed, but it’s everywhere: the office, the grocery store, the gym, school, and of course, our homes.  Except in select areas of the US, homes without air conditioning are even viewed as less valuable.  

Is your climate temperature livable without air conditioning?  Considering that the US was settled before the advent of air conditioning, then the answer is mostly yes.  Of course, there are the desert areas like Las Vegas where extreme temperatures would make it very difficult, if not impossible, to live year round.  The cement and asphalt of the city make it hotter today than it was during its historical roots, but on the day of the famous land auction which settled Las Vegas, men were standing outside in 110 degrees in wool suits, which means nowadays we have adapted ourselves out of the outdoors and into air conditioning. 

Then, we have humidity.  High humidity combined with high temperatures, as we describe in this post, impedes evaporative cooling of our bodies, to a point that 95 degree wet-bulb temperature is the maximum limit of temperature and humidity.  If the climate increases beyond this (as it has for periods in India and other areas), mechanical cooling like air conditioning is necessary.  

Then, we have pollution.  Outdoor pollution from vehicles, airplanes, industry and a slew of other sources sometimes necessitates closing off our homes and filtering air coming in for breathability.  

These are some of our human limits of comfort and endurance.  But if air temperature, humidity and outdoor air quality would allow us to live without air conditioning, do our homes need it to avoid mold and be healthy?  If not, what is the upper limit of humidity, such that good ventilation can keep mold in check?

There are different climates in every state in the US, and many of them are perfect for living without air conditioning.  Southern California and Hawaii come to mind, for example, but according to AprilAire, Hawaii is in the top 10 most humid states!   Here they are in order of decreasing humidity:

1. Alaska

2. Florida

3. Louisiana

4. Mississippi

5. Hawaii

6. Iowa

7. Michigan

8. Indiana

9. Vermont

10. Maine

Looking at this list, 4 out of 10 (Alaska, Michigan, Vermont and Maine) are among the most northern states, yet they are also among the most humid!  Temperature-wise, homes in these states don’t need air conditioning for many days during the year, if any.  Yet we know that humidity is a big factor in maintaining healthy air, so how is it possible to keep a healthy home in a humid environment without air conditioning?  

Ventilation is the primary key.  According to the Air Infiltration and Ventilation Centre (AIVC, an international organization), ventilation is “the process by which ‘clean’ air (normally outdoor air) is intentionally provided to a space and stale air is removed. This may be accomplished by either natural or mechanical means.”  For our purposes, we will discuss the distribution and quantity of that fresh air.  If the ventilation system delivers the right amount of fresh air, but does not circulate it throughout the home efficiently, then most of the home can be stale and ripe for mold growth.  If the distribution is right but not enough fresh air is introduced, indoor contaminants are not diluted.  To put it succinctly, in many homes, distribution AND quantity of fresh air are lacking.  Let’s look at them individually.

Distribution

We’ll look at distribution first, because it often determines how the fresh air comes in.   If you live in a naturally pristine area like the coast or country where you can leave your windows open or cracked for most seasons, this is an ideal way to bring in fresh air.  In this case, check into installing a whole-house fan, which will pull air from every cracked window and exhaust it through a vent in the roof or attic.   This page describes the use of a whole-house fan, including the recommended air flow for specific climates like coastal, desert, mountain or inland.  Such a fan is recommended because it takes the guesswork and legwork out of setting up ventilation scenarios for each room of your home.  In order to be able to leave windows open for extended periods even during rain or allergy season, check out these adjustable screens, which filter out most pollen, 95% of rain and 69% of UV rays.  

If installing a whole-house fan is not possible, then you’ll need to experiment with portable and ceiling fans in order to get that fresh-air moving throughout each room.  Open windows and doors across the house to get cross-ventilation, and try to direct the flow from the cooler to the warmer sides of the house to exhaust hot air.  Although it may take more work to set up, a manual ventilation system can be just as effective as a whole-house fan if used continuously.

• Ceiling fans are a low-cost way to keep air from becoming stagnant in any room. 
• Portable fans can be set up in windows: 
  • Box fans are low-cost but they will need to be moved and windows closed every time rain may threaten. 
  • New window fans are smarter:
    • The EcoBreeze 2, $229, has a built-in filter, temperature sensor and humidity limit so it will bring in fresh air whenever the temperature and humidity outdoors allow.
    • Bionaire Window Fan with Twin 8.5” Reversible Airflow Blades, $70, has a water-resistant motor so that light rain won’t bother it.
    • Lasko 16” Reversible Window Fan with Storm Guard, $120, allows you to close the window without moving the fan for those really big storms.

At HypoAir we always recommend maintaining a humidity of 40-60% in your home in order to keep mold and germs at a low level.  I went back to a study performed before the widespread use of air conditioning in homes, in order to find out how they prevented mold in the “olden days”!  An extensive experiment conducted over one year and published in 1953 showed that the amount of mold that grows on a substance depends on the nature of the substrate (material) and the relative humidity (RH) in the air above it.  Leather, cheese, wool cloth, wood, cotton cloth, and glass wool (like fiberglass) were tested in sealed environments of different equilibrium humidities.  It was found that:

• “In humidity tests of one year's duration, leather and cheese were susceptible to growth of mildew at 76 per cent R.H. and higher; wood and wool mildewed at 85 per cent R.H. and greater, while cotton cloth and glass wool failed to mildew at 92 per cent R.H. but mildewed at 96 per cent and 100 per cent R.H.” 
• An atmosphere of 65% RH or less “might be considered safe for permanent storage of all materials (studied)”.
• “...molds obtain their moisture directly from the substrate rather than from the moisture in the air…The minimum humidity for the occurrence of mold growth was related to the equilibrium moisture content of each material at each humidity…”
• “It is concluded that the water-absorbing properties of the substrate play an all-important role in determining the limiting humidity of the atmosphere at which mildew will occur. It is postulated that the fungus is incapable of obtaining moisture for mycelial development directly from the atmosphere (except at 100 per cent R.H.) but derives it from the substrate which obtains the moisture from the atmosphere.”

In layman’s terms, each substance (leather, cheese, cotton cloth, etc.) had a different minimal humidity at which mold grew.  The substance absorbed water from the air, and the mold spores took their nourishment from the water in the substance and the food in the substance. If the humidity in the air was kept low enough so that the substance could not absorb the minimal amount of moisture for mold growth, no mold would form on it.  This experiment did not employ any ventilation, so we will go into that next.

How did our ancestors keep the humidity in their furnishings and clothing down when the air coming in from the outside was humid?  Ventilation is still the answer.  Ventilation helps evaporation, which lowers the moisture content of the substance, and here is how.

Evaporation is the movement of water from its liquid form (in the substance) to its vapor or gaseous form, that we call water vapor (serc.carleton.edu).  Evaporation is influenced by temperature, relative humidity and wind.  Higher temperature = more evaporation. (Evaporation rates are higher at higher temperatures because as temperature increases, the amount of energy necessary for evaporation decreases, and higher temperature air can hold more water vapor.) Next, higher relative humidity = less evaporation. (The more humid the air, the closer the air is to saturation, and less evaporation can occur.)  Finally, more wind = more evaporation. (Wind moving over a water or land surface can also carry away water vapor, essentially drying the air, which leads to increased evaporation rates.)  Therefore in a house, hot dry air circulating is great for preventing mold, but generally on a summer day we can get 2 out of 3: heat, higher humidity, and circulation.  

Here is a more detailed explanation of how air circulation helps evaporation: “Evaporation increases the humidity of the atmosphere that immediately surrounds the liquid. This humid air takes some time to dissipate into the rest of the atmosphere. The presence of a breeze, a powerful wind, or some other form of air circulation can speed up this process and make the environment of the liquid less humid. Therefore, by decreasing the humidity of the liquid’s surrounding, a powerful breeze or wind can increase the rate at which the liquid evaporates.”(bjyus.com)

This leads to the conclusion that the RH of the air can differ from RH of the substrate.  Scientists have devised a different term for RH of the substrate, calling it water activity, aw, which is expressed as a decimal, or equivalent relative humidity “ERH”, which is expressed as a percentage.  (We’ll stick with ERH in order to compare it directly with RH of the air.)  ERH is equal to RH at the surface of the material only when the system is confined to the extent that the atmosphere above a moist surface is at the same vapor pressure and temperature as that directly at the moist surface. This is called a “steady-state”.  In actual environments, however, there is usually a gradient of vapor pressure from the surface into the air above or vice versa. Since RH =partial pressure/vapor pressure x100%, and vapor pressure in the atmosphere is variable, this means that RH is constantly varying throughout a room.   This means that ventilation, which affects vapor pressure at the surface of the substrate, affects relative humidity of the air contacting the substrate to determine the ERH (the moisture content of the material). 

In a more recent (2019) study on ventilated insulation panels for housing, ventilation channels are shown to intensify removal of moisture from insulation, meaning that ventilation dried the insulation: “...even with a high humidity of the indoor air of about 70%, the relative humidity of the air in the material of insulation did not exceed 50%, which provided high heat-protected properties of the panels.”

A second recent (2020) study of homes in the UK found that higher concentrations of mold, and thus more “moldy odors” are found in bedrooms rather than living rooms.  There are several reasons for this, even though the average humidity in both rooms was very similar.  The presence of more people in living rooms naturally causes more circulation of air in living rooms.  Also, the presence of large pieces of furniture such as wardrobes and beds placed near walls in the bedroom impedes circulation of air.  Thus, circulation of air was implied to lower the mold concentration in the living room over the bedroom.

According to Cleaning and Maintenance Management, a property restoration company, here is how we can understand the drying process: “Low relative humidity (RH) is necessary for drying, as moisture in materials and air seek equilibrium. The lower the RH of the air, the quicker the wet materials will give up their moisture to become equal with the moisture in the air. …Air movement is the workhorse of drying by displacing high RH at the surface of wet materials with lower RH. Circulation airflow moves wet air to our dehumidification systems (either mechanical or ventilation), allowing us to manage RH and water vapor in the air. 

Next, we’ll explore how the quantity of fresh air to bring in is determined by the advised minimum, and by temperature.

According to the EPA, ASHRAE  (formerly called the American Society of Heating, Refrigerating and Air-Conditioning Engineers) recommends (in its Standard 62.2-2016, "Ventilation and Acceptable Indoor Air Quality in Residential Buildings") that homes receive 0.35 air changes per hour  but not less than 15 cubic feet of air per minute (cfm) per person. 

Too much fresh air can be bad in hot, humid climate, because heat increases the amount of moisture air can hold.  A 2013 study showed that in very humid climates (like Bangkok, Thailand), reducing ventilation to the minimum (by ASHRAE) reduces indoor mold formation.  This is due to the fact that bringing in air from outdoors that is greater than 70% humidity, increases humidity inside.  This is not the case in a lower humidity climate like State College, PA, where they conducted a similar experiment: indoor humidity did not increase above 70% because outdoor humidity was not high. 

Too much fresh air can also be bad in cold climates, because bringing in cold air can cause condensation.  A study in Sweden showed that in cold attics where insufficient sealing caused warm air to leak through the upper ceiling into the attic, traditionally vented attics allowed too much fresh cold air into the attic and caused condensation on the underside of the roof, resulting in mold and rot.  “The optimal air exchange rate varies with the outdoor climate, and fixed ventilation through open eaves and/or gable and ridge vents is not always the best choice. To get optimized ventilation regardless of type of external climate, attic insulation, airtightness, etc., ventilation must be controlled and adapted to the present situation. By using sensor technology and mechanical ventilation and making the attic as airtight as possible, this can be achieved.... A basic system would comprise mechanical fans and dampers controlled by attic and outdoor climate sensors installed in a sealed attic without vents. The ventilation system runs only when the outdoor air has a potential to dry out the attic.”

In the article “Ventilation won’t prevent attic mold growth” by Jeffrey May, Founder and Principal Scientist of May Indoor Air Investigations LLC in Tyngsborough, MA, various attic situations with ventilation showed mold due to warmer air leaking into the cold attic space from the home below, causing condensation.  These were usually mediated by sealing the attic floor better (for example, sealing the attic stair access and older can lights) or converting the attic to a conditioned space by sealing it off from the outdoors and providing more insulation. 

In the basement, EZBreathe is a product that operates on sensors to draw humid air out of the basement, ventilating with less humid air from the upper levels of the home.  Although we generally advocate for a balanced ventilation system instead of the slight negative pressure generated by EZBreathe, it does work to keep the basement area at a lower RH than it would have by just opening windows. 

A 1993 study showed that in an apartment in Japan, fungal indices were the highest in the corner where the northern and eastern walls faced outdoors.  This is because these walls were colder (they faced away from the sun), causing higher relative humidity inside the room.  This cautions us to pay special attention to rooms on the north side of your house.

In these five insulation, attic, basement and home situations, sensors in each space can be useful to know how much outside air to bring in according to the conditions in that space, in order to avoid mold.  According to the EPA,  “Mold and mildew growth can be reduced where relative humidities near surfaces can be maintained below the dew point.

The best way to explain this (per this great article) is to find out the dewpoints of the indoor and outdoor conditions.  If the outdoor dewpoint is lower, you can ventilate with fresh air and still dry out your house!  For example on July 26, 2002, here are the conditions inside and outside my house (a relatively “dry” hot day outside!):

Inside: 76 deg F, 67% humidity = 63 deg F dewpoint (dpcalc.org)

Outside: 91 deg F, 54% humidity = 72 deg F dewpoint (dpcalc.org)

See, even though the relative humidity outdoors is lower, if I open my windows, that hot air coming inside would be cooled and relative humidity would increase, working against my humidity goals.

Mold is not the only byproduct of high humidity in our homes.  Dust mite fragments and excrement are a main allergenic component of household dust, and dust mite populations increase when more humidity is present (1996 study). “Laboratory studies of D. pteronyssinus suggest that optimal conditions for growth and development occur between 70% and 80% RH at 25°C, with acceptable ranges of 55% to 80% RH and 17°C to 32°C (Anderson and Korsgaard 1986).”  Mites ingest water directly from water vapor in the air through special glands. 

In addition to distribution and quantity of fresh air, a minute amount of temperature control in colder climates makes a big difference.  Mechanical ventilation can actually keep indoor humidity lower than the outside air it brings in if the temperature is raised slightly.  Cold foggy air has a high RH.  However, if you warm up that same air, the relative humidity drops because warm air has a higher capacity to take moisture.  Even on a cold, foggy day, you can fill up the house with 100% humid air, warm it up and have much less than 100% humidity inside the house. 

Finally, we have a device that our ancestors did not have in fighting mold and mildew: bipolar ionization.  From personal experience, adding a Mold Guard/Germ Defender unit to a small humid space like a bathroom or laundry room essentially eliminates mold formation, even if the ventilation does not keep the moisture content of the towels, wood and surfaces below what inhibits mold formation.  The positive and negative ions constantly destroy mold spores and inhibit mold formation.  An Air Angel can provide the same protection on a slightly larger scale (up to 300 ft2).  On the largest scale, a Whole Home Polar Ionizer installed in the HVAC system distributes these ions to every room and destroys mold spores throughout the house.   

So, the interesting takeaways from these studies on ventilation let us know that in many cases we can control mold without air conditioning, as long as we pay attention to:

• ventilation distribution, which is the distribution of incoming air to every space and velocity of air within the space.
• Ventilation fresh air quantity, which is the amount of outside air to bring in
• Temperature, which can affect evaporation and condensation
• Use of a BiPolar Ionization device.

Knowledge about how mold forms is a blessing that we can use to deter it!

Power Outages and Air Quality

It’s not hard to imagine nowadays: hot weather, cold weather, storms, electrical grid system hacking, or just plain equipment failure are all reasons you could lose power to your house.  In that case, there are a number of things to consider and ways you can prepare. 

Generators:  If you are going to keep a generator as a backup power source, have a plan on where you will run it.  It’s NOT OK to run a gas-powered generator in an attached garage, or even next to an attached garage.   According to the U.S. Centers for Disease Control and Prevention, CO poisoning sends more than 20,000 Americans to the emergency room and kills upwards of 400 during a typical year. (USNews.com) Gas-powered generators need to be placed at least 20 feet from the house, so that exhaust fumes can dissipate. To plan for this, make sure you can roll the generator to a safe operating place (preferably a fenced yard) and have a dedicated extension cord of the proper gauge wire to run to your home.  Inside your home, you should have a working CO monitor on each floor so that you can be alerted should the CO level rise. Change the batteries in the CO monitors once a year when you change smoke alarm batteries.  CO doesn’t even need open doors or windows to enter your home, so don’t circumvent these guidelines!  Other safety tips for generator operation: (redcross.org)

• Keep fuel in approved safety cans
• Be sure to shut off the generator and let it cool down before refueling
• Don’t operate it in wet conditions; you can install a tarp or other temporary cover over it to keep it and the ground it’s standing on, dry.

Window screens:  Of course, ventilation sans electricity requires planning too.  It’s hard to keep the windows open for ventilation without proper-fitting screens.  If you don’t normally open the windows, now is the time to plan for having to do so. 

1. Get windows working (here’s a video on how to unstick painted windows using a variety of tools and techniques). 
2. If your windows are missing screens, plan to order at least one screen per side of the house, per floor.   You’ll want to allow cross-ventilation, so this means if you have a traditional four-sided, two-story house, you’ll need at least eight screens if you keep the interior doors open for cross-ventilation.  For bedrooms with multiple windows, it’s helpful to have an additional screen (2 total) in the bedroom so that you can get cross ventilation in the bedroom, even with the door closed.  Here’s a page that will help you order the right size screens and the right hardware.  Or, order adjustable window screens that will fit many different size windows.   
3. For existing screens, consider having them re-screened in new material like AllergyGuard or PollenTec.  These screen materials are actually fine filters that block way more pollen, dust, and particles than traditional screens.  AllergyGuard boasts that it blocks particles from 0.3 to 10 microns, more than 69% of UV Light and 50% of Infrared Light, and over 95% of water and rain spray (allergyguard brochure). 

Cookstoves:  Electrical outages don’t necessarily mean eating cold canned food if you have a gas grill.  The grill could be standard or mini size ($89 at Amazon); the key is having the proper fuel ahead of time.  This mini grill is designed to run on small propane tanks (about 5 lb cylinders), but with a connective hose you can connect it to a larger cylinder.  As with any unvented gas appliance, it has to be placed outside!  Open carports with a cross-breeze are an ideal place to grill and stay protected from the weather.  Another option is to go old-school and have a small charcoal grill and bag of charcoal on hand.  Charcoal grilling takes a little practice; the key is building a hot bed of coals before starting to cook.  In order to eliminate the use of lighter fluid (the fumes of which go right into your food and cause photochemical smog), use a chimney starter like this one to get the coals nice and hot for a great grilled meal.  Alternatives to using a chimney starter are placing a charcoal briquet in each compartment of a cardboard egg carton, closing it and lighting each end of the carton, or placing wadded up newspaper below a pile of charcoal briquets, and lighting the newspaper.  These methods allow the cardboard or newspaper to burn slowly and allow time for the charcoal to catch fire.

Avoiding mold:  Without air conditioning and dehumidification, it's only a matter of time before mildew and mold will start to grow.  

• Ventilation is the first key to prevention in this case.  If possible, open windows on opposite sides of the home to get cross-ventilation going.  
• Use safe cleaning products that kill mold and odors: 
  • TotalClean uses iodine to safely kill mold and bacteria.  It even eliminates odors when sprayed in the air near trashcans and pet litter.
  • Concrobium Mold Control Spray uses a non-toxic trio of salts to kill mold and prevent future mold from growing.   You can spray it on draperies (test on a small area first), wood, and other furnishings to prevent mold when you’re not able to prevent high humidity. 

Staying cool:  Sleep is essential but it’s no fun trying to sleep when it’s hot.  Fans provide evaporative cooling (moving air that causes moisture to evaporate from your skin, taking heat with it).  Here are some innovative products to get cool and get some z’s:

• Portable battery fan: This model from Treva is lightweight and runs an amazing 65 hours (source: camping review) on one set of 6 D-cell batteries.   It also has an AC adapter for use when the power is on.
• Got an old-fashioned hot water bottle?  Fill it with one layer of ice cubes to chill down your bedding and keep you cool.  Or, strap small ice packs to your body’s pulse points (wrists, ankles, back of knees, armpits) using sports bandages or long socks.
• Sleep out in the open.  Before modern air conditioning existed, the concept of a “sleeping porch” was used in the summer.  If it’s very hot, you can try sleeping on a covered porch with some protection from bugs.  You’ll need: 
  • A portable bed, cot or hammock so the bed is elevated off the floor for more ventilation
  • A mosquito net to protect from biting bugs:  there are many to choose from!  Try a single net for one person, or an outdoor screen house for several people

It’s an unpredictable world, so a little preparation will help you not to “sweat” the inconvenience of losing power.  Let us know what innovations you come up with to stay safe and cool during summer outages. 

Air-Sealing your Home

Wow, the revelation that Ultrafine Particles (UFPs) from outdoor pollution can easily penetrate a home’s interior through cracks and leaks has really stirred our thinking.  Specifically, a 2018 study on UFPs from airport traffic during prevailing winds caused indoor pollutants to rise by 1.7 fold (170%), and HEPA filtration inside the homes only lowered them by 33%.  What does this mean?  Our homes are leaky, and no amount of indoor air filtration can keep up when outdoor pollutants are raging!  This could be wildfires, oil refineries, a major highway, a major port, or any heavy industry or power plant.  Basically, the only way to keep outdoor pollutants outside is to either seal the building envelope better, or use a positive pressure system where the inside of the building stays pressurized, so that airflow is always inside to outside.  

Before we get into the specifics, home builders in the past usually only concerned themselves with one barrier, a vapor barrier.  This was the felt paper, housewrap or other system installed under the cladding that prevented rain and moisture from entering the building.  A vapor barrier is not the same as an air barrier, and air barriers are much less common in residential and even commercial construction.  We’re talking about air barriers in this post, as air barriers are one way to block UFPs from entering your home.  

Here are some options for making an air barrier (sealing the building envelope):

From the outside: this is best accomplished during construction or major renovation:

• Applying a membrane air barrier like Delta Vent SA over sheathing involves primer, tape and the barrier; this video shows how it is installed and the tape is preferred to caulking in preventing air leaks.

• Spray Wrap MVP from Prosoco can be used as the primary air barrier over above-grade wall assemblies prepared with joint and seam filler.

From the inside: there are 3 ways to seal the inside: Before drywall, using the drywall itself as an air barrier, and after drywall. 

• Before drywall: 

• Use a product like Knauf Insulation EcoSeal, a waterbased elastomeric sealant.  First the exterior sheathing is installed and taped.  Then the sealant is applied to all interior seams and cracks with an airless sprayer at 1700 to 2200 psi, which really forces the sealant into any cracks. It fills gaps from 1/16” to ⅜”.  Here is a description of how it’s installed. 

• OwensCorning EnergyComplete is a two part insulation and air-sealing system.  First a latex sealant is sprayed on the interior of sheathing (like Knauf Insulation Ecoseal), then the wall cavities are filled with either blown-in insulation (by using netting to retain the insulation) or with spray foam. 

• You can apply an air barrier like Intello Plus (ceiling video, wall video, penetrations video) on the underside of ceiling joists, all along walls, sealing it to the subfloor.  Again, run a blower door test before installing drywall so that large leaks can be corrected. 

• Use spray foam: spray foam is seen as a one stop shop that insulates AND seals, but it requires careful installation and checking through a blower-door test.  This article shows how an older house that is renovated with sprayfoam insulation can be surprisingly leaky.  The application of the foam is incredibly important in creating the seal, as small gaps between the spray foam and the back of the drywall can make a highway between penetrations.  The air barrier needs to be tested before the drywall is installed so that foam imperfections can be corrected.

• Use AeroBarrier: This is a waterborne acrylic sealant that is sprayed into a pressurized space, using the pressure to guide the sealant into any cracks or crevices.  The process can be applied pre- or post-drywall with any type of insulation.

• Using drywall: if you skip an air barrier membrane, you can use the drywall itself to make an air barrier.  The most problematic areas are the joints and penetrations, which can be addressed using the right materials.  You’ll need special electrical boxes, gasket material, expanding foam, flexible caulk and adhesive; here are 2 articles on what to consider and how to hang airtight drywall. 

• After drywall: it’s not ideal, but you can still make major sealing improvements after your home is “finished”.   Start by doing a visual check for daylight or artificial lights around the door and window perimeters when they are closed.  You can use your hand or a candle to find air leaks and drafts as well.  Check under sinks and behind appliances like refrigerators and gas stoves for wall penetrations that have not been sealed.  Once you’ve sealed as much as you can with foam (be careful using expanding foam), caulk, and weatherstripping, call in an energy auditor to do a “blower door test” to see what you may be missing.  They should be able to tell you how leaky the home is in terms of “Air Changes per Hour” (ACH), and suggest and/or perform other remedies to lower the ACH, making the home tighter.

Because of the continued increase in interest for air-sealing homes and businesses, there is an Air Barrier Association of America (abaa.org).  The association is “committed to educating the public about air barrier systems and developing a professional air barrier specialty trade and industry dedicated to the installation of effective air barrier systems in buildings on a nationwide scale.”  Here are some of the resources they have:

• Here are some of the systems they’ve tested for air barriers.

• You can search for a specialist in your area here. 

• Courses for installers, auditors, and whole building airtightness technicians (with applicable fees but open for anyone to take)

Air-sealing your ducts for better air quality and energy savings 

In our post “How does indoor air pressure affect ventilation and air quality?” we show a photo of a room being aerosol sealed from the inside out.  This is a great way of closing up the small leaks (up to ½” diameter) that are overlooked by design flaws or construction crews, in order to seal the home’s thermal barrier before finish work on the home is completed.  Here’s how this innovation started: duct sealing.

Before rooms were sealed from the inside out by aerosol sealant, the process was developed for air ducts in 1993.  In one case study by AeroSeal, the innovator and major supplier for this technology, a homeowner had her ductwork expanded to cover previously unserved areas of her home.  After the new ductwork was installed, the system was pressure-tested and it was discovered that air of about 919 CFM (cubic feet per minute) was leaking through the ducts, which is the equivalent volume of about 551 refrigerators per hour(!).  According to energystar.gov, “about 20 to 30 percent of the air that moves through the duct system is lost due to leaks, holes, and poorly connected ducts.”  (To put this in perspective, the average system is 3.5 tons.  A system is required to have 400 cfm per ton of air across the evaporator coil for cooling, thereby 1400 cfm is the normal flow of the average system.  Twenty percent (280 cfm) to thirty percent (420 cfm) would normally leak from the ducts, so this homeowner either had a much larger home, or exceptionally leaky ducts.  In any case, after sealing the ductwork, a 91% reduction in leakage was realized.  Consequently her sinus issues were relieved and she felt more comfort in the home.  The system was previously drawing in dust and contaminants from outside the home and recirculating them in the HVAC system; apparently this problem was relieved by sealing the ducts.

The following diagram shows how air leaks into and out of ductwork (aeroseal.com):

The home is in heating mode shown by the orange ductwork coming out of the furnace in the bottom right.  Ductwork farther from the furnace turns blue (cooler) because pressurized, heated air is leaking from the ducts into the crawlspace and void spaces, before it even gets to to the farthest room.  For air quality purposes, the most important part of the system is the return areas, in the ductwork in the attic of this house.  Because the air pressure inside return ducts is negative (it is being “sucked” or drawn back to the furnace by the fan), any leaks in this area will cause dusty, unconditioned air from the attic or voids into the ductwork (see green arrows entering the ductwork in the top of the picture).  This is one major cause of excessive dust and poor air quality in many homes.  Even more leaky are the ducts in many multi family homes and apartment buildings.  AeroSeal has been successfully used in these buildings since 2007-8.  

The sealant used by AeroSeal is a “water-soluble organic compound” (AeroSeal FAQs) with an extremely low concentration of VOCs.  The sealant smells like Elmer’s glue when wet, but dries to be odorless. The safety data sheet reveals it to be a “vinyl acetate copolymer” (35% max weight) and “vinyl acetate monomer” (<0.01% when dried).  In accordance with California Prop 65, the product “does not contain any chemicals known to the State of California to cause cancer, birth, defects, or other reproductive harm.”  According to the EPA, vinyl acetate definitely has exposure limits due to irritation of upper respiratory tract as a result of acute or chronic exposure.  Due to this information, it’s possible that very sensitive individuals could have a reaction with the dried substance in their ducts, so it may be wise to ask for samples before it’s applied in the home of sensitive individuals. 

Aeroseal is not the only duct-sealing product on the market.  Here are some other options:

• Aluminum duct tape is available online and at most home improvement stores and can be used by anyone.  

• Ductwork mastic should be applied over the aluminum duct tape. It gives extra strength to the seal and encloses any seams of the tape.  It’s applied by paint brush and is usually water soluble (soap and water cleanup).

• Spray Mastic products: These are typically products for professionals because of the spray equipment needed to apply them. 

• Spray-Seal by Carlisle is a sealant applied to the exterior of ducts (especially hard ductwork) manually either after fabrication or as an upgrade to existing ductwork. 

• PROseal Spray by Ductmate Industries Inc. is a sprayable mastic sealer which is also applied by professional spray equipment.  

• Duct-EZ is a water-based zero-VOC mastic that is not only used to seal ductwork; it is also used to seal cracks in your foundation or basement to reduce seepage of radon into your home.  

Since dust is a major contributor to indoor air pollution, the dust may indeed be coming from the attics and crawlspace, and/or directly from the outside through building envelope cracks and crevices.  Before contracting for a duct-sealing service, it would be wise to have an energy audit on your home performed in order to discover the most economical ways to seal the largest leaks.  

What are ultrafine particles and where do they come from? 

In our post “Which particles can get captured by a filter or by my lungs?”, we mentioned ultrafine particles, which are classified to be 0.1 micron or less in diameter.  They are called UFPs (ultrafine particles) or PM0.1 (Particulate matter 0.1 microns), and are dangerous to our bodies in a different way than PM2.5 (Particulate matter 2.5 microns) , because they can migrate from the lungs or respiratory pathways to the rest of our bodies.  Their movements and concentrations are also different.  Learning about them is a good defense for avoiding them, though, so here’s some of what we know.

• PM2.5 consists of a mixture of particles of varying sizes from a variety of sources, with the most numerous particles by count usually falling within the ultrafine size range (<100 nm).  
• UFPs are mainly composed of organic compounds, elemental carbon, trace metal oxides, sulfates, and nitrate ions (2012 and 2016 studies). 
• Among the sources of emission, heavy industries are considered one of the largest anthropogenic sources of trace metals (2012, 2014 and 2017 studies)
• UFPs are unstable.  They have positive, negative and neutral charges,  and become larger particles through coagulation (when two or more particles combine) and condensation (when additional vapors can condense on the particles) (Jan 2022 overview). 

UFPs can be emitted by a number of sources.  

Source: overview study of UFPs

Since Natural Sources are largely not controllable, let’s focus on the anthropogenic sources (originating from human activity). 

Vehicular, aerial and sea traffic:

Airports: it’s estimated that in the United States ∼40 million people live near 89 major airports (i.e., within areas with ≥45 dB noise levels near airports) (study).

Aircraft exhaust is the #1 pollutant at major airports, and neighborhoods surrounding the airports even 10 miles away have higher ultrafine pollution levels.  According to a 2014 study, the “level of pollution at LAX (Los Angeles International Airport) was equivalent to the emissions generated by nearly 500 vehicles stalled in freeway traffic every day.”  Another study in 2018 in the Boston area measured particle numbers (PN) indoors and outdoors.  PN overall indoors was compared during times of impact-sector winds (during prevailing NW or SW winds) to calmer conditions; during impact-sector winds, the indoor measurements were about 1.7 times that of calm conditions.  We know that particles infiltrate homes via cracks in the building envelope, open windows, or forced-air ventilation, and this was shown through the study because outdoors and indoor PN levels usually increased and decreased in tandem, except for indoor events like cooking or cleaning.  Unlike road emissions, aviation emissions do not dissipate with higher windspeeds because of the buoyant nature of the aviation emissions.  This is the reason that some ultrafine particles, like wildfire smoke, can be transported in upper-atmosphere winds for thousands of miles.  Interestingly, significantly higher UFP emission per kg fuel burned resulted under landing conditions as compared to takeoff conditions. (2021 study)

HEPA filtration inside the homes helped somewhat; it lowered indoor PN by approximately 33%.  This is good, however, it didn’t have the same effect as lower number of flights or no impact-sector winds.  This causes us at HypoAir to continue recommending sealing homes to the best of our ability, and using controlled fresh-air ventilation for homes (via filters).  Ultrafine particles from airports are not currently regulated by the EPA, so we need to protect against them!

Vehicle exhaust: In many urban areas, vehicle exhaust is a major health concern. The following pictorial representation is found in the study “Chemical Composition of Quasi-ultrafine Particles and their Sources in Elderly Residences of São Paulo Megacity”

In urban areas with both aircraft and ground vehicle pollution, vehicle exhaust can be identified by larger particle size and higher BC concentration. (2021 study). 

Likewise, roadway emissions can be characterized by the fuel type, lubricants used, thermodynamic conditions, ignition technology, and the number of vehicles running.  This is why large cities have performed emission inventories in order to reduce particulates in certain ranges by certain types of vehicles.  National and local governments have devised three categories of strategies to control PM emissions: (1) fuel-based strategies, which include reducing sulfur levels; (2) engine-based strategies, which could alter combustion to reduce emissions; and (3) exhaust emission control strategies, which include the use of modern technologies, such as DOCs, diesel particulate filters (DPFs), and SCR catalysts, focusing on reducing emissions after combustion has taken place but before they leave the tailpipe. (2020 article).  New engines, paradoxically, emit more UFPs than older engines (1996 Health Effects Institute), but with these exhaust emission control strategies, UFPs can be captured before they are released.

Marine traffic: According to noaa.gov, 76% of all trade in the US involves some sort of marine transportation, and marine transportation touches 90% of all trade internationally.  Barges are extremely efficient transporters; what other mode can transport a ton of cargo 647 miles on 1 gallon of fuel?  In comparison, trains move 1 ton at 477 miles per gallon, and trucks at 145 miles per gallon. (2017 article).  However, the sheer number of tons of cargo moved on ships and barges necessitates huge quantities of fuel and emissions.  The International Maritime Organization (IMO) mandated lower sulfur contents in marine fuels beginning in 2020, at max 0.5% sulfur down from 3.5% previously for heavy fuel oil (HFO).  This cap caused many ships to start using intermediate fuel oil (IFO) or other lighter fuels instead of HFO.  The sulfur cap is a step in the right direction for less sulfur in the environment, but it was not expected to reduce UFPs (in terms of Particle Number or PN) from shipping sources.  The total output of PN from marine shipping in 2016 was similar to the total anthropogenic emissions in continental areas.   Thus, marine traffic is a significant source of UFPs (2021 Environmental Science & Technology article).

A third major source of outdoor anthropogenic UFPs is from coal-fired power plants, which produce emissions that are particularly rich in metals. You can access a map of US power plants here (gas, oil and coal), that gives type of fuels, emissions, and demographic information of the surrounding area.   Many plants may filter their emissions to meet standards, however UFPs can form outside of the stack when SVOCs condense (gasses turn into solids and thus bypass the filter). (2020 article) This process is called nucleation.  The most persistent UFP sources in the low atmosphere near the surface are modern technology fossil fuel-burning power stations, refineries, and smelters, according to a 2018 study. 

A fourth major source of outdoor UFPs is from wildfire smoke and controlled burns, which can vary significantly depending on the type of wood burned and its moisture content.  Wildfires can also smolder for a long time after being “extinguished”, and this smoke contributes significantly to the total wildfire emissions. 

Indoor UFPs are a combination of what has leaked into the house from the outdoors, and what is generated indoors.  Cooking and cleaning are large contributors, as well as candles, incense, smoking and e-cigarettes, and (in unconditioned climates) mosquito coils.  The use of e-cigarettes by children and young adults is unfortunate because their lungs are more susceptible to damage from UFPs.  Also, if you have a laser printer, it is surprisingly one of the major contributors to UFPs in offices (and homes!).  

Toxicological effects from exposure to UFPs; Jan 2022 overview

Here is what happens when our bodies encounter UFPs.  They are normally inhaled (effects via mucous membranes, skin and eyes are much smaller). The larger particles (10 microns and larger) can be trapped and removed via the mucous system, but smaller particles (2.5 microns and smaller) may be trapped in the alveoli and terminal bronchioles.   UFPs go into the deepest parts of the lung, and the body’s cellular defense system is activated.  This includes macrophages, various cytokines, chemotoxins and leukocytes, including neutrophils. Some of these are involved in the body’s inflammatory response, which not only damages the invading substance, but is also detrimental to the body in chronic doses.  

The UFPs can translocate to other organs such as the brain, liver, kidneys, and because they are fat-soluable, also deposit in adipose tissue. The body’s production of oxidizing species places oxidative stress on the body, which can cause damages to the DNA and mRNA, and lead to cancer.  Even transgenerational changes to DNA can (occur through inheritance!  

The toxicity of UFPs depends on a number of factors, including:  

• The age and health of the person affected (children are most affected, followed by the elderly and pregnant women). 
• The emission source, which determines the makeup, characteristics, size and concentration of the pollutants.  For example, black carbon (BC) is one combustion pollutant made up of PM2.5 and UFPs, but it is more harmful than other PM2.5 because of the body’s inflammatory response to it.  Black carbon can also adsorb other toxins before it is inhaled, like VOCs and PAHs (polycyclic aromatic hydrocarbons).  One study found that the smaller the particle size, the greater the inflammatory effects in the lungs, and the greater the DNA damage.  Another study found a positive correlation between the concentration of UFPs from motorcycle exhaust and the physical of damage to mice kidneys (neurological effects, memory loss,  behavioral problems and changes in brain tissues are other effects). 

With all the sources inside and outside, it seems that UFPs are unavoidable in daily life!  They are everywhere, but here are our top tips for keeping them out of your home and your body:

1. Seal up your home as tightly as possible, and use controlled fresh air ventilation through a MERV 13 filter* (see chart below) and your home’s HVAC system.  Balanced ventilation (as opposed to negative pressure ventilation) has less chance of suctioning combustion exhaust from gas appliances such as gas dryers, water heaters and furnaces.  
2. In addition, use a HEPA filter in your home to capture UFPs that are generated in the home or slip past the ventilation filter. 
3. Bipolar Ionizers like those in HypoAir’s Germ Defender, Air Angel or Whole-Home Polar Ionizer help to cluster ultrafine particles into larger particles that can fall out of the air or be captured in a HEPA filter.
4. Use stovetop ventilation during and after cooking and bathroom ventilation during and after showering.
5. Don’t smoke or vape (use e-cigarettes).
6. Use a HEPA mask (outdoors or in a separate ventilated building if possible) during high-risk activities like welding, spray painting, sanding or woodburning and 3D printers. 
7. Don’t allow vehicles or gas engines like generators or lawn mowers to idle in the garage.  
8. If you move, reconsider locations with high UFPs such as downwind of airports, refineries, power plants, bus stations, major highways, etc. 

*Here is the reason we recommend MERV 13 for ventilation filters:  it increases capture of small particles to include that of smog, tobacco smoke, and cooking fumes. 

Above diagram from pureairfiltersdirect.com

Which particles can get captured by a filter or by my lungs?

This is an incredibly important and somewhat complicated question.  I want to present the following graphic, which shows relative particle size.  I’d say it’s pretty surprising how large our hair is and how small those bacteria, smoke particles and viruses are, right?  The “µm” stands for micrometers, which is one-millionth of a meter.  Micrometers are also called “microns”, so the human hair is 50-180 microns.

In our FAQ on “What is HEPA?”, we explored how filters actually trap contaminants like these.  In order to start answering our original question, let’s review that!

“Sieving” is the most simple way a filter “strains” out the particles that are larger than the openings between the fibers of the filter.  

                  (image from classicfilters.com)

Then, there are three types of motion that particles experience in a stream of air, such as the airstream being drawn through a filter.  Filter design actually takes advantage of the size of particles and the way they move through the air, in order to capture them.  

• Obviously, some particles are larger than others.  Inertia acts on larger particles by causing them to continue in their original path of motion when entering the filter, thus colliding directly into fibers instead of sweeping around them with the accompanying airflow.  Particles 0.3 micron and larger (coronavirus size and larger) are affected by inertia. 

                (image from classicfilters.com)

• Air is made up of all kinds of molecules and particles, which are getting thrown about in erratic ways by collision with one another.  This is called Brownian motion.  Taking Brownian motion into consideration is filtering by diffusion, which occurs when smaller particles travel in an erratic fashion through the airflow and are impeded by fibers.  The particles trapped by diffusion are typically smaller than 0.1 micron.

                         (image from classicfilters.com)

• In direct interception, a particle follows the airstream but travels closer than its radius to the fiber, “brushing” it and becoming stuck.  This can happen for many different sizes of particles and just depends on where they are in the airstream relative to the fibers.  

                    (image from classicfilters.com)

So there you have it– four ways a filter uses to capture particles.  Interestingly, because of the gap between inertia and diffusion, particles around 0.3 microns in diameter are the most difficult to filter out of the air, because they are least affected by these methods.   This is called the most penetrating particle size (MPPS)--the size that is most likely to slip through the filter.  

HEPA filters are rated on their ability to remove this size particle—0.3 microns.   They do so with greater than 99.95% efficiency.   There are 2 ratings of HEPA: H13, which removes at least 99.95% of 0.3 micron particles, and H14, which removes at least 99.995% of 0.3 micron particles.  

Without a HEPA filter in your home, you are probably relying on furnace filters of various lower filtration ratings.  That means that more particles are getting through the filter, and remaining in the air for you to breathe.  Yikes!  Particles of 10 microns or less can be inhaled, and particles of 2.5 microns or less are more likely to deposit deep in the lungs.  (California Air Resource Board).  This size of particle is extremely lightweight, and once it’s in your lungs, it can move all the into the deepest part of your lungs and lodge there.  Without filters to capture particles from the air, unfortunately your airway and lungs will act as filters.  Here is how (Canadian Center for Health and Occupational Safety):

• The respiratory system can be divided into upper and lower regions.  The upper region starts at the nose and mouth, and goes down to the vocal cords in the larynx. The lower region starts at the larynx and extends through the trachea all the way to the bronchioles and aveoli (smallest air sacs).

• Particles 10 microns and larger are most likely to lodge in the upper respiratory region by inertia (also called impaction), because in this region, air is flowing at a higher velocities and during the twists and turns particles tend to continue in their original direction and “impact” a wall of the airway and stick there.

• Interception is likely to occur with fibers, like asbestos fibers.  In the range of 1 micron in diameter and 200 microns in length, if one end brushes an airway wall, it will lodge there.  These can make it into the bronchial tree.

• Sedimentation occurs when particles larger than 0.5 microns loose their momentum and gravity takes over, causing the particles to settle in the bronchi and bronchioles.  

• For particles smaller than 0.5 microns, diffusion is in effect (Brownian motion).  This can happen in the small airways and alveoli, when air has virtually slowed to stillness.  

• Although the mucous lining of our respiratory tracts was designed to clear airways by moving it up and out of the respiratory system, it does not always function well in older and diseased people, and the sheer number of ultrafine particles can clog airways. 

Fine particles (2.5 microns down to 0.1 micron) and ultrafine particles (0.1 micron and smaller) are shown to cause inflammation and inflammatory diseases.  Ultrafine particles can migrate from the alveoli to the bloodstream and to other organs, resulting in delayed sicknesses such as reactions to vehicular pollution, welding fumes and burning trash.  The danger of ultrafine particles is not just their size and number (much greater numbers PM2.5), it is also their charge, which can adsorb toxic chemicals onto their surface.    Fine particles have been shown to cause cardiovascular disease; they travel up the olfactory nerves to the brain; they are inhaled by electronic cigarettes, and have been shown to increase risk for hypertension and diabetes and cause cancer (animal studies) . (study)

For all these reasons, a HEPA filter is a great addition to your home, vacuum, and even a mask when you are performing high-risk activities like welding, spraying paint, or caring for a sick relative, so that the filter will do the work instead of your lungs and body!

How is my Crawl Space affecting my Indoor Air Quality?

According to the National Association of Home Builders, 65% of new homes in 2020 were built on slab foundations, 22% had a full or partial basement, and 12% had a crawl space.  From their statistics since 2000, it’s clear that slab foundations are increasing, while basements and crawl spaces are decreasing.  From an indoor air quality perspective, we have to admit that’s a good thing!  We found a lot of other pros and cons about slab foundations, and if you are building or buying a home and have a choice, you should investigate the differences.

Slab foundations became popular in the 1950’s; before that, most homes were “raised” with a crawlspace or set over a basement.  Crawl spaces did their job to keep the main living area “off the ground”, ie. not in direct contact with the earth, and they accommodate floor plan renovations more easily than slabs because of easier access to plumbing.  However, crawl spaces typically are partially sealed off, and very contaminated with dust, mold, bacteria and stale air.  What you did not know about crawl spaces may be the most harmful of all: “Approximately 50% of air on the first floor of your home comes from your crawl space.” (goTerraFirma.com)  How can this happen?  Due to the stack effect which affects virtually every building on the planet, warm air rises through the house and is replaced by cooler air from outside, through leaks in the lowest parts of the home.  If you have a crawl space that is partially open to the outside, you may even place a pinwheel or light tissue in the crawlspace opening on a still (non-windy) day, and see if the air currents are blowing into the crawlspace of your raised home.  Fresh air from outside will be drawn into the crawlspace, pick up dust, mold and bacteria (not to mention musty or animal smells), and infiltrate your home through leaks in the flooring.  Gross!

If you can’t or won’t investigate the condition of your crawl space first hand, find a foundation expert and ask them to conduct a thorough inspection (with photos).  Knowledge is the first step to preventing or remediating the problem!  Here’s what they may find:

• Flooding.  Just like any other ground that floods, if water enters your crawlspace, it can pool and remain for weeks or months, depending on the environment and soil composition.  How about living over a stagnant puddle?
• Moisture damage.  Moldy and rotten timbers are a consequence of constant water contact and high humidity.
• Insect damage.  Termites can thrive in even lower moisture zones, and without proper termite prevention like physical barriers, they can do a lot of damage.  The shredded wood creates even more dust under the house.
• Animals and animal damage.  There are several harmful aspects of animals living in the crawl space under the house.  For one, their feces can carry virulent diseases like hantavirus (from rodents).  Then, unfortunately they may die under the house, with accompanying death smells and a bacteria-laden carcass… Third, they may actually undermine the foundation with burrows.  Did you know that groundhogs can seriously impact your home’s foundation, causing sagging floors and major structural problems?
• Damaged and missing insulation.  Exposure to water, insects and animals all results in deterioration of insulation on pipes, ducts and subfloor, so that the essential systems and floor itself are exposed.  

If you have a crawl space and want to improve indoor air quality, don’t miss this opportunity to take a step in the right direction by hiring a trusted professional to do an inspection, and then get several bids for remediation.  Most foundation companies will recommend a combination of the following to resolve these issues (from GroundWorks.com):

• Encapsulation is a method of sealing off the crawl space from the surrounding elements.  It involves closing crawl space vents, installing a vapor barrier so that moisture from the ground does not intrude, and installing a dehumidifier.
• Insulation is important to prevent condensation and resulting mold issues.  Damaged insulation should be replaced and missing insulation should be installed.
• Sump pumps are necessary if standing water has been a problem in the past, and to remove condensate from the dehumidifier.  
• Repair of sagging and damaged joists and supports.

It may seem like a daunting task, and these tend to get postponed until things get really bad.  If you don’t know the condition of your crawl space, we want to encourage you to take a first step of inspection, which many companies do for free.  If remediation is required, call several more companies for inspections and quotes, and research their work.  When the work is completed, you will have the comfort of protecting your largest investment (your home) and increasing your air quality at the same time.  It’s hard to overestimate the cost of a less humid, healthier, fresher home! 

How can I make sure my basement has good air quality?

If you glanced at our post on crawl spaces, you would know that more new homes have basements than crawl spaces, but they are both declining in popularity.  Here’s what the National Association of Home Builders found:

Still, many existing homes have basements, finished and unfinished.  They can add value to your home value by boosting its square footage and livable space, or they can be a detriment to your home value as a source of mold and poor air quality!   Let’s hope that your basement falls into the former category…but read on to make sure!

The basement shares several characteristics with the attic: many times they are not planned to be living space, and thus often lack the proper ventilation and fresh air flow.(ecolivingexpert.com)  Also, they are often made to be storage spaces containing boxes (cardboard is food for mold and many types of insects and pests), and then home heating systems are often installed there, which if they are gas- or oil-powered, have the potential to leak fumes.  

Whether you use your basement as living space or not, the basement has to be maintained with proper ventilation and dehumidification so that it doesn’t contaminate the rest of the house with poor, even dangerous air quality.  Let’s take a look at these problem areas and sort them out one by one!

Radon is a concern in many areas of the country.  It’s a colorless, odorless gas that that seeps naturally from certain underground rocks and can permeate basement walls and foundations, as well as contaminate ground or well water.  Because radon is radioactive, it can cause cancer (it’s estimated by the EPA to be the #1 cause of lung cancer among non-smokers).  Radon tends to accumulate in basements because it’s heavier than air, so it’s best to have the basement checked for radon levels, and if present, investigate mitigation systems (you can find local qualified contractors through the link on this page, and information on water testing labs here). 

Moisture and mold: If you smell an earthy, musty smell in the basement, it’s most likely mold that is starting to form or has already formed.  The smell is characteristic of the Microbial Volatile Organic Compounds (mVOCs) that the mold releases.  Some MVOCs have been identified as irritants and can contribute to sick building syndrome (easlab.com).  The key is to identify the area (possibly many areas and the whole basement) and remediate in order to stop the growth and get rid of the mold, as soon as possible.  Here are ways to do it:

• Ventilate: Although opening the windows of the basement, if you have them, will help dilute the smell, it will not stop the mold from growing and continuing to produce mVOCs.  Ventilation has to be done with dehumidification (next point), eliminating excess moisture, in order to stop the growth of mold.  Ventilation can be accomplished by a dedicated basement ventilation system (check out EZBreathe), or by installing air vents from your existing HVAC system to ventilate the basement, creating a positive pressure in the basement.  Although installing a return air vent in the basement could utilize the coolness of the basement to lower AC energy costs, if you have a mold problem in the basement, this is not a good idea as it can distribute the mold spores through the rest of the home. 

• Dry it out: Check that any water pipes running through the basement area or behind its walls or ceiling are not leaking or even causing condensation.  Cold water pipes from a well or underground can easily cause condensation to form, leading to…you guessed it– mold!  Drying them off and adding insulation can solve this problem.  If there are no leaking pipes, condensation, or flooding issues, then moisture from the surrounding earth can be permeating the block walls of a basement, because concrete is porous.  (For all of my childhood, I lived in a neighborhood called “Spring Hill Estates” because it had springs, one of which was a constant source of moisture for our basement.)  It’s possible that the humidity can be lowered by running a portable dehumidifier, which should be run to a permanent drain (sink, shower or other drain) in order to avoid shut-off or accidental flooding issues.  Alternatively, there are numerous foundation and basement repair companies which can inspect and suggest drying solutions to keep the basement at a proper humidity (30-60%)--the drier the better!  Don’t wait on calling several firms for inspections and quotes, as these are normally free of charge.  

• Add some active air purification like Air Angel, a purifier that zaps mold spores using 3 technologies for more breathable air.  A standalone HEPA filter is also recommended to filter out mold spores (alive or dead) with an activated carbon element to remove mVOCs and smells.

• Get rid of “consumables” like cardboard: Side story: I was sorely disappointed to walk into my storage building at the beginning of summer and find an antique portable sewing machine case (which was covered in a clothlike material) streaked with mildew.  Similarly, if you have to use the basement for storage, plastic tote containers or vacuum bags are way better at resisting mold and protecting the items inside from moisture and insect damage than cardboard. Try to store containers on shelving with plenty of ventilation under and between them (like wire shelving) instead of stacking them on the floor or against each other or a wall.  If antiques are valuable to you, try to make room for them in your normal living area, where the humidity is more controllable.  Also, furniture that is made of “pressboard” can absorb more moisture than real wood, with less options for cleaning and disinfecting it.  The use of scatter rugs rather than wall-to-wall carpeting allows for easier washing and cleaning of the floor if it has moisture issues, too.  Consider using hardwood or plastic blinds or shutters for windows instead of draperies, which can absorb moisture. 

Combustion fumes: If you are intentionally or unknowingly using a “negative pressure” ventilation system in your home, exhaust from a gas, oil, coal or biofuel (like wood) furnace can be extracted out of the appliance’s exhaust system if it’s not well-designed or sealed.  As we reviewed in the post “How is my crawl space affecting my indoor air quality?”, the stack effect causes warm air to rise through a home and exit through the roof or attic, drawing cool air into lower levels of the house.  The rise of the hot air creates a slight negative pressure on the lowest levels, like a crawl space or basement, drawing in outside air and even extracting combustion fumes from a furnace into the air.  This can create an extremely dangerous mixture of VOCs that spreads through the rest of the home with the air flow. 

Chemicals, paints, batteries and cleaning products: We get it, these are the substances you don’t want anywhere near your pets or children, so the basement seems like the perfect space to seal them up and store them away!  It is okay to store them there, but only if they are truly sealed (hammer to the lid of the paint can or transferred to a more sealable container with a screw top) AND humidity/moisture is under control AND they are not overly old, so that metal containers do not rust.  Due to external or internal moisture, I’ve seen metal paint cans rust completely through the bottom, and then I’m left with a gooey, toxic mess!   The best scenario is to dispose of old paints and chemicals safely; most communities have a toxic material disposal site or a designated day to bring them to the regular garbage site.  It’s just safer to have these things out of the house!  If you use the basement as a hobby space, make sure to have the proper exhaust ventilation.  The stack effect can drive fumes from glue and paint and dust like sawdust particles, right up into the house.  

Install an air monitor to help take the guesswork–or legwork–out of knowing if the dehumidification and purification is working.  Thanks to wireless technology, you don’t even have to open the basement door to know if pollutants are elevated.  AirThings’ View Plus monitors all the important conditions of a basement: radon, PM2.5, CO2, humidity, temperature, VOCs and pressure (if they had to add anything, CO would be helpful for spaces with combustion appliances like gas furnaces or dryers).  Their connectivity to the app on your phone makes it easy to check!  Kaiterra’s Laser Egg + Chemical is a close runner-up that monitors Total VOCs, PM2.5, temperature and humidity (it doesn’t do radon or CO).  Either of these monitors will help you “see the unseen” air quality of your basement.

Your basement doesn’t have to be scary because of mold and poor air quality.  Shed some light on the subject by doing your own inspection, and if it seems overwhelming or the solutions you try are not working, get professional help.   The health of your family and home depend on it!

How to lower humidity in your home by choosing the right dehumidifier

If you have incorporated a humidity sensor or two into your home and monitoring routine, bravo for you!  We at HypoAir believe that these are among the most important tools you can have in your air quality toolbelt.  Now, what you do with that information–home or room humidity–-is equally important!  If the monitor tells you that a space is consistently above 60% relative humidity, after you’ve checked and mitigated the sources of moisture (see our post “Humidity and an Indoor Moisture Inventory”), then a dehumidifier can bring it down into the 40-60% range.

The great thing about dehumidification is that by reducing the humidity, you are also increasing comfort.  In hot climates, excess humidity in the air prevents our bodies from cooling effectively by evaporation, because the air is already loaded with moisture.  In cold climates, excess humidity in the air (such as in coastal regions) causes us to feel colder than in dry air at the same temperature.

You are also saving on energy usage for 3 reasons:

• Air conditioners use less energy to cool dry air than more humid air at the same temperature, and heaters use less energy to heat dry air than more humid air at the same temperature.
• In the summer you will feel cooler at any given temperature, when the air is drier versus more humid.  Therefore, you may be able to set your thermostat higher during the summer!
• In the winter you will feel warmer at  any given temperature, when the air is drier versus more humid.  Therefore, you may be able to set your thermostat lower during the winter!

Dehumidifiers come in all sizes for all applications.  When choosing a portable one for a room, it’s important to know the following things:

• Square footage determines capacity:  Just like air purifiers, dehumidifiers are limited by air flow, so standalone units can’t effectively dehumidify through walls and doors.  If you are choosing a standalone unit, measure the floor space.  The square footage measurement incorporates standard 8-foot ceilings, because it really translates to air space, which is ft3.  For 500 ft2, start with a small dehumidifier (10 pints for a moderately humid space and 12 pints for a more humid space) and add 4 pints capacity for every additional 500 ft2 (bobvila.com).  The capacity is usually measured in pints or liters per day, which is the amount of moisture the unit can draw from the space in 24 hours.  The Department of Energy changed capacity testing and ratings for models released in 2020, so newer models are not comparable to older ones.  This page shows a table comparing older and newer capacity ratings.
• Additional/ongoing moisture sources:   Human occupancy = moisture!  We sweat, breathe, and generally exude H20, and rooms with higher activity or temperature levels (like a home gym or sauna) will need more dehumidification capacity.  Also, leaks in the building envelope like doors and windows can allow moisture from outdoor air to come in.  Then, there are those inherently humid spaces that incorporate running water like bathrooms and laundry rooms.  
• Energy Efficiency:  Dehumidifiers are very much like air conditioners, with similar parts and operation.  A coolant is pumped in a closed loop system from the hot side (condenser) to the cool side (evaporator) to draw moisture from the air, collecting it in a reservoir or allowing it to drain to a permanent drain.  The compressors in these dehumidifiers used to draw significant energy (amps) to do their work of changing the fluid from gas to liquid, but newer models are much more energy-efficient.  Inverter technology decreases the energy draw most of all, because the compressor will have a variable speed motor, allowing it to run continuously at a lower speed to keep a constant humidity, or ramp up when the humidity increases.  
• Method of dehumidification:  There are two main types of dehumidifier: refrigerant and desiccant.  Refrigerant is by far the most applicable to residential needs because it can remove large amounts of water from rooms above 50 degrees F.  These work when humid air is drawn across the cold evaporator coil containing refrigerant; the refrigerant removes moisture from the air and produces condensate, and the dry air is blown into the room.  Desiccant dehumidifiers work in lower, less humid spaces by absorbing water directly into a material (desiccant), which is dried out to be used again.  There are some desiccant humidifiers on the market for small spaces like closets or cars; these require that the desiccant be regenerated in an oven or replaced with new desiccant. 

Installing a portable refrigerant dehumidifier is pretty simple; you will need to: 

• Place the unit in the room you want to dehumidify (not inside of a closet), at least 1 foot away from walls or other obstacles so that air is free to circulate around it
• Make sure it’s placed on a flat and stable surface. Sometimes carpet can be too plush for this purpose, so try to find a board or other flat surface
• Choose your drainage method (ideally you should have this in mind before selecting the unit).  If using the bucket, make sure it’s properly installed (most new units will not start working if it’s not).  If using continuous drainage, make sure that the hose is attached securely, the drain end is placed into a sink or drain, and check for leaks once it starts to operate.  Unless the dehumidifier has a condensate pump included, the drain hose end will need to be lower than the unit so that water doesn’t back up in the unit.
• Plug in and set the desired humidity level.

If you have a humidity problem in several rooms or the whole house (this is common situation in hot, humid regions), it’s wise to choose a whole-home dehumidifier. This is a permanent installation that uses your home’s HVAC ducts to distribute dry air throughout the home.  Whole house dehumidifiers are a bit complicated (not generally a DIY installation) essentially involving hanging the unit, running the ductwork, running the condensate line, connecting the unit to an electrical supply and installing the controller.   In addition, you need to make sure that the ductwork is connected to the right places: having a dedicated “return” vent for the dehumidifier, and sending the dry air to the distribution plenum for your AC, are critical for getting the most out of this unit. (pvhvac.com, bobvila.com)

One slight drawback of dehumidifiers is the heat that they produce.  Unlike air conditioners, the hot and cold sides of the heat transfer system are not separated by a wall, so the heat generated by the unit goes into the air surrounding it.  Unless the unit is placed in a small room, this usually doesn’t make a noticable difference in the temperature of the space, but it’s something to take into consideration.

Dehumidifiers need maintenance, just like HVAC units.  With standing water inside, mold can grow fast.  Some manufacturers require that the maintenance on whole house units is performed by a qualified HVAC technician, for warranty purposes.  Here is in essence what they do:

• Turn off the power
• Clean or change the air intake filter
• Clean the condensate drain line and/or add anti-microbial agents to the line
• If there is a condensate pump (typical in crawl space units), make sure it is clean and operating properly
• Make sure that the house humidity is staying in range of its setpoint

For portable dehumidifiers, you can do the following (cnet.com):

• Unplug the unit
• Wipe down the outside
• Empty and clean the bucket thoroughly with dish detergent.  If your unit is plumbed to empty the condensate into a garden hose or other hose line instead of the bucket, then unscrew the connection at the unit and use a towel to wipe any slime from inside the fitting.  Also at this time, you can dump a cup of vinegar or hydrogen peroxide (not both!) into the hose so that any algae forming in the line will die and be flushed out.
• Remove and check the bucket filter (if your unit has one) and clean it out.
• Rinse off the air filter
• Replace the bucket and air filter, and you’re good to go!

Dehumidifiers work best with air circulation!  With portable units, that means that using a ceiling or portable fan to move the air around the room, so pockets of drier or more humid air don’t form.  With a whole house dehumidifier, the fan inside the unit (if operating independently) or the HVAC fan will provide the circulation.

If you decide to invest in a dehumidifier, be sure to check the Department of Energy’s Buying Guide for additional tips, and to find Energy Star Products and rebates ($!)

To Vent or not to Vent the Attic?  It’s all about air-sealing and insulation

In the early 2000’s, this was not a relevant question for most homebuilders.  Attics were virtually always vented, in line with the thinking that ventilation was the best way to mitigate condensation and moisture issues, ice dams and other damage.  Like many elements of home design, however, practices have evolved to seal homes more tightly against energy loss and pollution.  Sealing the attic is one such evolution. 

In our article “On a home hunt?  Make sure Air Quality is on your home inspection list!”, sealing the attic was mentioned.   If you are building a new home, you will basically need to decide where the thermal boundary will fall–will it exclude the attic, or include it?  Here is a diagram to show what we mean (source: basc.pnnl.gov)

The pink lines indicate where insulation and air barriers will be.  In diagram a), the upper thermal boundary is located at the attic floor.  Notice that the roofline is broken at the eaves (small hooked part on lower ends) and there is also a “vent” in the ridge of the roof.  In diagram b), the upper thermal boundary is located at the attic ceiling (underside of roof), and there are no breaks in the roof line for vents.  Diagram a) will require that the attic is vented, but diagram b) will require that it is unvented.  Why?

Sealing up uninsulated spaces (like diagram a) will cause the air in the space to become the same temperature as the outside, but without ventilation, moisture cannot escape and mold and rot can form.  The alternative is to make sure the uninsulated attic receives plenty of outdoor air ventilation, OR include the attic within the thermal boundary, making it part of the “conditioned space” of the rest of the home (diagram B).  

Factors to consider when determining where to locate the thermal barrier in new construction include climate, desire for additional living and storage space, building design and configuration, and location of HVAC. 

Let’s explore the types of ventilation that are common in attics today (source: roofingcalc.com): 

Passive roof ventilation using:

• Ridge vents

• Soffit vents

• Roof vents including box vents and turtle vents

• Gable vents

Active roof ventilation using:

• Turbine-style (whirlybird) vents

• Motorized roof vents

• Gable fans

Many people are convinced that “if it’s not broke, don’t fix it”, and this applies to the traditional design of vented attics.  In truth, many attics have been able to ward off condensation, rot and mold for decades because they are well-ventilated and properly roofed.  If you decide to stay with a vented attic design and still keep the HVAC ducts in the attic, there are two developments that can help save money on heating and cooling.  

• Laying the ducts on the attic floor and burying them in fibrous insulation can achieve energy savings and can be done at any point, before or after building (although it’s easier whenever new ducts are installed) (basc.pnnl.gov) The key to success with buried ducts is making sure that the ducts are airtight, encapsulating them with foam (ccSPF=closed cell spray foam) if necessary, and deeply burying them in loose insulation.  Here is a diagram:

• If the ducts are hanging in your attic and you decide to keep the attic vented and ducts where they are, you can have them encapsulated in closed-cell spray foam in order to minimize heat transfer. 

Source: basc.pnnl.gov

Vented attics are not a good place for storage because of extreme heat, cold, and sometimes insect and pest issues.  Without the above measures, vented attics are also not the best place for HVAC systems, for the same reasons.  HVAC equipment will last longer and perform more efficiently when it’s operating in a temperate, dry climate.  Ducts passing through a vented attic must be sealed tightly in order to avoid pulling unconditioned air and dust into your home.  

The key to creating an unvented roof assembly is to keep the roof deck – the principle condensing surface in roof assemblies – sufficiently warm throughout the year such that condensation will not occur, or to prevent moisture-laden air from the interior of the home from accessing the underside of the roof deck. (basc.pnnl.gov)  This can be accomplished by installing rigid foam insulation over the sheathing, or (more commonly) using spray foam insulation under the sheathing.  Both require a high degree of air-tightness to avoid condensation.  In an existing home, changing the thermal boundary from the floor to roof or vice-versa can be quite a bit of work, and often it’s best to do/combine this task when reroofing or other modifications, like HVAC system replacement. 

For many people, it’s hard to imagine an attic that is not unbearably hot in the summer and frigid in the winter.  However, when the roofline is properly insulated and sealed to the walls, you have a space that is less dusty, easier to work in when renovations are made, and a better space for HVAC equipment.  It also provides a “buffer space” for all that conditioned air in your home, which tends to rise and escape through the ceiling area.  Without excess temperatures bearing down on your ceiling in the summer or trying to vent warm air in the winter, energy costs can be moderated.  If you do choose to convert to an unvented attic, be sure that the company you choose to seal and insulate it will do a thorough job of sealing, then apply sufficient spray foam insulation according to local code for your climate. 

Whether you decide to go with a vented or unvented attic space, the best choice for air quality and energy efficiency will depend on how well you can seal and insulate.  For vented attics, the living space below and any ductwork within need to be sealed and insulated from the attic space, which is an extension of the outside via ventilation.  For an unvented attic, the whole attic is an extension of your home and therefore must be sealed and insulated from the outside at the roofline.

On a home hunt?  Make sure Air Quality is on your home inspection list!

At HypoAir, we want to give you information that will help you make healthy choices about your existing home or any home you intend to live in (purchase or rent).  Real estate sites have a lot of pretty pictures, but until you step inside a home with critical eyes (and nose), you will not know the impact it could have on your life, because indoor air quality is even more crucial than the school district or neighborhood.  We hope that this checklist helps you make sure that all areas impacting air quality are assessed and addressed.

• Button it up.  It’s 2022, nearly 50 years after the energy crisis that stimulated a myriad of home insulation and building design changes.  If we’ve learned anything, it’s that insulation and sealant against air leakages is good.  The tighter the building envelope, the better air filtering and climate condition systems can do their jobs.  We list some of the points you can check, but for top energy savings, it’s best to hire a professional home energy consultant.  Certification varies by state, and here are two national pages that may help find a consultant: hersindex.com and US Department of Energy.  However, the best place to start looking for a Home Energy Auditer is with your local power company–some even conduct energy audits for free and install energy-saving equipment like lightbulbs for free.  If you need to hire an energy consultant, here are some helpful questions to ask: how do you discover the main air flow patterns in my home?  where will you target your time?  Can you address the discomfort during (winter/summer) in (name room).  What are the average savings homeowners realize with your services?  Energy consultants can perform a blower door test, and use infrared scanners and smoke tools to see the larger leaks that most inexperienced homeowners will miss.  According to energy expert Ken Gadsby, “doors and windows only account for 20-30% of air leakage in most cases”, while it is more cost and time effective to go after the other 70-80% that is coming from elsewhere. (from Solar Age article referenced here).   If you decide to do your own checks with equipment, you may want to buy a smoke pencil to find hidden leaks, you’ll want to find one that is not toxic. This brand uses glycerine, propylene glycol and distilled water to generate a non-toxic white smoke.  There are two main types of air leaks in buildings - direct leaks through the exterior walls or ceiling to the outdoors, and indirect air leaks through interior partition walls, ceilings, or stairwells and plumbing chases. (inspectapedia.com)  
  • Indirect leaks may be part of a larger convective air loop, where void spaces in walls and ceilings can pump warm air out of a house during the winter, or into a house during the summer.  You or the energy consultant may need to investigate penetrations such as ceiling lights and bathroom exhaust fans and uninsulated void spaces like ductwork, soffits (commonly above kitchen cabinets) and firewalls.  It may be that simply installing a physical barrier will interrupt the air loop and stop energy loss.  This can be done retroactively by drilling holes and using spray foam to seal cavities at the ceiling/floor level, sealing plates and void wall tops, etc.  
  • Direct leaks may occur around baseboard heaters, wall sockets and light switches (check out these easy gaskets), around window and door frames/molding, and around penetrations through exterior walls such as cable/telephone wires and gas lines.  These can be resolved with some low VOC caulk.  For larger penetrations like plumbing and drain lines, the only spray foam sealant that is UL GreenGuard Gold Certified is made by FOMO Products Inc., called Handifoam Window & Door.  Some penetrations, like electrical wires, may need a fireblock sealant by code, and Handifoam Fireblock is also GreenGuard Gold Certified.
  • Seal the attic: to vent or not to vent?  Attics are typically very hot or very cold, because the builder chose not to include this space in the conditioned space.  If an attic is insulated on the floor and interior wall boundaries, it will need to be vented so that it acclimatizes to exterior conditions and doesn’t hold excess moisture.  In the case of vented attics, according to the US Department of Energy, just a ¼” gap around the hatch (for a pull down ladder) is equivalent to a ceiling register removing heat from a room.  There are manufacturers of attic stair covers that can seal this difficult opening well.  Secondly, any air conditioning ducts in the attic must be sealed at all joints, which is something you may be able to do yourself.  As for the rest of the attic, this guide has details of all the places to check for undesirable ventilation.  On the other hand, if you live in a hot, humid climate, or want to reserve the attic for extra living space, then it’s wise to move the envelope to the roof line, and make the attic part of your entire’s home conditioned space.  Here is a page that will help you decide between venting and sealing the attic.
  • Seal the fireplace.   In general, it is the fireplace damper that opens or closes the chimney space to your firebox.  It needs to be closed when not in use, but if there is no damper, or it doesn’t seal properly, you can check out this page to decide how to seal it.  Just as importantly, the fireplace surround should be sealed to the stone or brickwork, and vents can be sealed off with magnetic covers.
  • Crawlspaces can be a source of home energy loss or increased heating bills, as well as mold and rot issues (inspectipedia.com)  The old recommendation was to thoroughly ventilate crawlspaces in order to prevent these issues, but now the recommendation is convert the crawl area to a conditioned space with vapor barriers and insulation.  Recognizing air leaks, humidity and mold issues in crawlspaces (and unconditioned basements) needs to be addressed!
• Not location, location, location: Ventilation, ventilation, ventilation!   Tight building envelopes without fresh air ventilation are unhealthy, and leaky building envelopes with the wrong types of ventilation also create problems.  Unfortunately, the average American home has no dedicated fresh air ventilation system. (buildinggreen.com) According to ASHRAE standards (formerly called the American Society of Heating, Refrigerating and Air-Conditioning Engineers), homes should receive 0.35 air changes per hour, but not less than 15 cfm (cubic feet per minute) fresh air per person (EPA.gov).  There are 4 types of dedicated mechanical ventilation; we discuss these in our post “How does indoor air pressure affect ventilation and air quality?”  Most home energy consultants recommend a balanced ventilation system that includes an HRV or ERV, however in hot and humid climates additional dehumidification will be necessary, because ERV’s actually raise the humidity level in your home.  
• Humidity.  If the interior stays above 60% relative humidity for long periods of time, it’s not a question of if, but a question of when, mold will become a problem.  Arming yourself with a simple humidity sensor on a home tour can confirm what your senses may already be telling you–does it seem too humid?  Or too dry?  Dry air can cause germs to live longer in the air, posing increased risk of respiratory infection.  You can do an inventory in your own home with our post “Humidity and an Indoor Moisture Inventory”, and HVAC experts in your area can help rectify under or over humidification with the right equipment.  The following graph shows the benefits of keeping it between 30-60%:

• Radon.  According to the EPA, radon is the #1 cause of lung cancer among non-smokers.  A colorless, odorless gas that seeps naturally from certain underground rocks, radon can permeate basement walls and foundations, as well as contaminate ground or well water.  It’s best to have the home’s air and water checked for radon levels, and if present, investigate mitigation systems (you can find local qualified contractors through the link on this page, and information on water testing labs here).  
• Mold.  As mentioned in our post “Taking our homes back from mold”, using a home inspector who is equipped with forward-looking infrared radar (FLIR) gives you “x-ray views” of hidden sources of mold.  FLIR is a type of thermographic camera that detects infrared radiation, and while it is used in military and spy applications(!), it is also extremely useful in locating areas behind walls where water intrusion may be present, making a hospitable area for mold.  Such a home inspector will also be intimately familiar with construction methods that can be causing moisture issues now or may cause them in the future. 
• Active Air Filtration and Purification.   Buttoning up the envelope and ventilating properly are non-negotiable basics; filtration and purification step up the breathability and comfort of your air.   Is the only air filtration in your existing or potential home done through the furnace filter?  If so, additional filtration and/or purification in the HVAC or standalone will help with dust, seasonal allergies, viruses, mold spores and mycotoxins, and pet dander. 
• Old House Materials.  Asbestos and lead paint are still out there in older buildings (pre-1978 for lead paint and pre-1989 for asbestos), and disturbing them will bring these hazardous materials into the air.  It’s best to make sure that your home inspector identifies any sources of these materials in case you get the (common) urge to renovate!
• Gas appliances.  Heartbreaking but vital information for foodies: gas stoves can throw quite a bit of VOCs and fine particulates (PM2.5) into the air, in addition to whatever you are cooking and what you are cooking it in.  If you plan on keeping or installing a gas stove, make sure that the ventilator hood is powerful enough for the space (check out our post ‘Humidity and an Indoor Moisture Inventory’) and it works quietly, so that you will be inclined to use it to whisk away harmful chemicals and particles.  In addition, inquire about any other gas appliances such as water heaters, clothes dryers and space heaters.  The inspector should note their age and condition (gas orifices can wear or rust over time, causing poor combustion) and if they are vented properly.  Here’s a good article for those who like to see what I’m talking about! 
• Outdoor sources of pollution.  Does it make sense to include the outdoors in an indoor air quality survey?  Yes–and here’s why.  No matter how tight your home’s envelope, we hope that there will be ample times of the year when the weather outside is just so gorgeous that it’s impossible to keep the windows closed.  At that moment, do you want to be worrying about what kind of air pollution could enter your home?  Although there’s little you can do about these sources, it’s good to know what they are and how often they may affect your ability to open windows, depending on the wind and weather conditions.  Here are just some of examples of outdoor air pollution: living near 
  • a busy thoroughfare or bus station
  • oil wells or refineries
  • trash dump
  • Stagnant farm pond or standing water (like used tire recycling center)
  • neighbors who burn trash or wood consistently
  • farms that crop dust or use aerosolized fertilizers
  • Areas that employ insecticide spray trucks
  • Golf courses and other public areas that use copious lawn treatments
  • Businesses that perform outdoor renovation work like sanding or spray painting
  • Seasonal issues like wildfires, tree pollen, ragweed, etc.
• New house smell.  New homes, just like new cars, can have many sources of VOCs, most dangerous and common among them being formaldehyde.  If you consider a newly finished or furnished home, find out if it has the following:
  • Press-board cabinets (most commonly found in kitchen, bathroom and garage)
  • Paneling 
  • An attached garage (see next point)
  • Whole-home air fresheners: terpenes in air fresheners can react with ozone to create formaldehyde (bustmold.com)
  • New drapery (International Association of Certified Home Inpectors)

Those were the biggest offenders, but new vinyl windows, insulation, drywall, caulks and adhesives can also off-gas VOCs.  This site gives detailed reviews on building products that “cure” quickly or are more tolerable for chemically-sensitive people.

• Attached Garage.  What?  Why is my attached garage a liability?  Attached garages are used for activities that people normally wouldn’t do in the home, AND they usually have air leaks that can infiltrate the home, since they are attached.  That’s why generators, motor vehicles and combustion-driven lawn equipment should never be allowed to “idle” or run continuously in the garage, even with the door open!  Also, although it may be the only sheltered place available to do home projects and hobbies, do realize that the fumes from paints and glues may work their way into the home through a leaky door, vents, and other unseen air passageways.  
• EMFs.  Although their effects are very controversial, electromagnetic fields (such as wi-fi, high-voltage power lines and stations outside and communications towers) can actually contribute to lower air quality in a home that is predisposed to mold issues.  If you have researched this topic and are concerned, you will want to know EMF sources in the neighborhood, as well the types of the wi-fi router and smart appliances, and where they are located.  Studies have found that mold growing in homes or buildings can actually be amplified by EMFs – causing mold to grow more rapidly and spread further. EMFs may also trigger the mold spores floating around in your house or body to release more mycotoxins. (jillcarnahan.com).  See our post ‘Taking our homes back from mold’ for more information.
• Wildlife.  Crazy as it sounds, if you live in an area with certain protected species, you may not be able to evict them without a special permit, or during certain times of the year.  For example, the Florida bonneted bat is a Federally endangered species that cannot be evicted from a home or building without a permit (floridabonnetedbat.org). Bat guano is extremely fragile and can become airborne if it is disturbed. Inhaling bat guano can spread Histoplasmosis, a major respiratory illness, and rabies to you and your family. (skedaddlewildlife.com ; this page also shows a short video of how bats can enter the home through the smallest of spaces!)  We at HypoAir were contacted by a homeowner who was not allowed to evict a family of bats during breeding season, and so sought air purification methods.  

Research on home air quality can help you avoid or mitigate unhealthy living spaces, make your home more comfortable, and even save money in many cases!  Make sure to check the date of any published materials on- or offline, because building codes and theories about air quality change (for example, some of the Building America recommendations made in 2005 have been superceded by newer technology).  Thoroughly inspecting and researching where you and your family will spend most of their time is worth it!