Monthly Archives: June 2022

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

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

If you go into a large building like a mall, warehouse or gymnasium and look up, usually you’ll see the ventilation system of ductwork running through the upper part of the room.  Even in many studio loft apartments, the ventilation system is exposed in the ceiling to give that “industrial” look.  I recently ran across a fabric ventilation distribution system, which are fabric “ducts” that disperse air in large rooms similar to the metal ones.  There are several differences in these fabric ducts, however. 

Dispersion vs. Distribution

I found this part very interesting, because I never really thought about the difference between these 2 words before.  “Dispersion” means “the action or process of distributing things or people over a wide area”, but “Distribution” means “the action of sharing something out among a number of recipients.”(Oxford Languages)  While the two definitions sound similar due to sharing something, Dispersion talks about area (infinite places) , while Distribution talks about recipients (finite things).  When you’re talking about ventilation and air, Dispersion in my estimation is preferable!  You can see the difference in this picture:


Air is entering from the right and traveling to the left.  On the metal system, you can see three vent terminals blowing out air.  The fresh air is concentrated at these points and after each, there is a lower pressure inside the vent tube, so the ductwork diameter must be decreased in order to keep velocity up, otherwise the last vent (on the left) will not put out air at the proper velocity to cause mixing in the space.  (Tor a great in-depth explanation of this, visit There are several problems with this:  if the ductwork is not sized correctly, the distribution will not be effective.  You know that room in your house that seems to always be significantly hotter or cooler than the thermostat setting?  The problem could be that the ductwork diameter is not sized correctly for your distribution system (the distance between the air handler and from vent to vent).  Modern residences use a lot of flexible ductwork instead of rigid metal ductwork, but the flexible acts the same as the rigid in that it has defined diameters and distribution points.  

In contrast, the fabric duct on the bottom has a series of tiny holes in a line.  I think this has a great resemblance to an old-fashioned garden soaker hose.  When a gardener wants to slowly water his whole garden, instead of just one point at the end of his hose, he can run a soaker hose up each row.  The soaker hose has a series of tiny holes that drip water at each point.  Similarly, this fabric duct really creates “dispersion” by releasing air along its entire length instead of just 3 vents.  You know the feeling of sitting under a vent or not sitting close enough to a vent?  You’re either too hot or too cold.  The dispersion system of the fabric duct better avoids cold and hot spots.  Apparently one of the first fabric duct systems were installed in a Danish slaughterhouse to address draft issues that were causing employee discomfort and sickness.  (

Fabric doesn’t sweat

The problem of condensation is a very familiar one in ventilation.  Wherever you have cold surfaces meeting warm, humid air, you’re going to have condensation, and this traditionally happens wherever metal ducts or vents are not insulated properly.  The very nature of fabric (the coefficient of thermal conductivity of fabric is much lower than that of galvanized steel ( allows it to be used uninsulated as a duct, because condensation is not an issue.  There are several benefits to the non-conductive quality of fabric:

  • No condensation = no water dripping on furniture or people!
  • No condensation = reduction in mold issues.
  • No metal and condensation = no rust problems.
  • The lack of insulation also gives greater efficiency in fabric ducts, because traditional metal ducts with interior insulation cause friction to the air passing through.  Traditional flex ducts have an internal spiral wire support, which also causes friction.  Fabric ducts can be supported externally by cable, tracks or hoops, eliminating sources of internal air friction from support. 
  • The lack of insulation also gives greater sanitation in fabric ducts, most of which are washable!  

Fabric doesn’t rattle

You’ve heard it before: somewhere in an old ventilation system, there’s a “screw loose” and the vibration of metal on metal is completely distracting!  Fabric in general can be much quieter and even reduce noise coming from the air handler through the installation of a fabric noise attenuator (  

So, for all these benefits, why aren’t fabric ducts becoming popular in homes?  It all comes down to design.  Fabric ducts work when they are placed inside of the space they serve, meaning they are visible.  The fabric duct can be the same color as the ceiling (camouflaged) or a contrasting color, but having ductwork inside the conditioned space necessitates higher ceilings (>8 ft) and an open floor plan works best, where it’s not required to penetrate walls to go into different rooms.  So, for large modern designs, why not consider fabric ductwork?  It’s even possible to print them in any design you can conceive–how about blue skies and clouds, tree branches, an abstract design or fun primary colors?  The ceiling’s the limit!

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

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. 

Ok, I won’t leave you floating here.  The real ways that submarines make oxygen are pure chemistry and physics: electrolysis of purified water, and burning chlorate candles (a very hot-burning cylindrical candle that actually puts out oxygen instead of consuming it!).  Submarines filter CO2 out of the atmosphere by using MEA (methylethylamine) to absorb it, or by using lithium hydroxide canisters to absorb it (lithium hydroxide canisters are also used by spacecraft like the Space Shuttle and International Space Station (

Photo by Taylor Vatem on Unsplash

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

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

  • 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 . Fire and smoke maps are available under the heading

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 (  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, 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. ( 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.  (  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, “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.”(  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. 
It’s not a matter of if, but when…according to a Wells Fargo survey in 2021, 84% of Americans live in areas that have experienced some form of natural disaster in the last three years, but not many are prepared for it. Be part of the ones who are prepared, because you never know how you can help your family and neighbors as well!

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

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 (  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. (
  • 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 (, 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.
    • 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 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 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

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.
  1. 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!  
  2. 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!  
  3. 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, 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.

  1. 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 (
  • 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. 
  1. 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. (
  • 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
  1. 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.
  1. 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:
  • 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 ( 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. 
  1. 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. (  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. (
  • 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.  (  
  • 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! 

Photo by Jason Jarrach on Unsplash

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

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:

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. (

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, 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:

  • 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!

Photo by Will Francis on Unsplash

How’s the air quality in your laundry room?

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, here are some of the other ways you can reduce fine particle pollution in your home and outdoors:

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:
  • Do not use screws to connect sections of ductwork together because the sharp end can catch lint inside the duct. (
  • 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!

*A 2011 study by Anne Steinemann, University of Washington professor, identified 25 VOCs in household dryer exhaust, including 2 potential carcinogens (acetaldehyde and benzene).

Photo by PlanetCare on Unsplash

Can I avoid mold with JUST ventilation?

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.


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: 

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 (  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.”(

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 (

Outside: 91 deg F, 54% humidity = 72 deg F dewpoint (

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!

Photo by yechan park on Unsplash

Power Outages and Air Quality

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. ( 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: (

  • 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

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 (  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)