Monthly Archives: June 2023

Summer Cooling: What are our options?

Many places in the US and around the world have broken temperature records this June.  Whether you’re in Minnesota or south Texas, it can be tough to keep your home cool during summer while maintaining a decent air quality.  We’ll go over some of the most popular ways of cooling your home and maybe some you haven’t thought of.  

If you’re not familiar with the different types of air conditioners and how they work, check out this article.  Note that newer air conditioners are also often “heat pumps” that can reverse the flow of refrigerant to provide heating in the winter.   

Central Air:  About 66% of homes in the US have central air conditioning, but this is not spread out evenly over the country.  As one would expect, central A/C is more prevalent in the south (37%), west (22%), and midwest (21%), versus the northeast (17%), and newer homes are more likely to have it.  (How Much Value Does Central Air Add to Your Home?) The best thing about central air conditioning is its distribution system, which allows multiple rooms to receive cooling and filtration from one unit.  With any air conditioning, it’s very important to do the following things:

• Keep your home closed (a sealed system) so that warm, moist air is not introduced.  Letting in humid air from the outside will quickly increase humidity inside, because air at a lower temperature cannot hold as much moisture as warmer air, and humidity climbs.  This applies to windows, doors, and any significant leaks (like the door to an unconditioned attic or crawlspace).   

• Change the filter on your unit regularly!   We can’t emphasize this enough: a dirty filter not only puts extra stress on the machinery like fans and compressors, but it increases cooling costs, and when the filter gets dirty enough, air will start to leak around the filter and get your evaporator coil dirty, providing food for mold.  Using the highest MERV possible for your unit will help keep the system clean and your air clean as well.  You can check out our article here to find out how to get more filtration out of your current AC system. 

• For extra filtration, you can cut filter material to fit your vents, just don’t forget to clean or change these regularly, too. 

• Get your unit serviced regularly.  Here are some things that the HVAC tech will do for you during a service visit:  inspect the inside coils, clean the outside coils and straighten fins if necessary, check the refrigerant levels and add refrigerant if necessary, and test the thermostat.  An HVAC system is a big investment (average $7000), so you’ll want to take care of it!  

• Make sure your insulation is up-to-par: check air ducts to make sure they are not crimped and are fully insulated, and make sure there are no “bare spots” in the home’s conditioned-space envelope (ceiling or roof).  You’ve got to keep that cool air where it belongs!

Mini-Splits have most of the same parts as a central system, but they don’t have ducts to distribute cool air.  Instead, you could have one outdoor unit combined with up to eight indoor units, with the outdoor unit distributing refrigerant, not air.  In this way, you’ll have eight separate fans and filters inside, but these are smaller.  Mini-splits also have filters, so you’ll want to clean or change these on a regular basis.  One disadvantage with mini-splits is that the air filters tend to be similar to window air conditioners, which are cleanable, but they don’t provide high filtration, just large dust capture.  You will also want to get your units serviced regularly by an HVAC technician.  To get additional dust filtration, try adding standalone HEPA filters in the rooms that seem to get the most dust. 

Window Air Conditioners have come a long way in efficiency and looks!  They are one of the quickest installations, too: from buying one in your local home improvement store to having cool air in your space, could take as little as 1 hour.  Window air conditioners are a sort of “plug and play” cooling solution, but they also require regular maintenance of cleaning the filter.  Because the filter is equivalent to a very low MERV, like mini-splits, you’ll want to add a standalone HEPA filter to reduce pollen and dust.  In addition, if your window unit is more than several years old, it would benefit from a deep cleaning (see our article for tips on how to do that).   Some window air conditioners also have a feature that mini-splits and basic central systems don’t: a fresh air vent.  When this vent is open, you can get a small stream of fresh air from the outside, to dilute stale indoor air.  The only problem is that this air is usually not filtered or conditioned:  it’s the same as “cracking the window” without a screen.  To find this feature and operate it correctly, sometimes you’ll need to refer to the owner’s manual.   New window units with “inverter” type motors can be extremely efficient and this “saddle” style unit by Soleus even gives you your window view back, because it hangs below the window on each side.  It also has a dehumidifier setting to lower the humidity in your space. 

Portable Air Conditioners have become popular because like the name suggests, they are the most portable.  They can cool spaces without a window, as long as you have a place nearby to send the heat through the exhaust duct (through a sliding door with an adapter kit, for example).  You will also need a drain to collect condensate, or you will need to empty the reservoir every so often.  Portable air conditioners have the minimal filters similar to window air conditioners and mini-splits, so they are not able to filter smaller particulates.  It’s really important to clean these filters on a regular basis to keep your air conditioner working well!  Another downside to portable air conditioners is that they are less efficient than window air conditioners, and they have bulky hoses that aren’t the most attractive.  

Fans are the most common cooling systems we have, and many are cheap, at less than $50.  Fans cause evaporative cooling, where the circulated air carries heat away from our bodies in the form of water vapor.  Fans work well to cool us down if there is some humidity in the air.  (See our article about the detrimental effect of fans in extreme dry heat.)  You can use a combination of ceiling fans and portable fans to move air from cooler to warmer areas of your home.  Dreo Air Circulators are very powerful, efficient, and quiet because of the fan design, and because they use brushless DC motors that have a large range of speed with low energy consumption.  Since most fans don’t have filters, you can add standalone HEPA filters to cut down on dust, or add cloth filters to your tower fans. Filters for box fans (20x20”) are mainly the replaceable type, not cleanable, but $45 for a 4-pack of MERV-13 filters could help your space stay a lot less dusty.

Opening the windows is an option if you live outside of polluted urban areas, wildfire smoke, or excessive heat and humidity.  In these cases, it’s best to leave the windows closed and curtains drawn to preserve coolness as long as possible in the day.  If inside temperatures start to equalize with outdoors, however, you can use regular window screens in pristine areas, and Window Ventilation Filters in more polluted areas.  Although the filters restrict airflow slightly, they provide a good buffer against dust and pollen.  Here again, standalone HEPA filters will also help reduce dust in your home. 

Evaporative coolers, also known as Swamp Coolers, began to be popular in the 1920’s and 30’s when electricity was available, but residential air conditioning was not affordable/accessible. (Window air conditioners were invented in 1931 and central air conditioning was offered in 1931 but many Americans could not purchase them due to the Depression).   Swamp coolers use a fan to blow air over a wet membrane, which, if not cleaned regularly, begins to grow algae and smell like a swamp!  This older type of membrane is definitely not something we would recommend for air quality, but newer models like those made by Big Ass Fans uses a proprietary resin coating on the media that resists the growth of algae and mold to keep your airflow clean and people healthy.  Following the cleaning and maintenance guidelines are very important, too.  Another downside of this type of cooling is the massive airflow that could kick up a lot of dust.  However, if you have a large outdoor or unconditioned space and adding humidity into the air is not a problem, then an evaporative cooler could help you stay cool.  It would even help to cool a porch, from which you can open up air to your home to take in cooler air.

Heat Pump Water Heaters can actually cool your space.  It sounds counterintuitive–til you consider what this machine is actually doing.  Instead of creating heat by an electric coil or gas furnace, this type of water heater pulls heat from the surrounding air–in effect making the room in which it’s installed, cooler!  If you have the water heater installed in the garage or another unconditioned space, you can still reap the benefits by using ducts to bring warm air from your house to the heat pump, and cool air from the heat pump back to your house.  Heat pump water heaters do cost more than the basic electric or gas varieties, but according to the Department of Energy, they can be two to three times more efficient than a regular electric water heater.  However, when you consider you’re getting free cooling during the summer, you can deduct this cost from your cooling bill.  Another consideration is the size of room where it is installed.  It must be installed in a room at least 12’x12’, or have ducting to access larger areas, so it can pull the heat it needs from the ambient air.   If it’s time to replace your water heater, check with your plumber to see if a heat pump water heater would work for you!

There are many ways to move cool air from the basement into your home, but consider the quality of basement air before you make this move.  If it’s musty or moldy smelling, you’ll definitely want to get rid of that mold before trying to move that air upstairs.  For this reason, we can’t recommend circulating basement air in the rest of your home.

Whichever way you decide to cool your home, make sure that air quality doesn’t suffer.  Our Germ Defenders, Mobile Air Angels and Whole Home Ionizers sanitize air using bipolar ionization, killing microbes and agglomerating dust and pollen so it’s easy to filter or clean.   Extreme heat tends to lead to increased air pollution, so be conscious of air quality when you open the windows, or even when they are closed and outdoor air seeps in (as it always does except in the tightest of homes).   Check out our article to find out how to ride out a heat/air pollution wave safely!

Should I move out of my home during mold remediation?

We get this question a lot from homeowners who have discovered mold in their homes and need professional remediation to remove it.  Should I try to stay while the mold is removed and my house is put back together, or find another temporary home?

There are several considerations in making this decision, and they’re not easy.  Sadly, mold remediation is not “elective” or optional once you find it and discover the extent of mold damage.  The traditional option of renovating “room-by-room” is not available here because if it has mold, it has to be remediated as soon as possible if you want to live in your home!  

Why should I move out during remediation?

First off, If you’re not used to putting yourself first, you need to consider the value of your health.  Staying in your home while mold is removed and materials are replaced simply may not be safe for certain individuals.  The following are just some of the conditions that make it safer to leave:

• Anyone diagnosed with Chronic Inflammatory Response Syndrome (CIRS) or Mast Cell Syndrome (MCS)

• A compromised respiratory system or respiratory illness like asthma, COPD, emphysema, cystic fibrosis or any number of similar conditions.  Why?  Small particles and mold released into the air can directly affect your lungs and can be extremely dangerous for immuno-compromised individuals.

• Heart conditions like arrhythmia, congestive heart failure, unstable angina, and any number of similar conditions.  Why?  Small particles and mold released into the air can directly affect your heart when they pass through your lungs into your bloodstream and can be extremely dangerous for immuno-compromised individuals.

• Mobility handicapped people and the elderly may find it difficult to perform more cleaning and move around areas under construction

• Work-from-home employees:  construction noise can be distracting and unproductive

• Families with young children and/or pets  Even with protective barriers between you and the construction, you may find that your living space has increased dust on all surfaces, danger of children and/or pets getting into construction zones,  and construction noise from 7am on any time during the workday.

Secondly, most remediators will say that moving out is the best option to minimize time and labor.  According to Anna Williams, founder of Your Beautiful Home, there are multiple reasons.  If you live at home during the work, the construction crew will have to take extra care to clean up each evening before leaving, as well as pack up their tools.  This takes at least 30 minutes in the evening, plus time in the morning to unpack tools. (Move out during renovation or live through it? That is the question!)  Also, they may not have the easiest access if you are living there, for instance walking and carting tools to the back door to avoid your living space.  So, making it easier and quicker on the remediators means less time and money spent.

And of course, if the remediation requires extensive gutting to your home, it may be just too inconvenient to try to live there.

If you decide to leave, family and friends usually have the cheapest “rates” of any accommodations, but will your relationship survive the remediation?  If your contractor has a reputation for completing projects on-time, staying with family may be a good option.  Alternatives include:

• Vacation rentals like Airbnb and VRBO

• Extended stay suites

• Sublets

• Corporate housing/short-term rentals (contact a corporate housing agency)

If you move out, you’ll want to make sure to do the following:

• Store food items in airtight bins

• Discuss power requirements and when the power will be cut off (will it affect your freezer/any other climatization?

• Place plastic dust covers on furniture, clothing and carpets if possible

• Secure any areas of the home that contractors don’t need to access, take or lock up valuables

• Notify your home insurance and security company

• Check the “containment” that the contractor has set up.  Be sure to discuss your HVAC system, which can broadcast mold and dust throughout your home if it’s not secured!  If temporary ventilation is needed during extreme heat or cold, the contractor should be able to provide it.  

• Plan for extra weeks or months in case the remediation schedule doesn’t proceed as planned.

Why should I stay?

Finding alternate accommodations can be stressful if you have to stay with others, or expensive if you have to pay for a rental for your family.  For these reasons, many decide to stay at home.  Homeowners who decide to try to live in their home during remediation should know about the stresses they may endure!  It’s not easy to have workers coming and going through your personal space.  Here are just a few considerations:

• Increased dust throughout the home

• Increased noise during workdays

• Temporary (or prolonged) power and water disruptions

• Ventilation during extreme temperatures

• Child safety

• Parking issues–will there be many vehicles and/or a dumpster parked in front of your house?

• Access to your kitchen

• Access to at least one bathroom and shower or tub

• Access to laundry facilities

• Sufficient clean space for your family to sleep

• Sufficient space to work if working from home

• Delays to the schedule may make the remediation longer than expected

It’s a lot to consider.  Of course, make sure you have as many options available as possible before deciding, including knowing if your insurance will pick up any of the cost for relocation.  If not, you can check with local, state and federal agencies for assistance.  

Staying at home during a mold remediation carries an extra risk: airborne mold.  For this reason, we recommend purchasing extra HEPA filters to place around your living area and portable air sanitizers like the Air Angel and Germ Defender.  Containment of dust and mold spores has to be top-notch–make sure that the contractor follows all safety standards for containment!

Working with the contractor on setting a budget and timeline should be a top priority.  Many contractors may think that delays are acceptable if the homeowner is living in the home or with family–after all, you won’t be paying rent–but make sure that this is not their mindset by including deadlines in the contract, and penalties or cost reductions if they are not met.

By all means, ask for help whenever you can.  Whether it’s taking a weekend getaway break, taking vacation during the remediation, asking for help with children and pets, or having dinner with friends more often, you’ll need to pace yourself so that your health and your relationships aren’t “gutted” either!  

BALOs: voracious good bacteria

Bacteria in general have bad connotations: infection and illness to name a few.  But increasing awareness about the benefits of probiotics and natural gut bacteria have taught us that not all bacteria are bad: there are good bacteria too.  Bdellovibrio is in the good bacteria category and recent discoveries about it are spurring more possible uses.

Bdellovibrio bacteriovorus, which was first discovered in 1962, is a gram-negative, aerobic bacteria, which means it has a hard, outer shell that resists the purple stain used to differentiate strains of bacteria.  (For more information on gram negative and gram positive bacteria, check out our post here.)

Bdellovibrio is also a predator.  It is capable of killing and replicating inside over 100 different types of Gram-negative bacteria, including antibiotic-resistant pathogens, giving it a reputation of being a “living antibiotic”.  These prey bacteria include such well-known pathogens as Escherichia coli, Helicobacter pylori, Klebsiella pneumoniae, Pseudomonas, and Salmonella.  This predation behavior has even spawned a new acronym for this type of bacteria: Bdellovibrio and Like Organisms, or BALOs.

According to the following analysis, Bdellovibrio sounds like a voracious alien by attaching to, penetrating, and killing host bacteria, then using them to incubate its own progeny:  “In the wild, B. bacteriovorus uses chemotaxis and a single polar flagellum to hunt groups of prey bacteria. Once in close proximity, B. bacteriovorus collides with individual prey and attaches through an unknown mechanism. Next, B. bacteriovorus invades the prey periplasm (layers around the cell), likely through use of retractable pili, and secretes hydrolytic enzymes that kill the prey within 10 to 20 min of invasion. The predator subsequently remodels host peptidoglycan to form the spherical bdelloplast, where it degrades intracellular contents to fuel its own filamentous growth (liquidates the insides of the prey to fuel replication). Finally, 3 to 4 h following initial contact, the prey cell is lysed (ruptured), and four to six daughter cells emerge from their protected niche (the bdellovibrio babies emerge). Wow!   

Bdellovibrio is found naturally in soil and water, including rivers, lakes, the open ocean, and sewage and wastewater treatment plants (WWTPs).  They are also found in the gills of certain aquatic animals like crabs and oysters, and some mammal intestines.  

Here are some of the proposed uses of BALOs:

• It could be used in a probiotic to foster healthy human gut microbiota (Higher Prevalence and Abundance of Bdellovibrio bacteriovorus in the Human Gut of Healthy Subjects)

• It could be an effective treatment for pneumonia in lungs, as both B. bacteriovorus and M. aeruginosavorus could reduce the burden of K. pneumoniae in rat lungs, and B. bacteriovorus treatment is also effective in Yersinia pestis infection of mouse lungs. However, it was found that B. bacteriovorus and M. aeruginosavorus did not reduce pathogenic colonies in the blood, as it did in the lungs of these animals.  (Predatory Bacteria Attenuate Klebsiella pneumoniae Burden in Rat Lungs, Susceptibility of Virulent Yersinia pestis Bacteria to Predator Bacteria in the Lungs of Mice)

• It could be an effective treatment for Cystic Fibrosis (CF), in which patients have a defective gene that hampers immune response and causes them to be prone to chronic lung infections with an exaggerated inflammatory response.  In CF patients, instead of a diversity of microbiota, only two pathogenic microbes prevail, namely usually the Gram-negative P. aeruginosa and the Gram-positive S. aureus.  Therefore Bdellovibrio was used in a 2014 study to “challenge” these 2 strains in a lab setting, and it was able to reduce the biofilm of both cultures dramatically, even in “flow” settings.  The scientists were even able to photograph (at 30-50 times magnification) Bdellovibrio preying on S. aureus bacteria (see photo below).

Source: Study: Bdellovibrio bacteriovorus directly attacks Pseudomonas aeruginosa and Staphylococcus aureus Cystic fibrosis isolates

• Prolong food storage:  This study proposes that Bdellovibrio could be used to prolong the shelf life and reduce additives to packaged meat, because it was tested on chicken slices and canned beef and found to reduce colonies of E.Coli by 4.3 log and 2.1 log respectively.  The Bdellovibrio was able to lyse (rupture) all the strains of E. Coli that were tested.  In a separate investigation of Bdellovibrio and E. Coli, this video shows how an actual Bdellovibrio cell multiplies inside an E.Coli cell and destroys it from the inside out.

• It’s already been recognized as a mode of controlling bacteria in water supply systems.  In 2020 in Varberg, Sweden, a municipal water supply company decided to replace its chlorination system with ultrafiltration, which is an ultrafine mesh filter that prevents microbes from passing through.  Scientists monitored the results closely following discontinuation of chlorine, and some bacteria grew, but then decreased drastically.  By the third month, Bdellovibrio had flourished and harmful bacteria had diminished.  This showed that chlorine had actually suppressed the natural predatory action of bdellovibrio in the biofilm on the inside of drinking water distribution pipes where the good and bad bacteria live. (Predatory bacteria could be used to purify water in the future, study suggests)

So, what’s keeping us from using BALOS as natural antibiotics?  Of course, scientists want to make sure that there will be no harm to humans.  A number of studies using the two BALOs B. bacteriovorus and M. aeruginosavorus “demonstrate their inability to invade mammalian cells, and no apparent pathological effects or signs of cytotoxicity or reduction in cell viability, supporting the proposition that these two BALOs are inherently non-pathogenic to mammals.” (Biotechnological Potential of Bdellovibrio and Like Organisms and Their Secreted Enzymes)  However, scientists are also concerned that prey bacteria could become resistant to it, if it incompletely eradicates the prey. 

In addition, varying amounts of oxygen are necessary for BALOs to work on their prey.  Finally, in complex microbial environments like in our bodies or even in a wastewater treatment plant, it’s not always easy to predict how introduced BALOs will change the biome or which microbes they will prey on, although some do have preferred prey.  Certain chemicals also reduce their effectiveness.

In conclusion, it’s amazing what goes on all around us in microscopic realms.  BALOs could be harnessed in many different ways to improve our health: just the Swedish experiment of removing chlorine showed that it’s not always necessary to use harmful chemicals to kill bad microbes.  Although a lot more research needs to be done, it’s good to know that there are bacteria out there that are on our side! 

How a moth’s wings could make your home quieter

Noise is an important part of our home environment.  The most beautiful, well-designed home, if situated next to a busy, noisy road, falls in value due to its location, location, location.   Apartments in the city may have beautiful balconies that are never used because of the drone of traffic all around.  What if nature offered an innovative sound-absorbing “cloak” for your home?

Bats use echolocation to find their prey.  Smooth surfaces that lack scales or fur make the echoes louder, allowing the bat to close in quickly.  Animals with fur or scales, however, can elude the bat more often.  Scientists have discovered that a certain type of moth have scales that overlap in unique ways to provide exceptional sound-dampening. 

Diamond Light Source is a synchrotron in the UK (a synchrotron is a circular particle accelerator), which was used to examine the nanosized scales on the wings.  According to Professor Christoph Rau, a scientist at this synchrotron, the sound absorbing properties of thoracic moth scales are capable of absorbing about two thirds of the sound energy emitted by their predator, the bat, and significantly increases the insect's survivability.

A separate study by the University of Bristol's School of Biological Sciences showed that the wings absorb as much as 87% of the incoming sound energy. The effect is also broadband and omnidirectional, covering a wide range of frequencies and sound incident angles.

"What is even more impressive is that the wings are doing this whilst being incredibly thin, with the scale layer being only 1/50th of the thickness of the wavelength of the sound that they are absorbing," explained lead author Dr. Thomas Neil.

What could we do with such incredible sound-absorbing performance?  Certain types of noise, like car horns and screeching tires can be detrimental to our health, as we detailed in this article.  Then, there’s also the noise pollution that comes from neighbors or even your own home, which can affect your sleep or concentration while studying or working from home.    Wallpaper or ultra thin sound absorbing panels would vastly improve interiors or exteriors in cities and other loud locations.  Office walls and places where highly sensitive information is discussed could use it.  Even libraries, children’s nurseries and our own bedrooms could use it.  Can you get too much quiet in a space?  I don’t think so, when the world’s noise is only a few steps away!

Tackling Dust in Your Home

Dust is one of those things that never completely goes away, like mold, but keeping both at a minimum in your home is key!  There are a lot of weather conditions that increase dust, but in general, heat and low humidity are two of them.  When these occur, you’ll not only see an increase of dust in your home, you’ll be breathing more of it because the less humidity, the longer particles stay afloat.  Yuck!  Getting it under control takes some effort, but we’d like to help!

Invest in the right tools

We see deep discounts all the time on home appliances that look like they make our lives easier–but they end up to be a waste of money.   This is where it pays to research–and only buy what will do the job, not the gadget with the most features.  The tools we’re going to talk about are very important to your family’s health, so we hope that you keep these requirements in mind and buy wisely! 

1. Air Cleaner

With dust in the air, you can do all the cleaning you want and then–BOOM–the dust continues to fall out of the air after you stop cleaning, not to mention all the dust you are filtering with your nose and lungs!  If you live in a dusty area, an air cleaner that uses HEPA filters is imperative.  

For value and solid performance, Medify Air has a range of air purifiers that is hard to beat.  You can find one for every size room in your home, from small nurseries to “great” rooms, with simple controls and most with filters that can be vacuumed gently once a month on the pre-filter side to extend their life.  They use True HEPA H13 filters, which in general last 3 to 6 months.  

Another great option is the CoWay AirMega Mighty, which has been highly rated for a number of years by the NY Times Wirecutter review for dusty rooms up to 250 square feet.  Their testing has used the same filter for up to a year with good performance (however of course you’ll want to have new filters on hand just in case you are caught in an exceptionally-poor air quality day).  

2. Dusting, Vacuuming, and Mopping

I wish I could tell you differently, but these chores are a must.  If you invest in the right tool(s), however, you can enjoy your clean surfaces with less work!  Dusting should be done with a dry microfiber cloth (check out this video to learn how to dust properly–yes there are techniques that are more effective with less work!)  Then, get both vacuuming and mopping done at the same time with this ONE TOOL (I’ve touted it in other articles, but here it is again): with the CrossWave floor and area rug cleaner by Bissell ($257).  It leaves your floor cleaner than if you had vacuumed and mopped separately!  It has a rug cleaning function, and it has a HEPA filter included, so no dust is escaping your machine and going back into the air.   For people who have mobility or strength issues, this machine absolutely reduces the straining scrubbing actions that normal mopping requires, and it also comes in a cordless option.  If you check local discount stores, there are many reconditioned models that sell for less than half this price (I got my corded one at Ollie’s).  In addition, of course the manufacturer wants you to use their patented floor cleaner, and states that using any other cleaner will violate the warranty.  Unfortunately, Bissell products mostly rate an “D” grade from the Environmental Working Group for toxicity to humans and the environment, but if you do decide to substitute a non-toxic cleaner, we have just the one for you: a recipe using TotalClean.  TotalClean has no fragrance and no toxicity, you can clean your floors as often as you want without adding more VOCs and chemicals to your home.  Here’s the full recipe for a Bissell-like non-toxic floor cleaner:

Machine Floor Cleaner Concentrate Recipe (this is the concentrated cleaner so you add it in replace of the manufacturer’s cleaner, with the recommended amount of water, adapted from this very informative article):

• 1-¾  cups TotalClean Concentrate
• ⅛ cup rubbing alcohol
• ⅛ tsp dish soap
• 5-10 drops essential oil (optional)

If you simply must have a separate vacuum and mop, though, make sure the vacuum uses certified true (make sure the label says “true”) HEPA filters with an airtight, sealed filtration system.  You don’t want that dust to be recycled right back into the air!  As for mops, The Maker’s Mop is an ingenious tool for dry and wet-mopping, dusting, and cleaning up after huge spills.  And, being “cordless”, I guess it’s handy to have around in the case of a power outage!  (20 Tips To Prevent And Reduce Dust In Your Home)  

3. Fresh-air ventilation WITH filtration

If your rooms are stuffy (too much CO2!) and you don’t have central air conditioning, make sure you only open windows with filters in them!  That’s right, screens may prevent mosquitoes and flies from coming in, but they do nothing to filter dust.  Our Window Ventilation Filters are adjustable so that you can still open your windows for fresh air and block out most of the dust. 

If you like to open your windows wide for fresh air often, you should consider replacing the fitted window screens with nanoscreening.  Nanoscreening does cut visibility through the screen somewhat compared to normal insect screens, but many customers like the additional privacy it offers.  AllergyGuard nanoscreen offers a kit that is super-easy to install with double-sided tape.   If you re-screen a few windows with this kit and like how it performs, you can go to their website for a larger roll and video on how to install it with spline, the skinny rubber tubing that is normally used to keep screens in place.  

4. Change your HVAC filter more frequently.  

If you have a hard time remembering to do this, just enroll in an auto-ship subscription to make it easy to have them available when you need them.  If you’re concerned about changing it too frequently, check out our tips for getting that interval just right.

5. Don’t carry the dust in with you!

We’ve written a lot about this practice, which ranges from taking your shoes off at the door and using a doormat, to doing your best to clean dusty pets off before they come inside (umm, can we teach them how to brush themselves?)

6. Minimize.

This says so much in one word.  Minimize the fluffy pillows, fuzzy throws, carpeted flooring (don’t rip out carpet if you’re renting, though, obviously), knick-knacks and tchotchkes, piles of clothing, anything that you can do without, that catches loads of dust (children not included)!   If you want to have area rugs or carpet, consider changing them to wool carpets.  According to a 2015 study, wool carpets significantly improve indoor air quality by rapidly absorbing the common pollutants formaldehyde, sulphur dioxide and nitrogen oxides, known as volatile organic compounds, or VOCs, which are released from many common household items such as cleaners and disinfectants, air fresheners, printers and home furnishings.  A high level of formaldehyde (300 parts per million) was reduced to virtually zero in four hours, and nitrogen oxides from 300 to 5 parts per million in 24 hours, whereas nylon carpets did not perform as well.  The wool carpets retained the formaldehyde and did not remit them into the atmosphere.  When you choose a carpet, low pile heights are favorable so that dust and debris is easier for the vacuum to remove (with your True HEPA vacuum, of course!).    

How can I apply Altitude Simulation to my home?

Visitors and full-time residents in high-altitude locations are susceptible to altitude sickness, also called Mountain Sickness.  This is due to the lower atmospheric pressure and consequently lower oxygen molecules by volume, found in the mountains.  These illnesses include problems sleeping, fatigue, headaches, and even life-threatening pulmonary edema (buildup of fluids in the lungs).  At just 6,000 feet many people experience trouble sleeping, and, according to the Cleveland Clinic, about half of people who ascend to 8,000 feet will experience some form of altitude symptoms, and almost 75 percent of people will have effects at 10,000 feet. (Oxygenation for Mountain Hotels and Resorts)  Even one of the premier experts on altitude sickness, Dr. Peter Hackett, had a close call with pulmonary edema while mountaineering (video). Technically, even people at sea level can get “hypoxia” (the condition of low oxygen content in tissues) if the atmosphere is low in oxygen or their breathing function is impaired.  

Studies have shown that supplementing oxygen during sleeping reduces the effects of altitude sickness or hypoxia, while also improving daytime oxygen saturation and ability to function during the day.

Altitude Control Technologies (ACT) works with ordinary homeowners, as well as the US Air Force, US Navy, universities, professional sports teams, Olympic training facilities, etc. to provide “altitude simulation” for enhanced health and performance.  It’s a unique technology that raises oxygen levels in a room to “simulate” lower altitudes.  In homes, ACT only services bedrooms because with 8 hours of sleep at a simulated lower altitude, people can become better acclimatized to their physical altitude during the rest of the day.  This informative video shows the machines, how they work, where they are installed and how they are controlled.

ACT machines take in air from outside, splits up oxygen and nitrogen, sends the nitrogen out of the house, and the oxygen to the bedroom(s).  For example in Colorado, oxygen levels are increased by about 30% to simulate an altitude closer to sea level.  The control sensors monitor the oxygen saturation, barometric pressure and CO2 in the room constantly.   In this way, too much oxygen (which violates the National Fire Protection Code) is never a problem.  

The oxygen machines installed by ACT use molecular sieves.  They are placed outside the bedroom(s) in the attic, mechanical space or crawlspace so that noise and heat created by the machines does not impact the restful area of the bedroom.  To counter the heat of the machines that could otherwise place an additional burden on the HVAC system, ACT has developed an Alticool™ system uses a combination of fresh mountain air and exhaust fans to cool the machinery space.

Although the machines used by ACT are proprietary, many of the machines used by oxygen medical supply companies use Pressure Swing Adsorption (PSA) systems to separate oxygen from nitrogen.  Two pressure vessels are filled with Carbon Molecular Sieves (CMS).  In the first pressure vessel, clean compressed air is introduced, where the nitrogen and carbon dioxide is attracted to the CMS and oxygen is allowed to pass through.  The second pressure vessel is regenerated to “purge” the nitrogen and carbon dioxide from the CMS by vacuum and a small stream of pure oxygen.  Then, the vessels switch placement in the process and the first vessel is regenerated while the second vessel produces oxygen. (How Oxygen PSA Generators Work)

Because air pressure is lower at higher altitude, simulating a lower altitude in a room involves adding oxygen, which also increases air pressure in the room.  In building science, this is a “positive pressure” scenario, where good air sealing must accompany the installation so that the newly added oxygen doesn’t leak out of the room and cancel the work of the equipment!   For this reason, detailed engineering of the space(s) to be oxygenated precedes any installation.  The engineers take into account the room boundaries including doors, windows, walls and ventilation systems that are shared with other spaces, often specifying dampers that are activated when the system is in use.  New construction and pre-existing structures are candidates for the system, however it’s always less costly and easier to plan for such a system before the home is under construction. 

So you may be saying, how does all this apply to my home at sea level?  Even if you don’t live at or visit high altitudes, you can apply some of the principles of this technology to make your bedroom the optimal place for your body to recharge and repair itself while you sleep.  Let’s recap to understand how this applies to your bedroom:

• Getting a better sleep at night increases performance and cognitive facilities during the day. 

• Air-seal the room boundaries from pollutants by using air-sealing techniques at the door(s), window(s), corners, outlets and openings like can lights and ceiling fans.

• If you want more fresh, clean air, you can consider the following: 

• Use a window ventilation filter where you can open the window comfortably without excess humidity, heat or cold.

• If you have central air conditioning, you could switch the bedroom to a dedicated mini-split with its own filter and option to intake fresh air from outside, OR

• Add a fresh-air intake in your HVAC system and add an inline duct fan and filter to the vents serving your bedroom (here’s an inline duct filter). 

• Add plants that are low-maintenance and produce the most oxygen while filtering pollutants. 

• Check with your doctor to see if you suffer from sleep apnea or hypoxia.  Usually these are diagnosed through a sleep study.  If you are a relatively stationary sleeper, you could add oxygen to your sleep routine with a portable oxygen concentrator and mask or cannula.  Continuous positive airway pressure machines (CPAPs) are popularly prescribed but they do not increase the oxygen content of the incoming air;  CPAPs just increase air pressure slightly to keep breathing airways open while you sleep.

• Consider that outside noise can also reduce your sleep quality, so check out our recommendations to seal out unwanted noise, as well. 

• Make it a priority to clean surfaces and change your sheets at least once a week.  To help combat dust and allergens between cleanings, add an Air Angel and a standalone HEPA filter.  A dustmite-proof mattress encasement also helps to transform your bed from being a dustmite haven to a clean “nest”!

Consider what and how you are breathing during the most important time of the day–your sleep–and you may find that making small changes can improve your daytime enjoyment immensely!

Knock out the NOx

This title may sound like an ad for high-octane gasoline, but I’m talking about air pollution here!  In air purification “PM” or particulate matter often steals the show and drives the decisions behind purchasing this filter versus that filter and this purifier over that one.  But what about the gasses in air pollution?  Gasses are not particulates–they are harmful molecules in the air that cannot be filtered out by plain HEPA filters.  So what are they and how can we get rid of them?

NOx is one term for two nitrogen gasses commonly found in urban areas.  It includes nitric oxide (NO), which is a colorless, odorless gas, and nitrogen dioxide (NO2), which is a reddish-brown gas with a pungent odor.  They are produced during combustion: in factories, in transportation vehicles, and even boilers for heating apartments, office buildings, hospitals, universities, etc.  They’re also produced indoors by gas stoves and furnaces when they are not properly vented. 

Nitric oxide in ambient conditions is not harmful, as it dilates (relaxes) blood vessels and improves oxygenation.  However in higher concentrations, it does two things: it will create a burning sensation in your throat and chest as it changes into nitric and nitrous acid, and it goes deep into your lungs to react with blood cells and eventually be excreted by the kidneys.   Nitric oxide in the air that is not breathed in is converted to NO2, the other dangerous nitrogen gas, or precipitated in moisture as acid rain.  (Poison Facts: Low Chemicals: Nitric Oxide)  

According to Clarity.io, a manufacturer of air monitoring sensors, nitrogen dioxide pollution stays mostly concentrated in the area where it is emitted, meaning that areas with high vehicle traffic like urban areas tend to have the highest NO2 levels. (Clean air cities: Innovative approaches to improving air quality in urban settings)  NO2 is a pretty nasty gas: it causes inflammation of the respiratory pathways, worsened cough and wheezing, reduced lung function, increased asthma attacks and is likely to be a cause of asthma in children. (Nitrogen Dioxide)  

If you’ve been reading our articles or have any experience with air pollution or wildfire smoke, you’ll know that outside pollution eventually makes it into our homes, because they’re leaky.  Thus, we don’t have a “safe place” to get away from air pollution unless we leave the city or take steps to make our home air cleaner.  As we already discussed, just buying a plain HEPA filter or making a DIY air filter (Corsi-Rosenthal box) will not take NOx out of your home.  There are ways to get rid of NOx, however: upgrade to a HEPA filter with activated carbon, AND eliminate the sources of NOx inside your home.

A 2014 study conducted in Baltimore, MD found that a two-pronged approach really helped reduce the NO2 in homes:  

1. Replacement of unvented gas stoves with electric stoves reduced NO2 concentrations by 51% and 42% in the kitchen and bedroom, respectively, indicating that stove replacement impacts NO2 concentrations beyond the kitchen (even when the home also has a gas furnace or drier).

2. Placement of air purifiers with HEPA and carbon filters in the home results in a nearly 27% decrease in median kitchen NO2 concentrations immediately (1 week after placement), and reductions were maintained at 3 months following intervention. 

Although the study also included the addition of a ventilation hood in some homes, it was unclear whether the hood helped lower NO2 emissions (ventilation does help remove air pollution, but it depends on strict use of the hood during and after cooking).  

Activated carbon adsorbs the NO2 and secures it in the filter, until the filter is changed.  Adsorption of NO2 can be enhanced by 38-55% by adding coatings to the activated carbon, such as potassium hydroxide (KOH).  (Development of an activated carbon filter to remove NO2 and HONO in indoor air)  Even wildfire smoke has NO2 in it; according to this Canadian government environmental webpage, wildfire smoke is a complex mixture of gases, particles and water vapour that contains pollutants such as: sulphur dioxide, nitrogen dioxide, carbon monoxide, volatile organic compounds, fine particulate matter (PM2.5), and ozone.  Activated carbon can handle these gasses and VOCs, while HEPA filtration is used against PM2.5

Therefore, city dwellers, take note!  Whether it’s “business as usual” as pollution from downtown traffic penetrates your home, or wildfires hundreds of miles away turn the skies orange and hazy, a purifier with HEPA and activated carbon is your best bet to knock out the NOx.  Be on the lookout for purifier giveaways, too!   Here are some programs being offered at this time:

• San Joaquin Valley Air Pollution Control District (California) is giving away air purifiers to keep residents safe from air pollution.  If you live in the area, you can apply for one here. 

• The City of Philadelphia is giving air purifiers to early-childhood education centers and schools.  You can learn more and link to an interest form in this article.

• Project N95, a national non-profit working to protect people and their communities during the COVID-19 pandemic and beyond, has begun a donation pilot program of air purifiers for schools and other organizations.  You can fill out their form here.

Keep your eyes and browser open, as other organizations may spontaneously donate during events like the Canadian wildfires (the University of Connecticut gave away 100 DIY purifiers on June 8, 2023).  During such a time, it’s the neighborly thing to do!

The purifying power of sunlight

“Letting the sunshine in” has several purifying benefits–and sunshine is free!  Ultraviolet (UV) radiation has a higher frequency than visible light (you can’t see it), but it kills microbes.  UV radiation has three wavelength zones: UV-A, UV-B, and UV-C, and it is this last region, the shortwave UV-C, that has germicidal properties for disinfection.  the optimum range for UV energy absorption by nucleic acids is about 240-280 nanometers (nm); at this wavelength the UV breaks bonds in the nucleic acids of microorganisms, killing them.  Artificial UV lamps for germicidal use tend to emit energy around the middle of this range, at 260 nm.  (UV Disinfection)  If you want to know more about the sanitizing power of UV light, check out our first article here.  Here are some ways to put it to good use:

Purify water with sunlight (salt and lime juice optional):  UV radiation is sometimes used in municipal water purification systems (more often in Europe).  It doesn’t affect the taste or smell of the water (unlike chlorine), so this is an advantage over that chemical.  However, turbidity of the water (amount of particles present) will decrease the effectiveness of UV radiation, so it should be pre-filtered first.  Here’s where the salt comes in:  if you have a plastic or glass bottle of water that is slightly turbid, add a pinch of salt, which will help the particles settle to the bottom of the container, allowing the UV radiation to penetrate farther into the bottle.   Leave it out in the sun for 6 hours, and the microbes will be dead!  If you want to speed up the process, add some lime juice.  Lime juice cuts down the amount of time necessary to disinfect a two liter bottle of water from six hours to just half an hour!  Limes contain chemical compounds called psoralens, which have been shown to kill pathogens in blood and, now, also in water.  (To Disinfect Water Cheaply, Just Add Sunlight (and Salt or Lime Juice))  Psoralens are also used together with UV light to treat psoriasis, vitiligo, and skin nodules of cutaneous T-cell lymphoma. (National Cancer Institute Dictionary)  Many fruits and vegetables like parsnips, carrots and celery are high in psoralens too, so they would work, but the juice of a lime is probably the most tasty. Of course, the sunlight doesn’t remove pathogens, so if you have the opportunity, you can run the disinfected water through a post-filter. 

Sanitize sheets, bedding and any upholstered item by laying them out in the sun and flipping over after 1-2 hours to expose the reverse side.  UV light kills dust mites and mold!  The key is cleaning off any dirt first (ie, wash anything that can be washed first), and making sure that it dries COMPLETELY in the sun.  Therefore, obviously sheets, quilts and comforters can go in the washer, but bulky items like rugs, mattresses and upholstered chairs should get a vacuuming and surface cleaning using a non-toxic fabric cleaner.  Be aware that sunlight can fade colors, so avoid leaving colorful or fragile items out for more than several hours in direct sunlight. 

“Bleach” plastic containers by leaving them in the sun:  UV light can also take stains out of plastic.  Spaghetti sauce stains be gone!  (Things You Can Clean With Sunlight)

Mildewed things:  Once again, surface cleaning is the important first step in order to get wooden furniture, books, leather, and anything else looking and smelling better.  Then, let the sun do its work!  

Are your air purifiers and emergency supplies ready?  Bad air quality can come from any direction!

“Wildfire season” historically starts June 1, but the concept of a “fire year” is more accurate when fires in Canada begin in April.  This year’s fires in British Columbia and Alberta started in April, and now nearly all of Canada’s ten provinces have fires burning.  The problem for Americans, especially northern states, is that air currents carry the smoke aloft and bring it to remote places, sometimes thousands of miles away.  Certainly people on the mid-Atlantic coast did not expect to see hazy skies or low air quality, but we now know that distant events can wreak havoc on our air quality.  

Take for instance volcanoes.  According to research published in 2018 by scientists at the Imperial College of London, Napoleon’s defeat at Waterloo in 1816 may have in part been caused by a volcanic eruption in Indonesia two months prior.  This eruption of Mount Tambora was the most destructive explosion on earth in the past 10,000 years, killing over 90.000 people and blasting 12 cubic miles of gasses, dust and rock into the atmosphere and over the island and surrounding area.  (Blast from the Past) The ash spewed into the air was carried even higher than it would be by winds alone, due to electrostatic forces.  Negative charges from volcano plume gave the ash a negative charge, repelling it into the air and even as high as the ionosphere, which is a layer of our atmosphere that extends from 50-400 miles above the earth and is responsible for cloud formation.  Even though the charged ash did not reach Europe, it “short-circuited” the ionosphere, initially stopping clouds from forming.  Later, however, the clouds surged back, inundating places like Waterloo which normally only had 2” of rain for the entire month of June.  On 16-18 of June 1815, however, the area received unseasonably heavy rains that made the earth very soft, slowing down cavalry and artillery movements, and delaying the battle on June 18 so that the Prussian forces arrived in time to support the Allies and defeat Napoleon.   This type of cloud suppression was documented following the eruption of another Indonesian volcano, Krakatau in 1883, and reports of ionosphere disturbance followed the eruption of Mount Pinatubo, Philippines in 1993.  

So now we know that volcanoes can interrupt flight schedules, battle plans, and…global rain clouds.  Less rain equals more drought, and more drought equals more wildfires.  When the clouds come back to a drought-damaged area, lightning can spark many fires. In Quebec, for example, fires were sparked by lightning, but officials in Alberta have said that the cause of fires there is currently unknown.  (How did the Canadian wildfires start?)   This is how volcano eruptions can change world events and weather, halfway around the world!  

So, while interruptions to daily activities in the Northeast are hopefully temporary due to the Canadian wildfires, we have to look further to be prepared for the next blanket of wildfire smoke.  Studies regarding erupting volcanoes have shown that they have different atmospheric consequences depending on which hemisphere they are located.  Here are some of the results:

• Scientists studied 54 large explosive eruptions during 501–2000 AD including 16 in the Northern Hemisphere (NH), 25 equatorial and 13 in the Southern Hemisphere (SH).  In the first two years following an eruption, NH volcanoes decrease NH monsoon volume, and SH volcanoes decrease SH monsoon volume.  They tend to have the opposite effect on the opposite hemisphere, for example, a volcano in the NH will increase precipitation in the SH the first year, with diminished increase in the second year.  (Global monsoon precipitation responses to large volcanic eruptions)

• Long-term, however, volcanoes near the equator tend to have greater impacts than the high-latitude eruptions on global climate because their stratospheric aerosol clouds cover a larger surface area and have a longer residence time, and because the aerosols are then transported poleward in both hemispheres and eventually cover the entire globe. (Climate response to large, high-latitude and low-latitude volcanic eruptions in the Community Climate System Model) 

• Volcanoes inject a number of things into the atmosphere when they erupt.  Rocks and larger particles are the first to fall out of the atmosphere, ash can linger for several months, H20 , N2, and CO2 are the most abundant, and sulfur aerosols are responsible for reflecting light back into space and generally cooling the atmosphere. For example, the Pinatubo eruption in 1991 injected an estimated 20 metric tons of SO2 into the atmosphere, leading to a temporary (∼2 years) reversal of the late twentieth century global warming trend.  Did you know that volcanoes also inspire art?  The famous 1893 Edvard Munch painting, "The Scream," shows a red volcanic sunset over the Oslo harbor produced by the 1892 Awu eruption, and the 1815 Mount Tambora explosion inspired the novel Frankenstein by Mary Shelley due to the 1816 “year without a summer” which was unseasonably cold and gloomy. (Volcanic Eruptions and Climate)

• Mount Tonga, an equatorial submarine volcano, released an enormous amount of water vapor high into the atmosphere (mesosphere) when it erupted in February 2022, which caused weather anomalies globally.  Increased rainfall in the southern hemisphere following the jet stream was recorded, and much of the northern hemisphere had drier conditions than average.  (Influence of Volcanic Activity on Weather and Climate Changes)

But non-volcanic activity can be just as dangerous... 

• Halocarbons, used in foam insulation, refrigeration and other appliances, were released during the 2011 Tohoku earthquake in Japan, amounting to 6600 metric tons.  This is an increase of 21-91% over typical levels of six halocarbons that deplete ozone, which in turn affects weather patterns.  (Deadly Japan Quake and Tsunami Spurred Global Warming, Ozone Loss)  Of course, the major headline after this earthquake was the destruction of the Fukushima-Daiichi nuclear plant when the earthquake disabled the power and cooling to its three reactors.  There were no deaths or cases of radiation sickness from the nuclear accident, but over 100,000 people were evacuated from their homes as a preventative measure.  (Fukushima Daiichi Accident)

• Other natural disasters have damaged nuclear plants, like a 1998 tornado that knocked out power to the Davis-Besse plant outside Toledo, Ohio, and Hurricane Andrew, which knocked out power to the Turkey Point plant south of Miami site for five days in 1992. In 2008, Hurricane Gustav damaged the River Bend Nuclear Generation Station in St. Francisville, La.  At both Davis-Besse and Turkey Point, the plants' emergency diesel generators kept the equipment running until crews fixed the power lines. (Can U.S. Nuclear Plants Handle a Major Natural Disaster?)

• The Carrington Event of 1859 was the most intense geomagnetic storm in recorded history.  Earth narrowly missed receiving another series of solar flares in July 2012, which may have exceeded the strength of the Carrington event and prompted widespread power and communications outages. (Carrington-class CME Narrowly Misses Earth) 

It just goes to show that natural disasters can have global consequences.  For the next weather changes and wildfire risks, we could look far and long, or just be prepared with extra filters, masks, food and water, and a well-sealed home.  This is prudent because unfortunately, it only takes one badly-placed volcanic eruption, solar flare, earthquake, hurricane or tornado to upset a nuclear power plant or spew toxins into the air, sending the world and its weather into chaos.  

How can I get more filtration with my current HVAC system?  It’s a tug of war!

At a staff meeting one day, one of our team members related how the HVAC company which installed the central AC system in his new home recommended using the lowest MERV filters available.  I was shocked!  Well, after thinking about it some more, I hypothesized they were waiting for his evaporator coil (the part that transfers absorbs heat from the air by transferring it to the cold refrigerant) to plug up so they could sell him a new system.  In this day and age of availability of every type, face size and thickness of filter, a good HVAC company should be able to work with your existing system to get good filtration.  Period.

If you’ve never heard of MERV, it is an acronym that stands for minimum efficiency reporting value, developed by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) in 1987.    The range is from 1 to 20, and designates with what efficiency the filter removes small particles between 0.3 and 10 micrometers in diameter. (check out this post for more information on MERV).   Generally you’ll want to get the highest rating possible (more filtration) for your system, without causing too much pressure drop, because in general, increasing the MERV increases pressure drop across the filter, while HVAC equipment manufacturers want you to stay with a low pressure drop of around 0.10 inches of water column (i.w.c.) across the filter.  That’s the tug of war–but why aren’t HVAC installers figuring out how to give consumers, the ones who pay for new or upgraded systems, both?  It’s like selling a delicious drink in a cup with a straw that’s too small to get it out at any satisfying rate (like a coffee stirrer).  Sure, you could take out the straw and lid and risk getting it all over yourself as you drink it.  However, even fast food chains and gas stations figured this out years ago: larger straw and cup= convenient way to drink, more satisfaction, more sales.

In this case, though, the consumer is left to bow to the advice of greedy or ignorant HVAC installers, or do research to figure it out himself.  Yes, there is a way to get both high MERV and low pressure drop!  You just need to install a larger filter.  It sounds simple, right?  Yet, because many installers are trained to recommend standard size, 1” filter frames, you’ll probably have to do the math and specify one yourself.  Don’t get scared yet!  We’re here to help with that calculation.  

Here’s a diagram of the typical HVAC system so you know what we’re talking about/aiming for:

Image source: RemoveandReplace.com

The part we’re talking about is outlined in blue.  The filter can be installed on the side of the HVAC closet door, in a ceiling or a wall.  In the diagram the air is flowing through the filter, up through the air handling unit, through the evaporator coil, and out to various room registers/grilles.  The whole system “sucks” air through that filter, and if it’s too small, it’s like sucking a Big Gulp through a coffee stirrer–the pressure drop or suction pressure is too much!  Making the “face” of the filter larger will allow the velocity of the air through the filter to drop, which makes the pressure drop go down.  

So, what is the magic size of filter that makes the pressure drop go down?  That depends on the size of your HVAC system.  This very helpful article from industry expert Allison Bailes gives the secret requirement:  

Filter Area = 2.0 square feet (or more) for each 400 cfm of air flow

Since most filters are measured in inches, we can convert that formula to:

Filter size (sq. inches) = System Air Flow(cfm) x 288/400    OR  

Filter size (sq. inches) = 0.72 x System Air Flow (cfm)

Like in any interesting math problem, this one has a formula with some knowns and some unknowns.  The unknown is the filter size, and the known is the System Air Flow.  To find the system air flow, you can do several things: 

• Look at the HVAC air handler information specifications.  If you don’t have the system specs, go to the air handler, take a photo of the sticker with the model number on it, and search for this model’s manual online.   For example, I replaced my air handler recently with a variable-speed unit.  It will shift fan speeds according to the heating or cooling load, with maximum 1200 cfm, 640 cfm intermediate, and 400 cfm minimum.  Since the pressure drop will be maximum at the maximum air flow, I’m going with 1200 cfm.
• Approximate the air flow using the system tonnage: cooling units are often measured in the US by “tons”.  According to HVACtrainingsolutions.net, 350 to 400 CFM per ton of cooling is required for proper air conditioning system operation. We’ll use 400 cfm to be conservative.  If you know you have a 3 ton system, then 1200 cfm is the maximum airflow.  This lines up with the specifications on my unit.  (This equivalent of 400 cfm per ton can vary because of relative humidity, dry-bulb temperatures, wet-bulb temperatures, air density, mass flow rate, and elevation; if you want to “get technical”, check out this article!)

After you determine the cfm of your system, plug it into the filter size formula above.  In my case, 1200 cfm x 0.72 = 864 square inches of filter.  Yikes!  My own filter (24”x24”) was undersized by a third, and when I measured the pressure drop at maximum fan speed (1200cfm) it was 0.25 inches water gage, which was fairly high for a clean filter. However, if I “upgraded” to a 24x36” filter that size fit my requirements exactly (864 square inches).  The problem is that I don’t have room for such a big filter.

If you find that space or filter availability for bigger filters is a problem, you can solve it in a different way: add another return with another filter.  Many homes have 2 returns, such as one upstairs and one downstairs.  In this way, you’re getting the area and the filtration you need.  Adding a second return lowers the airflow per return, and also changes the air circulation in your home.  At the minimum, high MERV and high airflow will not be a problem!  In my case, the easiest thing to do was look at the return air duct and add another grille in the only place I could: my bedroom.  I ended up adding a 20x20 return air grill there, which lowered the pressure drop to 0.09 inches water gage for a clean filter, which eased the work of the fan unit and gave me more filtration.

This is the dilemma homeowners often face: accept the “expert” opinion of their contractor, or start doing their own research and demand equipment or installations that at least safeguard the equipment they are installing!  Many installers mean well, but by not using standard equipment like manometers (pressure-sensing devices) they have no idea what the pressure drop over the filter is.  They also don’t know what pollutants like dust, human and pet dander, and microbes are allowed  into the new system by specifying low-grade MERV filters.  Their ignorance or bad advice costs homeowners BIG when the air, and consequently the system, stays dirty.  Just like we sometimes must do with our health and doctors, we hope that you take this information to your HVAC company and specify what you need to win the tug-of war and keep you and your family healthy!