Breathe Healthy Air In Your Home

By Tim De Stasio

Right now, many home owners are concerned about breathing healthy air. It’s April, 2020 and the Coronavirus is spreading through the country, causing many people to have increased awareness about their respiratory health.

I want to be very clear about the intent of this article. I am not a medical professional, nor am I certified to diagnose or remediate mold. I am a licensed HVAC professional and a Building Performance Institute (BPI) Home Performance Contractor that has done a lot of research to give my customers educated solutions to their indoor air quality (IAQ) concerns as these are impacted by their HVAC system. I hope to share these findings with you.

What Are Causes of Poor Indoor Air Quality?

Airborne pollutants are the cause of poor air quality.  These pollutants can be classified into 2 basic groups: Particulate Matter (PM) and Gaseous.  Particulate Matter pollutants include organic chemicals, soil and dust particles, pollen, viral and bacterial organisms, dust mites, animal dander and others.  Gaseous pollutants include carbon monoxide, tobacco smoke, ozone, Volatile Organic Compounds (off- gassing of chemicals) and radon.  These 2 groups are very different in their composition and must be handled differently as well.

Four Strategies to Improve IAQ

4 Strategies to Improve IAQ

  1. Eliminate the source
  2. Ventilate
  3. Filter
  4. Control humidity

Eliminate at the Source. The best strategy to improving air quality is to remove the source of pollutants before they ever enter the home. That leaves less work for your HVAC system to remove pollutants. For example, using natural building materials that don’t off- gas, not smoking indoors, not allowing pets to come inside, keeping humidity levels low, etc. 

Your home’s attic, basement and crawlspace are dirty areas. Never store chemicals in these areas, rather store them in a building that’s not attached to your house. This lowers the concentration of pollutants that can enter the home.

Sealing your home’s envelope and ducts are critical to eliminating pollutants at the source. These are pathways that can allow dirty air to enter the home. Sealing these leaks may seem easy, but understanding where these hidden pathways are and being willing to crawl and climb to access them requires a professional with the experience and training to do so effectively and completely. Hiring a BPI certified Home Performance Contractor is the best way to effectively seal your thermal envelope and ducts.

Ventilation. The second strategy is to dilute these pollutants by mixing cleaner, fresh air from outdoors. This can be done by opening windows or mechanically introducing outside air through your HVAC system.

Opening windows in many climates is simply not realistic. It may be too hot or cold outside. Or there may be pollen or other pollutants that would defeat the purpose. Introducing outside air through the HVAC system allows this air to be filtered, heated, cooled and dehumidified before entering your home.

An HVAC professional should install a ventilation system that is right for your home. One of the most economical ways is called “Positive Ventilation”. A small duct from the outdoors is connected to your HVAC return. There is a motorized damper driven by a controller that ensures fresh air only is introduced when the system is running and the outdoor conditions are favorable to do so. Another more expensive strategy is “Balanced Ventilation”, where fresh air is introduced using an “Energy Recovery Ventilation” unit and mixes with exhaust air being pulled out of the house, usually replacing bathroom fans. There are pro’s and cons to both strategies and a knowledgeable HVAC professional can explain these.


It is impossible to prevent all pollutants from entering your home. Your HVAC filter can catch particulate matter, but it cannot catch gaseous pollutants. Most air filters are given a MERV rating.  MERV stands for Minimum Efficiency Reporting Value.  The higher the MERV rating of a filter, the more efficient it will be, meaning it will catch more particulates.  However, the more efficient the filter is, the more resistance it can put on the HVAC system.  Typically a MERV 8-11 filter provides excellent filtration, while not sacrificing airflow performance.

During mild weather, an HVAC system may not run as often.  The air filter can only do its job if the system is running.  So it is advisable to run the HVAC fan periodically during mild weather to allow the air filter to do its job.  Replacing air filters often will also improve IAQ.  However, while air filters address particulate matter like dust, they are not effective against some fungal and bacterial organisms which can be too small to be caught by the filter.

How Air Filters Are Rated

Air filters manufacturers use different scales to measure efficiency and effectiveness.  Below is a quick guide to help you understand some of the more common ratings.

MERV– Stands for Minimum Efficiency Reporting Value and is most commonly used. MERV 8 should be the minimum value used in a home, while MERV 11 and 13 filters provide excellent filtration, up to 90% of particulates 3-10 microns.

MPR -Stands for Micro Particle Performance Rating and is proprietary to the 3M brand filters. MPR 600-1200 is a similar range to MERV 8-11.

FPR– Stands for Filter Performance Rating and is used by The Home Depot and Honeywell to rate filters.  FPR 5-7 is comparable to MERV 8-11.

HEPA– Stands for High Efficiency Particulate Air filter. It can capture up to 99.7% of particulates 3-10 microns. Typically, a HEPA filter is not necessary or recommended for a residential HVAC system since the excessive airflow resistance can create mechanical problems.

Humidity Control

Fluctuations in weather can make controlling indoor humidity levels difficult. In humid climates, this is especially challenging. Moisture moves from humid to dry, so during humid weather, the humidity is trying to enter your home from outside. Your home’s AC system removes humidity, but sometimes not enough. A BPI certified Home Performance Contractor can properly seal your home’s thermal envelope and duct system to reduce how much humidity leaks into the home.

Controlling humidity is important because research shows that relative humidity over 60% and under 35% are optimal conditions for biological growth. Making sure your HVAC system is performing correctly is essential to keeping indoor humidity between 35 and 60%. In some cases, a whole house de-humidifier or humidifier can be installed to supplement the HVAC system.

Air Purifiers, Scrubbers, UV Lights- Do They Work?

The simple answer is, yes, they can be effective. As mentioned earlier, the best way to reduce or eliminate these pollutants is preventing them from entering the building in the first place.  However, sometimes, these pollutants are present despite efforts to prevent them. In that case, I recommend using some or all the these technologies.

UV Lamps.  This technology is known as Ultra Violet Germicidal Irradiation (UVGI).  It is based on the principle that the earth naturally cleans itself by using, among many things, the sun’s ultra violet waves to kill unwanted organism growth.  UVGI lamps are designed either to kill growth on HVAC coils and other surfaces.  They are only effective on the surfaces that the bulb is shining on. Typically, these are found on HVAC evaporator coils since they can become a breeding ground for bio growth.

PCO or Photocatalytic Oxidation uses a chemical process and a UV lamp to convert gaseous pollutants into carbon dioxide and water.  The construction of a PCO purifier is important.  It must be constructed in a way that gives the pollutants enough “dwell time” in contact with the UV lamp to be effective.  It is important to note that some studies have shown that PCO purifiers can create unwanted side effects like formaldehyde- a known carcinogen. It’s best to use these as a preventative measure after the 4 above mentioned strategies have been employed. The less pollutants in the air will deliver more consistent results.

Ionizing air cleaners electrically charge gaseous pollutants which changes their composition. One important factor to consider with all these air cleaning devices is what the byproducts are.  One harmful byproduct is excessive ozone which is known to cause respiratory problems.  When selecting any air cleaner, purifier, ionizer or other similar device, always look for one that does not create ozone.

It is also important to mentioned that at the time of this article, none of these technologies have been proven to eliminate COVID-19, or Coronavirus. Breathing clean, healthy air is possible. Using common sense methods and technology are effective as long as these are based on science. As always, doing your research, consulting knowledgeable professionals and making an educated decision as a consumer will yield the best results.

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