Concentration of CO2 in the Atmosphere

Indoor Air Quality: Some Things to Know:

Diagram explaining how a heat recovery ventilator works. Image: Greentek

Michael Canavan

This article is a follow-up to “Understanding the Blower Door Test” published in the January 2020 issue of G.E.T.

Now that you have sealed your house as recommended from your blower door test results and verified that your house has an air changes per hour (ACH) rating of three or less, you are feeling warm in your draft- free home. But the indoor air quality of your home may not be as good as it was in your drafty house. You can take the next step to improve the indoor air quality by installing a controlled ventilation system.

Indoor air quality is influenced by environmental and mechanical factors. Environmental factors in the home include trapped moisture levels, off-gassing of building materials, paints, furnishings, cleaning products, smoke, and human bodily functions. Mechanical factors can include combustion byproducts and fuel storage.

Combustion byproducts are generated inside your home from heating equipment and cooking. Your heating equipment should be serviced and inspected on a yearly basis for proper combustion, ventilation, and overall condition. The heat exchanger in the furnace may begin to deteriorate and develop a hole. When you are cooking food on your stove or in your oven, you may be burning gas which has carbon monoxide as a byproduct and, on the rare occasion that you burn the food, you may be releasing other unwanted products into the air of you home. This is why you should have an exhaust hood over your stove that vents to the exterior of the home.

Moisture levels in the home come from washing, cooking, breathing and ground conditions. The relative humidity of a home should be between 30% and 50%, so moisture does not create breeding grounds for mold. When you buy new materials and bring them into your home, they have different chemicals on them that you can smell. This process of releasing chemicals in the home is called “off-gassing” and can lead to health issues. The plywood used in building your home and some furniture can take two years to outgas the formaldehyde in it. Some paint products have volatile organic compounds (VOC) in them; look for low or zero VOC painting products whenever possible. Cleaning products have ammonia, chlorine bleach, vinegar and petroleum products, as the basic cleaning materials with added aromas to make them more pleasant smelling. These materials, in enclosed unvented spaces, can become overwhelming to the point of making you sick quickly. Smoking indoors puts tar and carbon monoxide into the air along with other pollutants.

The way you control the moisture and pollutants in the air of your sealed home is to install proper ventilation, local exhaust fans, and a whole-house ventilator system. The three basic whole house ventilator system types are air exchangers, ERVs – energy recovery ventilators, and HRVs – heat recovery ventilators. The air exchanger is a fan unit that filters and mixes indoor air and outdoor air, and then expels some of the indoor air out of the house. This system runs slowly, at 60 cubic feet per minute (cfm), and though less efficient at removing stale air, it is the least expensive system.

ERVs are recommended for climates where the main concern is cooling, such as the Gulf coast region of the country. They are a moisture and heat recovery unit. ERVs have a moisture-permeable membrane to allow moisture to be removed from the air stream.

HRVs are used in heat-requiring climates like ours. The unit works by passing air through an air exchanger which allows for the warm indoor air to give up its heat as it exits to the cooler incoming air in the heating season and does the opposite during the cooling season. The outgoing air and incoming air are blown through separate air channels to allow this exchange to take place. There are two types of exchangers: flat-panel (vertical or horizontal) with 50% and up to 80% efficiency, respectively, and cellular which can be up to 80% efficient, with cost increasing with efficiency.

These systems can be installed in a home with or without a central air furnace system, as long as there is space to install small duct runs. With the installation of a ventilator system you will breathe easier knowing that the air in your home is cleaner and you are saving on your energy costs.

Michael Canavan is the owner of Eagle Home Inspection Solutions of Norwich, Vermont. Learn more at, or (802)526-2642.

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