Last Updated: Feb 16, 2021
In North America, we have a love affair with forced-air heating systems. These industry-standard mechanicals supply heating, cooling, and ventilation through ductwork snaking through our homes. Is this the healthiest system we can have within our homes? If you have forced-air heating systems, here’s what you need to know.
Ductwork is metal or synthetic tubes that transport air from heating or cooling equipment throughout your home. Properly installed and well-maintained ductwork is an essential component of healthy indoor air quality and comfort. Clean ductwork reduces the number of allergens and irritants in the air, removes unwelcome odors, and improves airflow efficiency. We'll get into specifics later in the article.
In some climates, we run our ductwork in the attic or the crawlspace. These spaces can be very hot in the summer when we are pumping cold air through the ducts; conversely, in winter, very cold when trying to move warm air to our living spaces. This dramatically reduces the efficiency of your furnace, as it must run longer to deliver the conditioned temperate air to your home. The air quality is also impacted, as the ductwork in these areas is rarely airtight. This means that air from the attic or the dirt in the crawlspace can be drawn into the airstream, bringing dust and microbial creatures. To be effective, the ductwork in these spaces should be airtight and should have as much insulation around them as the space they are in; meaning if you have R-60 in the attic, the ductwork should be surrounded with R-60 insulation. Follow these tips to insulate your attic properly.
The newer high-efficiency furnaces with smaller flexible plastic ductwork are not cleanable, ever. This ductwork is supposed to be installed very tightly, so no dips or sagging from the coils are present. The air quality concerns are that the ductwork's improper installation will create pockets where dust will tumble out of the airstream and elevate particulate matter in your home. Cleaning this ducting could lead to tears in the plastic, making the air quality and efficiency much worse within your home.
The short answer is no. As the air moves through the ductwork, it does pick up the particulate that isn't held down by the manufacturing oils. These ultra-fine particles are aerosolized within our living spaces. These may contain construction dust, dander, pollens, skin and hair cells, chemical dust, and many other elements. Forced air systems blow these allergens and toxicants around the home, and the dust eventually settles in carpets and on surfaces.
The average duct cleaning company recommends at least once a year. Both the U.S. Environmental Protection Agency (EPA) and Canada Mortgage Housing Corporation (CMHC) do not recommend cleaning your ductwork. As a healthy home consultant who has seen hundreds of systems in homes, I recommend cleaning ductwork every 5-7 years or after significant renovations. The research is solid from both organizations, as they rightly assessed the manufacturing oils on the inside of the ductwork will hold dust and take it out of the airstream. Unfortunately, once the ducts' dust becomes thicker and thicker (think inches), then all bets are off.
You can inspect your ductwork yourself with your cell phone and take a photo of the ducts. The debris field is typically within the first 4 feet of the outlet, and you can reach those with a shop vacuum hose. The kitchen, dining room, and bathroom will be the dirtiest, so start there. The air return (the sucking side of the ductwork) will be dirtier than all the others, so ensure you clean that area as well.
If you have a fiberglass duct board, the fibers can be released into the air stream and cause air quality concerns. When doing any renovation where the duct board is exposed, consider replacing them.
Forced air, by its very nature, dries the air out. This dry air increases the likelihood of illness by drying up your mucus membranes' natural ability to trap and remove viruses. Dry air also increases the static electricity potential in the house, mostly where carpets are located. As the air moves through the ductwork, electrons can be scraped off the air molecules. This imbalance increases static electric shocks we feel when we grab a door handle or touch another person.
Unfortunately, whole-house humidifiers are mostly ineffective at delivering moisture to the entire house. Furnaces are designed to make air hot, not moist. The older drum style has a higher chance of growing bacteria and other biological creatures in the trays; for this reason alone, they are not recommended. Newer drip-style humidifiers are better in this aspect but are still not effectively adding moisture to the air. Air sealing your home and using standalone humidifiers in bedrooms and other high-traffic rooms will add necessary moisture to your home's air.
Forced air systems are not ideal for our health. They bring particulate into our homes and create temperature discomfort through stratification. Periodic inspection and cleaning after major renovations will improve the air quality in the house. When ductwork is outside conditioned space, air sealing and insulating the ductwork will yield dramatic energy efficiency improvements. Using ceiling fans to push the heated air down will improve thermal comfort. If building new, consider more biologically ideal heating systems such as radiant heat.
Stephen Collette is a Building Biologist, Building Science Consultant, LEED Accredited Professional, and a Heritage Professional. Stephen is the owner of Your Healthy House and lives in Lakefield, ON with his wife and 2 daughters.