It may surprise many of you to learn that cleaning your HVAC ducts may actually increase the amount of particulate mater in the air and lead to actually more contaminated air being delivered to the home.
This seems at first glance to be too preposterous to be true—and I must admit that I had to “re-educate” myself as to how ducts function under normal operating conditions. (This discussion also is not applicable to ducts that have water, mold or vermin intrusion.)
Dirt that accumulates on the inside of your ductwork does so because the dirt falls out of the air as the air moves through the duct. In a sense the ductwork itself acts as a filter. Really clean ducts don’t filter as much air thus there is more particulate available to enter the house and/or clog the furnace filter. Obviously really good filtering systems are a good idea, but no standard furnace filter is very effective and even the best filters are not 100% effective.
When ducts are cleaned, care needs to be taken to ensure as little impact as possible on the occupants of the home from the chemicals used in the cleaning process and from particulate stirred up in the cleaning process. A really excellent treatise on the wisdom of duct cleaning can be found at: Duct Cleaning for Quackers by Caoimhín P. Connell, a Forensic Industrial Hygienist.
There is also this article from the EPA, Should You Have the Air Ducts in Your Home Cleaned?: “Duct cleaning has never been shown to actually prevent health problems. Neither do studies conclusively demonstrate that particle (e.g., dust) levels in homes increase because of dirty air ducts or go down after cleaning. This is because much of the dirt that may accumulate inside air ducts adheres to duct surfaces and does not necessarily enter the living space.”
When ducts become so clogged that air flow starts to be affected, cleaning is obviously necessary, but cleaning your ducts too often may actually make your home “less healthy”. The duct in the following picture, in my opinion, needs cleaning, but one can get the idea how all the convolutions of the built-up lint acts as a filter—a place where particulate can drop out of the air stream and be collected.
Charles Buell, Seattle Home Inspector
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