You’ve probably seen advertisements from companies offering to improve your home's indoor air quality by cleaning your air ducts. This can include cleaning various heating and cooling system components of forced air systems, including the supply and return air ducts and registers, grilles and diffusers, heat exchangers, heating and cooling coils, condensate drain pans (drip pans), fan motor and fan housing, and the air handling unit housing.
If you have your heating and cooling system cleaned, make sure the service provider agrees to clean all components of the system and is qualified to do so. Failure to do so can result in re-contamination of the entire system, negating any benefits.
Some service providers may also suggest applying chemical biocides, designed to kill microbiological contaminants, to the inside of the ductwork and other system components. Others might apply chemical treatments (sealants or other encapsulants) to seal or cover the inside surfaces of the air ducts and equipment housings, which controls mold growth and prevents the release of dirt particles or fibers from ducts. These practices haven’t been fully researched, so educate yourself before taking this route.
Since knowledge about the potential benefits and problems of air duct cleaning is limited, it’s impossible to generalize whether air duct cleaning will benefit you.
If no one in your household has allergies or unexplained respiratory symptoms or illnesses, and if you see no visual indication that your air ducts are contaminated with large deposits of dust or mold (no musty odor or visible mold growth), you probably don’t need to clean them. It’s normal for the return registers to get dusty as air is pulled through the grate. This doesn’t mean your air ducts are contaminated; the registers can be easily vacuumed or removed and cleaned.
On the other hand, if family members are experiencing unusual or unexplained symptoms or illnesses you think might be related to your home environment, discuss the situation with your doctor. You can also visit the EPA’s website for more information.
Of course, you may consider cleaning your air ducts simply because you think they’ve grown dirty over time. While the debate about the value of periodic duct cleaning continues, no evidence suggests it would be detrimental, provided it’s done properly.