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Duct Hunting Season: Killing Pollutants in HVAC System

By Martha Michael

Seasonal weather changes bring new activity to the forced air systems in the home and workplace, reminding us that it may be time to check for air pollutants inside the house. The need for indoor air purity isn’t just a game, it’s a serious issue. But is routine cleaning necessary?

Getting your heating, ventilating and air conditioning, or HVAC, systems cleaned involves a number of components, says the website for the U.S. Environmental Protection Agency:

  • Air ducts and registers
  • Grilles and diffusers
  • Heating and cooling coils
  • Drain/drip pans
  • Fan motor and housing
  • Air handling unit housing

The Process

Over time, particles may collect in ducts, and when combined with moisture, mold can form and spores may be released into the house through vents. If your HVAC system isn’t maintained, parts of the system can be contaminated, which can be the cause of allergy symptoms. 

There are various methods for cleaning your system. Technicians have tools designed to loosen the dirt from ducts and usually follow up with industrial strength vacuums. There are chemical combatants also, biocides to kill any mold that’s forming. Sometimes sealants can be applied inside ducts to inhibit the formation of microbial growths also.

The EPA website says a cleaning service can range between $450 and $1,000, and prices vary according to:

  • Services hired
  • System’s size
  • System’s accessibility
  • Climate in your area


The problem is a lack of research as to the efficacy of these kinds of measures, says the EPA, and it’s underscored in an article by the Division of Occupational Health and Safety, or DOHS, on the National Institutes of Health website. There has been some focus on HVAC contamination in the last 20 years, but not much verification.

“The review did find clear evidence that ductwork can be contaminated with dust and can act as a reservoir for microbial growth under normal operating conditions,” says the DOHS. “Yet, even when duct cleaning was extremely efficient at removing contaminants within ducts, the effectiveness of reducing indoor air pollutants was highly variable.”

Though there’s little evidence to prove that routine duct cleaning is absolutely necessary, there’s still a case for prevention.


The NIH suggests consumers comply with manufacturer’s recommended schedule for maintenance. If you're remodeling, be sure contractors seal the ducts. Also, practicing proper housekeeping will limit the possibility of contamination.

The EPA suggests homeowners consider routine cleaning or even duct replacement in the following cases:

  • If ducts have water damage
  • Growth of microbes
  • Debris in ducts
  • Dust discharge
  • Odors in ducts

Cleaning HVAC ducts is the last step, says the DOH. First the problem has to be evaluated and the origin of contamination located. That way there’s little chance of a recurrence.

The sparse conclusions by experts shouldn’t cause us to be apathetic toward getting our HVAC systems cleaned. There may be a lack of evidence from research, but it would be a shame to shoot down a good idea.


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