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When to clean ducts
“Get your air ducts cleaned, don’t get taken to the cleaners...”
In houses that produce voluminous amounts of dust and mold, ducts might need cleaning every few years. But in most homes with reasonably modern furnaces and air conditioners, where filters are replaced regularly, a professional cleaning is rarely, if ever, required.
If no one in the household suffers from allergies or unexplained symptoms or illnesses, and if a check under the registers does not reveal large deposits of dust or mold, cleaning is probably not necessary, according to the EPA. You should consider having air ducts cleaned if there is a noticeable buildup of dirt and dust despite regular filter changes, and if there is substantial and visible mold growth inside the ducts even though the appliances are well maintained.
The cleaning decision also can be affected by the type of ducts you have: traditional sheet metal, nonmetal ducts made of fiberboard, or any type of duct (often flexible ductwork) that has some type of internal liner.
Though there are disagreements, the EPA says current research indicates that all types of ducts support microbial growth to approximately the same degree. But there are some distinctions. One is that moisture can be trapped in some insulated duct systems, which have to be kept reasonably dry to retard mold growth. This is not much of a problem in bare metal ducts that have no liner or porous material to trap moisture.
It's also easier to treat mold contamination on bare sheet metal than on other types of ducts. Contractors can use an EPA-registered biocide (often called a sanitizer) on bare metal.
But once a fiberglass duct liner is contaminated with mold, cleaning is not sufficient to prevent regrowth, according to the EPA. One obvious reason: No products are currently EPA-registered as biocides for use on fiberglass duct board or fiberglass-lined ducts. Both the EPA and the Washington-based National Air Duct Cleaners Association (NADCA) recommend replacing wet or moldy fiberglass duct material.
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