Some physicians, such as Ashcrafts, tell patients to-go because of it. Others arent as positive. Ive had people practically repair their residence, said Dr. Donald McNeil of Midwest Allergy and Immunology. He doesnt usually propose air-duct-cleaning because what settles in the tubes isnt always circulating through the air. For most of us, greater purchases are removing carpet from the bedroom, replacing mattresses each seven years and replacing furnace filters often, McNeil said. The EPA does suggest duct-cleaning if theres significant mold growth, or a rat or insect infestation, or if the ducts are clogged with debris and excessive dust. Sometimes, duct products will advise applying a biocide to the inside the tubes to kill viruses and mold.