Air duct cleanings should take place every three to five years. People moving into a home should have the air ducts cleaned unless they know the service has taken place in the last three years. After a remodeling project, it's wise to clean the sawdust out of the ducts.
Cleaning air ducts cuts down on the amount of bacteria and mold within the system. It also reduces the dust sitting on the surface of return-air ducts, although its benefits for supply-air ducts are less tangible. The best method involves cleaning the fan on the air handler/furnace and the return-air ducts only.
Duct cleaning providers are not certified by the EPA, but consumers can check with local agencies to learn whether they are licensed. The EPA warns people to be wary of any duct cleaner who either claims the service provides health benefits or attempts to use chemicals. The agency also suggests contacting the references of duct cleaning professionals before hiring them.