The EPA's consumer document Should You Have the Air Ducts in Your Home Cleaned? is the closest thing to an official federal position on residential duct cleaning. Its core message is restraint: the EPA says duct cleaning has not been shown to prevent health problems, and that dirt sitting in ducts is not necessarily a problem on its own.
Instead of a calendar schedule, the EPA recommends cleaning for a specific cause: visible mold growth inside the ducts or on other HVAC components, ducts infested by vermin, or ducts clogged with substantial debris that's actually being released into the home. Absent one of those, the agency suggests cleaning may not be necessary.
The EPA also cautions about the upsell layer of the business — chemical biocides and sealants applied inside ducts — noting their long-term effects are not fully understood and that they should only be used after careful consideration. For a homeowner, the practical takeaway is to treat 'your ducts are filthy, you need a full sanitizing' cold pitches with skepticism and ask for evidence of an actual problem first.