Air duct cleaning cost (and when it's worth it)

The EPA says the price depends on the services offered, the size of the system, how easy it is to reach, the climate region and the level of contamination. A home with two systems, long duct runs or ducts in a tight crawlspace sits toward the high end.

Be wary of very low advertised prices.

This is the honest part. The EPA's guidance says duct cleaning has never been shown to actually prevent health problems. It says duct cleaning is not considered a necessary part of yearly maintenance of your heating and cooling system. The EPA does not recommend that air ducts be cleaned except on an as-needed basis.

A light layer of dust on a return grille is normal. Dust inside ducts mostly sticks to the duct walls and does not necessarily enter your rooms. A clean filter, changed on schedule, does more for your air and your equipment than a yearly duct cleaning.

The EPA says to consider cleaning in these cases:

• There is substantial visible mold growth inside hard-surface ducts, such as sheet metal, or on other parts of the system.
• The ducts are infested with vermin, such as rodents or insects.
• The ducts are clogged with excessive dust and debris, or particles are actually released into the home from the supply registers.

Two points matter here. First, ask the contractor to show you the mold or debris. If you are unsure whether a substance is mold, a lab can test a sample. Second, fix the cause. Mold comes back if the moisture stays, and the EPA says wet or moldy duct insulation cannot be effectively cleaned and should be removed and replaced. Ducts in that condition may be a replacement job. See the ductwork replacement cost guide for that.

After a renovation that sent drywall dust or sawdust into open ducts, a one-time cleaning is also reasonable.

• An inspection before the work, with photos of what was found.
• Cleaning of the whole system: supply and return ducts, registers, the blower, the coil and drain pan, and the air handler cabinet. Cleaning only the ducts leaves the dirtiest parts untouched.
• Protection for your floors and furnishings, and a vacuum that exhausts outside or uses HEPA filtration.
• Care with fiberglass duct board and flex duct, which damage easily.
• Photos after the work, and a written, fixed price before it starts.

Chemical treatments are the most common upsell. The EPA says no chemical biocides are currently registered for use in internally insulated air duct systems, and that research has not demonstrated the effectiveness of these products in duct cleaning or their potential adverse health effects. It also says sealants should never be used on wet duct liner, to cover actively growing mold, or to cover debris in the ducts.

Before any biocide is used, the EPA says the provider should show you visible evidence of microbial growth and explain why it cannot be removed by physical means such as brushing. If a company insists on spraying as a standard step, decline it. More pricing help is in the HVAC cost guides.