What Air Duct Cleaning Includes (and What It Doesn't)

The parts of the system a full cleaning should cover

Your heating and cooling system moves air in a loop. Return ducts pull air from the rooms back to the air handler, the air passes through the filter, blower, and heating or cooling equipment, and supply ducts carry it back out to the rooms. Dust and debris can settle anywhere along that loop.

EPA advises making sure the service provider agrees to clean all components of the system. Cleaning only the ducts, or only the vent covers, leaves parts of the loop untouched, and EPA notes that failing to clean a component of a contaminated system can recontaminate the entire system.

Source: U.S. EPA: Should You Have the Air Ducts in Your Home Cleaned?

How the work is usually done

Duct cleaning is mostly mechanical: dislodge the dirt, then capture it. EPA describes providers using specialized tools to loosen dirt and debris and a high-powered vacuum to remove it. The details below are the practices EPA says a provider should follow.

• Open access ports or doors so the entire system can be cleaned and inspected.
• Check for asbestos-containing materials, such as some older insulation or register boots, before starting. EPA says these need specialized procedures and should be disturbed only by specially trained and equipped contractors.
• Use vacuum equipment that exhausts particles outside the home, or HEPA vacuuming equipment if it exhausts indoors.
• Protect carpet and household furnishings during the work.
• Use well-controlled brushing of duct surfaces together with contact vacuuming to dislodge dust and other particles.
• Use soft-bristled brushes on fiberglass duct board and fiberglass-lined ducts.
• Seal and re-insulate any access holes made to reach the ducts, so the system stays airtight.

Source: U.S. EPA: Should You Have the Air Ducts in Your Home Cleaned?

What duct cleaning does not include

Cleaning removes accumulated dust and debris from the parts that are cleaned. It is a different job from fixing, replacing, or treating the system, and it helps to know where those lines are before you compare offers.

• Duct sealing and repair. Leaky, disconnected, or kinked ducts are fixed by sealing with mastic or metal tape and repairing or insulating ducts. ENERGY STAR treats this as duct improvement work and notes that most heating and cooling contractors also repair ductwork.
• Mold diagnosis and remediation. EPA says only an expert can confirm whether suspected growth is mold, that insulated ducts with mold should be removed and replaced rather than cleaned, and that the moisture problem has to be fixed or the mold will likely return.
• Pest control. If ducts are infested with rodents or insects, EPA says the cause has to be corrected before cleaning or the problem is likely to come back.
• Routine chemical treatments. EPA notes that only a small number of biocide products are registered for use inside bare sheet metal ducts, none for fiberglass duct board or fiberglass-lined ducts, and that sealants are not recommended for routine use.
• Furnace, air conditioner, gas, or electrical repair. Those are separate trades. EPA recommends that fuel-burning furnaces be inspected and serviced before each heating season to protect against carbon monoxide, which is a different job from cleaning ducts.
• A health treatment. EPA states that duct cleaning has never been shown to actually prevent health problems.

Sources: U.S. EPA: Should You Have the Air Ducts in Your Home Cleaned?; U.S. EPA: A Brief Guide to Mold, Moisture and Your Home; ENERGY STAR: Duct Sealing

Questions to ask before work starts

Not every offer labeled duct cleaning covers the same parts, so agree on scope in writing. EPA recommends getting a written agreement that outlines the total cost and scope of the job before work begins.

• Which components are included: supply ducts, return ducts, registers, blower, coil, drain pan, plenums?
• What vacuum equipment will be used, and does it exhaust outdoors or through HEPA filtration?
• How will you get into the ducts, and how will access openings be sealed and re-insulated afterward?
• If you say there is mold or other biological growth, will you show it to me? (EPA recommends asking.)
• Is anything in the estimate a repair, replacement, or chemical treatment rather than cleaning?

Source: U.S. EPA: Should You Have the Air Ducts in Your Home Cleaned?

How to check the job afterward

EPA publishes a checklist for judging whether a cleaning was done properly. You do not need tools beyond a flashlight to check most of it, and a provider doing careful work should not mind you looking. The points below cover the parts that were in your agreed scope.

• Ductwork is visibly clean when you look inside at several random spots.
• If the coil and drain pan were included, both sides of the coil look clean and the drain pan is clean and draining.
• The blower blades and blower compartment are free of debris.
• Supply and return plenums are free of visible dust and moisture stains, and filters fit properly.
• New access doors in sheet metal ducts are attached with more than just duct tape, such as screws, rivets, or mastic.
• Registers and grilles are firmly reattached.
• The system runs normally in both heating and cooling modes.

Source: U.S. EPA: Should You Have the Air Ducts in Your Home Cleaned?

Keeping the system cleaner afterward

EPA says the most effective way to prevent duct contamination is to keep dirt and water out of the system in the first place. These habits cost little and apply whether or not you ever schedule a cleaning.

• Use the highest-efficiency filter your system's manufacturer recommends, change it regularly, and change it more often if it clogs quickly.
• Make sure the filter fits snugly, with no gaps that let air bypass it.
• Repair water leaks promptly and make sure the condensate pan drains.
• Make sure ducts in unconditioned spaces such as attics and crawlspaces are sealed and insulated.
• During dusty renovation work, seal off supply and return registers and do not run the system until the dust is cleaned up.

Sources: U.S. EPA: Should You Have the Air Ducts in Your Home Cleaned?; U.S. EPA: Guide to Air Cleaners in the Home