If you or someone in your family suffers from asthma or allergies, you may be considering getting your home's heating and cooling ducts cleaned. But even if you have no special health concerns, duct cleaning may appeal to you at an intuitive level. After all, if your ducts are clean, all that air flowing out of your vents should come out clean too, right?

Well, actually, no.

Companies that perform duct cleaning would love you to believe you need their services. Some might even advertise health benefits, or suggest that duct cleaning will lower your power bills by improving your system's efficiency. Some ads even use such language as, "Studies have shown …" But no data back up these claims. Even if your ducts are very dirty, cleaning them likely won't provide any measurable benefits. In fact, the little independent research performed on duct cleaning indicates that the process stirs up so much dust that it creates a bigger problem than it solves.

How duct cleaners work

Companies connect a powerful vacuum to one or more openings in the ductwork to suck out loose dust and other debris. Because lots of dust can cake on the inside of ducts, firms use a variety of methods — a rotary brush or compressed air nozzles, for example — to shake it loose.

Many duct-cleaning companies also offer services you can get from conventional heating/cooling firms such as cleaning heat exchangers and cooling coils.

The case against having your ducts cleaned

Here's the thing: Dust that settles in your ventilation ducts typically stays there unless disturbed, and is usually harmless.

The official advisory of the U.S. Environmental Protection Agency (EPA) concludes: "Duct cleaning has never been shown to actually prevent health problems. Neither do studies conclusively demonstrate that particle (e.g., dust) levels in homes increase because of dirty air ducts. This is because much of the dirt in air ducts adheres to duct surfaces and does not necessarily enter the living space. … Moreover, there is no evidence that a light amount of household dust or other particulate matter in air ducts poses any risk to your health."

The American Lung Association has a similar position.

Having your ducts cleaned may actually create a dust problem or make an existing problem worse. In the 1990s, the Canada Mortgage and Housing Corporation (CMHC) tested 33 homes in Montreal before and after duct cleaning, finding no significant improvement in air quality and that duct cleaning alone did not improve airflow or energy efficiency. In some cases, measured particle levels actually increased immediately after a cleaning. In other cases, particle levels decreased immediately after cleaning, but returned to previous levels within weeks.

If you suspect a mold problem — either because of visible growth or a musty smell consistently coming from supply vents — cleaning ducts won't do much good if it doesn't eliminate the mold. Mold always begins with a moisture problem, and the ducts themselves are unlikely to be the source of the problem. The most likely culprits are the cooling system's evaporator coils, which your heating and air-conditioning contractor — and most duct-cleaning companies — can inspect and maintain. Leaky return ducts can also introduce moisture.

Want to control dust? Regularly change your filter

Frequently changing air filters is the best way to keep dust, allergens, and other particles out of your home. Most should be replaced every two or three months.

Duct cleaning won’t save energy, either

Another sketchy claim made by most duct-cleaning operations and their trade association is that dirty ducts and equipment overburden heating and cooling equipment, which wastes energy. Again, it intuitively makes sense that a cleaner system will run smoother and last longer — after all, that's why we and HVAC equipment manufacturers and repair services recommend that you regularly change your filters. But the page "Benefits of HVAC Cleaning" on the National Air Duct Cleaners Association (NADCA) website stretches this benefit too far by stating: "According to the U.S. Department of Energy, 25 to 40 percent of the energy used for heating and cooling a home is wasted."

That's misleading.

Although much of the energy used to power heating and cooling equipment is indeed wasted, that waste is due to inefficient equipment, lousy insulation, leaks around doors and windows, and unsealed ductwork. While there's some benefit to cleaning and maintaining HVAC equipment, that benefit is relatively small, and very little energy waste is attributable to dirty ducts or equipment.

When to consider using a duct cleaner

The EPA suggests having air ducts cleaned only if there is visible evidence of specific problems:

  • Substantial mold growth (again, though, after identifying the source).
  • Infestation of insects or rodents.
  • Substantial deposits of dust or debris (if registers were not sealed during a renovation project, for example).

For specific health concerns, such as allergies or asthma, consult your physician first. The doctor may suggest other courses of action than duct cleaning. Bottom line: Your ducts are probably not the problem.

If you do hire a duct cleaner

Get several companies to come to your home to perform inspections and provide estimates. You may as well look for firms that belong to NADCA. Its members must subscribe to the NADCA code of ethics, must employ at least one NADCA-trained-and-certified technician, and are required to carry at least $500,000 in general liability insurance.

Also, check ratings for duct cleaners at Checkbook.org. We've arranged free access for Inquirer readers (see below).

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Delaware Valley Consumers' Checkbook magazine and Checkbook.org is a nonprofit organization with a mission to help consumers get the best service and lowest prices. We are supported by consumers and take no money from the service providers we evaluate. You can access all of Checkbook's ratings for free until Oct. 5 at Checkbook.org/Inquirer/Ducts.