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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, cleaning your ducts 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.

Although duct-cleaning operations may insist duct cleaning is essential for your health, the evidence does not support their claims. Companies that perform duct cleaning often advertise health benefits or suggest duct cleaning will lower your power bills by improving your system’s efficiency. Some ads even use language like, “Studies have shown . . . ” but no data back up these claims. Even if your ducts are dirty, cleaning them probably 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.

Although it intuitively makes sense to clean ductwork — after all, you dust and clean the rest of your house — the fact is dust that settles in your ventilation system generally stays where it is, unlikely to become airborne unless disturbed. Under most circumstances, the dust is inert and harmless, and stirring it up with cleaning equipment actually creates bigger issues.

Little research has been done on the effects of duct cleaning. Government studies from the United States and Canada and health professionals who have investigated duct cleaning stop short of recommending against it, but they also don’t endorse it as a routine measure.

A study done by U.S. Environmental Protection Agency researchers measured dust levels and HVAC system efficiency in test homes during a one-week period during the cooling season and found duct cleaning did not significantly improve dust levels or system performance. Based on that report and other independent research, the EPA’s official advisory on duct cleaning 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 Canada Mortgage and Housing Corporation (CMHC), a government agency, conducted a study in the 1990s to investigate two claims: Duct cleaning makes indoor air healthier; and it reduces energy costs by improving airflow. After testing 33 homes in Montreal before and after duct cleaning, the study found that there was 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.

Like the EPA, the CMHC concluded that duct cleaning is unnecessary:

“Ideally, the inside surface will be shiny and bright after cleaning. Duct cleaning may be justifiable to you personally for that very reason: you may not want to have your house air circulated through a duct passage that is not as clean as the rest of the house. However, duct cleaning will not usually change the quality of the air you breathe, nor will it significantly affect airflows or heating costs.”

The EPA and CMHC researchers used different methodologies. The CMHC study called on several duct-cleaning services. The companies were not made aware they were part of a study, and the researchers did not control for time spent or methods used. The EPA study prescribed and controlled methods used on a smaller number of homes. While the duct-cleaning industry argues both studies have flaws, no other research has challenged the findings. And although the equipment and methods used by duct-cleaning companies have changed since these studies were conducted, the air ducts in homes haven’t.

Regularly change your filter

Frequently changing air filters is the best way to keep dust, allergens and other particles out of your home. With a newly installed system, or a system in a home you’ve just moved into, check your filter monthly to determine how quickly it gets dirty at different times of the year. Most should be replaced every two or three months.

It won't save energy, either

Although not always part of their basic cleaning services, many duct-cleaning companies often also clean the heating and cooling equipment (heat exchangers, cooling coils, condensate drain pans, fan motors, fan blades and fan housings).

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 because of 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 little energy waste is attributable to dirty ducts or equipment.

CMHC researchers found that when duct cleaners also cleaned the blower-fan blades, there was a small reduction in airborne particles. Cleaning the blower fan might also slightly improve your system’s energy efficiency.

The same holds true for the evaporator coils inside your home’s cooling system. Evaporator coils cause condensation, dehumidifying the air before it circulates through your home. Condensed moisture can cause dust and other particles to stick to and build up on the coils. Also, cleaning the collector pan (and the drain spout in the pan) beneath the coils ensures dirt doesn’t build up and get drawn into the system. It also prevents water from accumulating on and beneath the coils, which can cause mold problems.

Also consider having your duct system inspected for leaks, because leaky ducts lower efficiency and introduce air-quality problems.

But we don’t recommend hiring a duct cleaner to perform these tasks; too many don’t really know what they’re doing, according to the ratings of duct-cleaning outfits we have collected from local consumers. Consider hiring a top-notch heating and air-conditioning contractor to do this type of work, or pay them to do it during their next service visit. Readers can access Checkbook’s HVAC company ratings through Feb. 28 at Checkbook.org/washingtonpost/ducts.

Issues that warrant cleaning

In general, consider duct cleaning only in response to specific identifiable problems. For example, the EPA suggests having air ducts cleaned if there is visible evidence of:

•Substantial mold growth.

•Infestation of insects or rodents.

•Substantial deposits of dust or debris (if registers were not sealed during a renovation project, for example).

If anyone in your household has specific health concerns, such as allergies or asthma, consult your physician first. It’s important to identify the problem so your doctor can suggest alternatives to duct cleaning. Start by identifying whether your ducts are part of the problem (they probably aren’t) and whether getting them cleaned will help (it probably won’t).

If you're worried about mold

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 begins with a moisture problem, and the ducts themselves are unlikely to be the source. 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. Again, if you suspect a mold problem, consider having a service company inspect the duct system for leaks.

If you suspect — but aren’t sure — that what you see is mold, you might be tempted to have it tested. But experts we consulted generally recommend against it, reasoning that:

•Mold is present in all homes; it becomes problematic only when there is a moisture problem.

•It’s generally not worth the cost to test for mold or to identify the different kinds of mold present. It’s better to track down and eliminate moisture problems — whether under a sink or part of a heating and cooling system.

Washington 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 Checkbook’s ratings of local HVAC companies free of charge until Feb. 28 at Checkbook.org/washingtonpost/ducts.