Last updated November 2018
Do ducts get dirty? Sure they do!
Should you have them cleaned?
Then why do so many companies recommend this service?
Because they’re wrong or get paid to clean ducts.
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 language like, “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.
What They Do
To clean ductwork, companies place the duct system under negative pressure—essentially connecting a very large, powerful vacuum cleaner to one or more openings in the ductwork and sucking out loose dust and other debris. Because a vacuum isn’t powerful enough to loosen and remove all particles, duct cleaners must agitate the dust inside the ducts using a rotary brush, compressed air nozzles, and a special tool called a “skipper ball.” Duct-cleaning companies may also clean the heating and cooling equipment (heat exchangers, cooling coils, condensate drain pans, fan motors, fan blades, and fan housings), but cleaning this equipment isn’t always included in a duct-cleaning company’s basic service.
Why It’s Unnecessary
Although duct-cleaning operations may insist that duct cleaning is essential for your health, the evidence does not support their claims. While it intuitively makes sense to clean ductwork—after all, you dust and clean the rest of your house, so why not clean your ducts?—the fact is dust that settles in your ventilation system generally stays where it is, unlikely to become airborne unless disturbed. Under most circumstances, it is inert and harmless, and stirring it up with cleaning equipment actually creates bigger problems.
Little research has been done on the effects of duct cleaning. U.S.- and Canadian-government studies and health professionals who have investigated duct cleaning stop short of recommending against it, but neither do they endorse it as a routine measure.
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) 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 no significant improvement in air quality, and found 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:
Although duct cleaning done by a professional duct cleaner will remove dust and debris… 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 different 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 that 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 are the same.
The American Lung Association’s position on duct cleaning affirms the EPA’s statement and recommendations, but adds:
When health problems are believed to be the result of biological contaminants or dust in indoor air, it is important to first determine that contaminated ducts are the cause of the health problems and verify that the ducts are, in fact, contaminated. The source of the problem may lie elsewhere, so cleaning ducts may not permanently solve the problem.
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. 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.
Duct Cleaning 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.”
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.
CMHC duct-cleaning study 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 that dirt doesn’t build up and get drawn into the system. It also prevents water, which can cause mold problems, from accumulating on and beneath the coils.
Also consider having your duct system inspected for leaks, since 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. We have ratings of duct-cleaning outfits here at Checkbook.org, but 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.
Cleaners Might Damage Your Ducts and Home
While there’s little reason to hire a duct cleaner, here’s one more reason to avoid them: Performed improperly, duct cleaning can do more harm than good.
If the vacuum pressure isn’t applied carefully, some of the dust that settled in the ducts will be loosened by the agitation and blown into the living space after the cleaning. (This explains the results of the Canadian study in which particle levels actually rose immediately after a cleaning.)
Running brushes or using compressed air also risks breaking seals in the duct system, which can be especially problematic in the return-air portion. Most forced-air systems are designed as closed loops, and leaks in the return-air circuit allow unfiltered air to be sucked from basements or attics, bringing with it dust and moisture.
Not every home contains sheet-metal ductwork. Flexible coil-style ducts—the kind that looks like a Slinky toy—are more vulnerable to being punctured.
Ductwork fabricated from fiberglass-insulated material—which is less expensive than metal ductwork—has become more common in new homes. These ducts have fiberglass insulation on their interior surfaces. The fiberglass surface is sealed, but if a duct-cleaning company is not careful, the cleaning can damage the insulation, loosening fibers that can become airborne.
And, of course, there are the usual types of problems that can occur when you deal with any contractor—evidenced by the negative customer reviews some companies receive at Checkbook.org.
Problems That Warrant a Cleaning
In general, consider duct cleaning only in response to specific identifiable problems. For example, the EPA suggests having air ducts cleaned only if there is visible evidence of:
- Substantial mold growth (but see below)
- 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 alternative courses of action 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 Have Special Concerns 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 always 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. Better to track down and eliminate moisture problems—whether under a sink or part of a heating and cooling system.
Still Going to Hire One? What to Look for and Avoid
If you decide to have your ducts cleaned anyway, don’t hire a company that makes sweeping claims about health benefits or that it’s “EPA-certified” for duct cleaning: That agency offers no such certification.
You’ll find customer reviews of duct-cleaning outfits here at Checkbook.org. We also evaluate HVAC services, which are really better bets if you want to have your equipment serviced and cleaned.
Among duct-cleaning operations, focus your search on contractors that belong to the National Air Duct Cleaners Association (NADCA), a trade association. Its bar to qualify for membership is somewhat low: There’s a code of ethics and member companies must employ at least one NADCA-trained-and-certified technician and promise to use NADCA-approved methods. Members must also carry at least $500,000 in general liability insurance.
Shop for a good price. Checkbook’s undercover shoppers collected price quotes from a handful of local companies for a straightforward duct-cleaning job, including equipment cleaning, and found huge company-to-company price differences among bids based on identical specifications. Quotes for our sample home ranged from less than $300 to more than $650. With some companies, cleaning the equipment was part of the deal—they did it whether you wanted it or not. Other companies impose an extra charge for equipment cleaning.
Beware of companies that quote very low prices (under $200) for duct-cleaning work. Some use low “starting” prices as a bait-and-switch tactic; others do very little to earn it.
If you’re worried about specific contaminants (mold, dust), ask companies to inspect the job beforehand. Ask them to show you any contamination that would justify having your ducts cleaned. Be very skeptical if a company issues dire warnings about the presence of mold, which is usually not found in ductwork. If they suspect mold, ask them to submit the sample to a lab for analysis.
Another mega red flag: companies that propose applying biocides—agents that kill microorganisms. The EPA cautions against these chemicals. While some are approved for duct cleaning, the chemicals themselves can be irritants. If you choose to have a biocide applied as part of a duct cleaning, ask the company to present evidence that the chemical has been approved for use in duct-cleaning applications (it should have the EPA data sheet for the chemical on hand). Note: Biocides and other chemicals should never be applied to fiberglass-lined ductwork.
Confirm that any cleaning will cover the entire system. A cleaning should include supply ductwork, return ductwork, supply plenum (chamber), return plenum, and all registers and grilles. You may agree, for a reduced price, to exclude the blower-fan assembly, heat exchangers, evaporator coils, and collector pans if those are serviced under a maintenance plan with a heating and air-conditioning contractor. But these are the elements most relevant to system efficiency and should be explicitly listed by the duct-cleaning company, unless you have agreed to exclude them.
Before agreeing to any work, get written estimates after each inspection.
Get the company to agree in writing that it will perform the following (which mostly follow EPA recommendations):
- Open or create access ports or doors to allow the entire system to be cleaned and inspected.
- Inspect the system before cleaning to make sure there are no asbestos-containing materials (e.g., insulation, register boots, etc.) in the heating and cooling system. (Asbestos-containing materials should be disturbed or removed only by specially trained and equipped contractors.)
- Follow NADCA guidelines in attaching some sort of vacuum device to the system during cleaning to remove loosened particles. (NADCA does not endorse any one type of equipment. Truck-mounted equipment is typically more powerful and ensures that loosened particles are sucked outside the home. Portable equipment can be located nearer the work site.)
- Use vacuum equipment that exhausts particles outside of the home or, if the vacuum exhausts inside the home, use only vacuuming equipment with high-efficiency particulate air (HEPA) filters.
- Protect carpet and household furnishings during cleaning.
- Use well-controlled brushing of duct surfaces in conjunction with contact vacuum cleaning to dislodge dust and other particles.
- Use only soft-bristled brushes for fiberglass duct board and sheet metal ducts lined internally with fiberglass. (Although flex duct can also be cleaned using soft-bristled brushes, it can be more economical to replace accessible flex duct.)
- Take care to protect the ductwork, including sealing and reinsulating any access holes that have been made or used.
- Follow NADCA standards for air-duct cleaning and North American Insulation Manufacturers Association recommended practices for ducts containing fiberglass lining or constructed of fiberglass duct board.