Should You Have the
Air Ducts in Your Home Cleaned?
Table of Contents
Is Air Duct Cleaning?
Whether or Not to Have Your Air Ducts Cleaned
for Choosing a Duct Cleaning Service Provider
Expect of an Air Duct Cleaning Service Provider
How to Determine
if the Duct Cleaner Did a Thorough Job
How to Prevent Duct Contamination
Duct Cleaning Consumer Checklist
Issues of Duct Cleaning
To Learn More About Indoor
Most people are now aware that indoor air pollution is an issue
of growing concern and increased visibility. Many companies are marketing products
and services intended to improve the quality of your indoor air. You have probably
seen an advertisement, received a coupon in the mail, or been approached directly
by a company offering to clean your air ducts as a means of improving your home's
indoor air quality. These services typically but not always range in cost from
$450 to $1,000 per heating and cooling system, depending on the services offered,
the size of the system to be cleaned, system accessibility, climatic region,
and level of contamination.
Duct cleaning generally refers to the cleaning of various heating
and cooling system components of forced air systems, including the supply and
return air ducts and registers, grilles and diffusers, heat exchangers heating
and cooling coils, condensate drain pans (drip pans), fan motor and fan housing,
and the air handling unit housing (See diagram).
If not properly installed, maintained, and operated, these components
may become contaminated with particles of dust, pollen or other debris. If moisture
is present, the potential for microbiological growth (e.g., mold) is increased
and spores from such growth may be released into the home's living space. Some
of these contaminants may cause allergic reactions or other symptoms in people
if they are exposed to them. If you decide to have your heating and cooling
system cleaned, it is important to make sure the service provider agrees to
clean all components of the system and is qualified to do so. Failure to clean
a component of a contaminated system can result in re-contamination of the entire
system, thus negating any potential benefits. Methods of duct cleaning vary,
although standards have been established by industry associations concerned
with air duct cleaning. Typically, a service provider will use specialized tools
to dislodge dirt and other debris in ducts, then vacuum them out with a high-powered
In addition, the service provider may propose applying chemical
biocides, designed to kill microbiological contaminants, to the inside of the
ductwork and to other system components. Some service providers may also suggest
applying chemical treatments (sealants or other encapsulants) to seal or cover
the inside surfaces of the air ducts and equipment housings because they believe
the sealant will control mold growth or prevent the release of dirt particles
or fibers from ducts. These practices have yet to be fully researched and you
should be fully informed before deciding to permit the use of biocides or sealants
in your air ducts. They should only be applied, if at all, after the system
has been properly cleaned of all visible dust or debris.
Knowledge about the potential benefits and possible problems
of air duct cleaning is limited. Since conditions in every home are different,
it is impossible to generalize about whether or not air duct cleaning in your
home would be beneficial.
If no one in your household suffers from
allergies or unexplained symptoms or illnesses and if, after a visual inspection
of the inside of the ducts, you see no indication that your air ducts are contaminated
with large deposits of dust or mold (no musty odor or visible mold growth),
having your air ducts cleaned is probably unnecessary. It is normal for the
return registers to get dusty as dust-laden air is pulled through the grate.
This does not indicate that your air ducts are contaminated with heavy deposits
of dust or debris; the registers can be easily vacuumed or removed and cleaned.
On the other hand, if family members are experiencing unusual
or unexplained symptoms or illnesses that you think might be related to your
home environment, you should discuss the situation with your doctor. EPA has
published Indoor Air Quality: An Introduction for Health Professionals that
can be obtained free of charge by contacting IAQ INFO at the number listed in
this guide. You may obtain another free EPA booklet from IAQ INFO entitled The
Inside Story: A Guide to Indoor Air Quality for guidance on identifying possible
indoor air quality problems and ways to prevent or fix them.
You may consider having your air ducts cleaned simply because
it seems logical that air ducts will get dirty over time and should occasionally
be cleaned. While the debate about the value of periodic duct cleaning continues,
no evidence suggests that such cleaning would be detrimental, provided that
it is done properly.
On the other hand, if a service provider fails to follow proper
duct cleaning procedures, duct cleaning can cause indoor air problems. For example,
an inadequate vacuum collection system can release more dust, dirt, and other
contaminants than if you had left the ducts alone. A careless or inadequately
trained service provider can damage your ducts or heating and cooling system,
possibly increasing your heating and air conditioning costs or forcing you to
undertake difficult and costly repairs or replacements.
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should consider having the air ducts in your home cleaned if:
There is substantial visible mold growth inside hard surface
(e.g., sheet metal) ducts or on other components of your heating and cooling
system. There are several important points to understand concerning mold
detection in heating and cooling systems:
Many sections of your heating and cooling system may not
be accessible for a visible inspection, so ask the service provider to show
you any mold they say exists.
You should be aware that although a substance may look like
mold, a positive determination of whether it is mold or not can be made
only by an expert and may require laboratory analysis for final confirmation.
For about $50, some microbiology laboratories can tell you whether a sample
sent to them on a clear strip of sticky household tape is mold or simply
a substance that resembles it.
If you have insulated air ducts and the insulation gets
wet or moldy it cannot be effectively cleaned and should be removed and
replaced. If the conditions causing the mold growth in the first place are
not corrected, mold growth will recur.
Ducts are infested with vermin, e.g. (rodents or insects);
Ducts are clogged with excessive amounts of dust and debris
and/or particles are actually released into the home from your supply registers.
Other Important Considerations...
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 or go down after cleaning.
This is because much of the dirt that may accumulate inside air ducts adheres
to duct surfaces and does not necessarily enter the living space. It is important
to keep in mind that dirty air ducts are only one of many possible sources of
particles that are present in homes. Pollutants that enter the home both from
outdoors and indoor activities such as cooking, cleaning, smoking, or just moving
around can cause greater exposure to contaminants than dirty air ducts. Moreover,
there is no evidence that a light amount of household dust or other particulate
matter in air ducts poses any risk to health.
EPA does not recommend that air ducts be cleaned except on an
as-needed basis because of the continuing uncertainty about the benefits of
duct cleaning under most circumstances. If a service provider or advertiser
asserts that EPA recommends routine duct cleaning or makes claims about its
health benefits, you should notify EPA by writing to the address listed at the
end of this guidance. EPA does, however, recommend that if you have a fuel burning
furnace, stove, or fireplace, they be inspected for proper functioning and serviced
before each heating season to protect against carbon monoxide poisoning. Some
research also suggests that cleaning dirty cooling coils, fans and heat exchangers
can improve the efficiency of heating and cooling systems. However, little evidence
exists to indicate that simply cleaning the duct system will increase your system's
If you think duct cleaning might be a good idea for your home,
but you are not sure, talk to a professional. The company that services your
heating and cooling system may be a good source of advice. You may also want
to contact professional duct cleaning service providers and ask them about the
services they provide. Remember, they are trying to sell you a service, so ask
questions and insist on complete and knowledgeable answers.
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Do not assume that all duct cleaning service providers are equally
knowledgeable and responsible. Talk
to at least three different service providers and get written estimates before
deciding whether to have your ducts cleaned. When the service providers come
to your home, ask them to show you the contamination that would justify having
your ducts cleaned.
Do not hire duct cleaners who make sweeping claims about the
health benefits of duct cleaning such claims are unsubstantiated. Do not hire
duct cleaners who recommend duct cleaning as a routine part of your heating
and cooling system maintenance. You should also be wary of duct cleaners who
claim to be certified by EPA. EPA neither establishes duct cleaning standards
nor certifies, endorses, or approves duct cleaning companies.
Do not allow the use of chemical biocides or sealants unless
you fully understand the pros and the cons (See "Unresolved Issues of Duct
Check references to be sure other customers were satisfied and
did not experience any problems with their heating and cooling system after
Contact your county or city office of consumer affairs or local
Better Business Bureau to determine if complaints have been lodged against any
of the companies you are considering.
Interview potential service providers to ensure:
they are experienced in duct cleaning and have worked on
systems like yours;
they will use procedures to protect you, your pets, and
your home from contamination; and
they comply with NADCA's air duct cleaning standards and,
if your ducts are constructed of fiber glass duct board or insulated internally
with fiber glass duct liner, with the North American Insulation Manufacturers
Association's (NAIMA) recommendations.
If the service provider charges by the hour, request an estimate
of the number of hours or days the job will take, and find out whether there
will be interruptions in the work. Make sure the duct cleaner you choose will
provide a written agreement outlining the total cost and scope of the job before
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If you choose to have your ducts cleaned, the service provider should:
Open access ports or doors to allow the entire system to
be cleaned and inspected.
Inspect the system before cleaning to be sure that there
are no asbestos-containing materials (e.g., insulation, register boots,
etc.) in the heating and cooling system. Asbestos-containing materials require
specialized procedures and should not be disturbed or removed except by
specially trained and equipped contractors.
Use vacuum equipment that exhausts particles outside of
the home or use only high-efficiency particle air (HEPA) vacuuming equipment
if the vacuum exhausts inside the home.
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 internally lined with fiberglass. (Although flex duct
can also be cleaned using soft-bristled brushes, it can be more economical
to simply replace accessible flex duct.)
Take care to protect the ductwork, including sealing and
re-insulating any access holes the service provider may have made or used
so they are airtight.
Follow NADCA's standards for air duct cleaning and NAIMA's
recommended practice for ducts containing fiber glass lining or constructed
of fiber glass duct board.
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A thorough visual inspection is the best way to verify the cleanliness
of your heating and cooling system. Some service providers use remote photography
to document conditions inside ducts. All portions of the system should be visibly
clean; you should not be able to detect any debris with the naked eye. Show
the Post-Cleaning Consumer Checklist to the service provider before the work
begins. After completing the job, ask the service provider to show you each
component of your system to verify that the job was performed satisfactorily.
If you answer "No" to any of the questions on the
checklist, this may indicate a problem with the job. Ask your service provider
to correct any deficiencies until you can answer "yes" to all the
questions on the checklist.
Post-Cleaning Consumer Checklist:
Yes / No
- Did the service provider obtain access to and clean the entire
heating and cooling system, including ductwork and all components (drain pans,
humidifiers, coils, and fans)?
- Has the service provider adequately demonstrated that ductwork
and plenums are clean? (Plenum is a space in which supply or return air is
mixed or moves; can be duct, joist space, attic and crawl spaces, or wall
cavity.) - Heating
- Is the heat exchanger surface visibly clean? - Cooling Components
- Are both sides of the cooling coil visibly clean?
- If you point a flashlight into the cooling coil, does light
shine through the other side? It should if the coil is clean.
- Are the coil fins straight and evenly spaced (as opposed
to being bent over and smashed together)?
- Is the coil drain pan completely clean and draining properly?
- Are the blower blades clean and free of oil and debris?
- Is the blower compartment free of visible dust or debris?
- Is the return air plenum free of visible dust or debris?
- Do filters fit properly and are they the proper efficiency
as recommended by HVAC system manufacturer?
- Is the supply air plenum (directly downstream of the air
handling unit) free of moisture stains and contaminants? Metal Ducts
- Are interior ductwork surfaces free of visible debris? (Select
several sites at random in both the return and supply sides of the system.)
- Fiber Glass
- Is all fiber glass material in good condition (i.e., free
of tears and abrasions; well adhered to underlying materials)? - Access Doors
- Are newly installed access doors in sheet metal ducts attached
with more than just duct tape (e.g., screws, rivets, mastic, etc.)?
- With the system running, is air leakage through access doors
or covers very slight or non-existent? - Air Vents
- Have all registers, grilles, and diffusers been firmly reattached
to the walls, floors, and/or ceilings?
- Are the registers, grilles, and diffusers visibly clean?
Does the system function properly in both the heating and cooling
modes after cleaning?
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Whether or not you decide to have the air ducts in your home
cleaned, committing to a good preventive maintenance program is essential to
minimize duct contamination.
To prevent dirt from entering the system:
- Use the highest efficiency air filter recommended by the
manufacturer of your heating and cooling system.
- Change filters regularly.
- If your filters become clogged, change them more frequently.
- Be sure you do not have any missing filters and that air
cannot bypass filters through gaps around the filter holder.
- When having your heating and cooling system maintained or
checked for other reasons, be sure to ask the service provider to clean cooling
coils and drain pans.
- During construction or renovation work that produces dust
in your home, seal off supply and return registers and do not operate the
heating and cooling system until after cleaning up the dust.
- Remove dust and vacuum your home regularly. (Use a high efficiency
vacuum (HEPA) cleaner or the highest efficiency filter bags your vacuum cleaner
can take. Vacuuming can increase the amount of dust in the air during and
after vacuuming as well as in your ducts).
- If your heating system includes in-duct humidification equipment,
be sure to operate and maintain the humidifier strictly as recommended by
To prevent ducts from becoming wet:
Moisture should not be present in ducts. Controlling moisture
is the most effective way to prevent biological growth in air ducts.
- Moisture can enter the duct system through leaks or if the
system has been improperly installed or serviced. Research suggests that condensation
(which occurs when a surface temperature is lower than the dew point temperature
of the surrounding air) on or near cooling coils of air conditioning units
is a major factor in moisture contamination of the system. The presence of
condensation or high relative humidity is an important indicator of the potential
for mold growth on any type of duct. Controlling moisture can often be difficult,
but here are some steps you can take:
- Promptly and properly repair any leaks or water damage.
- Pay particular attention to cooling coils, which are designed
to remove water from the air and can be a major source of moisture contamination
of the system that can lead to mold growth. Make sure the condensate pan drains
properly. The presence of substantial standing water and/or debris indicates
a problem requiring immediate attention. Check any insulation near cooling
coils for wet spots.
- Make sure ducts are properly sealed and insulated in all
non-air-conditioned spaces (e.g., attics and crawl spaces). This will help
to prevent moisture due to condensation from entering the system and is important
to make the system work as intended. To prevent water condensation, the heating
and cooling system must be properly insulated.
- If you are replacing your air conditioning system, make sure
that the unit is the proper size for your needs and that all ducts are sealed
at the joints. A unit that is too big will cycle on an off frequently, resulting
in poor moisture removal, particularly in areas with high humidity. Also make
sure that your new system is designed to manage condensation effectively.
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Does duct cleaning prevent health problems?
The bottom line is: no one knows. There are examples of ducts
that have become badly contaminated with a variety of materials that may pose
risks to your health. The duct system can serve as a means to distribute these
contaminants throughout a home. In these cases, duct cleaning may make sense.
However, a light amount of household dust in your air ducts is normal. Duct
cleaning is not considered to be a necessary part of yearly maintenance of your
heating and cooling system, which consists of regular cleaning of drain pans
and heating and cooling coils, regular filter changes and yearly inspections
of heating equipment. Research continues in an effort to evaluate the potential
benefits of air duct cleaning.
In the meantime educate yourself about duct cleaning by contacting
some or all of the sources of information listed at the end of this publication
and asking questions of potential service providers.
Are duct materials other than bare sheet metal
ducts more likely to be contaminated with mold and other biological contaminants?
You may be familiar with air ducts that are constructed of sheet
metal. However, many modern residential air duct systems are constructed of
fiber glass duct board or sheet metal ducts that are lined on the inside with
fiber glass duct liner. Since the early 1970's, a significant increase in the
use of flexible duct, which generally is internally lined with plastic or some
other type of material, has occurred. The use of insulated duct material has
increased due to improved temperature control, energy conservation, and reduced
condensation. Internal insulation provides better acoustical (noise) control.
Flexible duct is very low cost. These products are engineered specifically for
use in ducts or as ducts themselves, and are tested in accordance with standards
established by Underwriters Laboratories (UL), the American Society for Testing
and Materials (ASTM), and the National Fire Protection Association (NFPA).
Many insulated duct systems have operated for years without
supporting significant mold growth. Keeping them reasonably clean and dry is
generally adequate. However, there is substantial debate about whether porous
insulation materials (e.g., fiber glass) are more prone to microbial contamination
than bare sheet metal ducts. If enough dirt and moisture are permitted to enter
the duct system, there may be no significant difference in the rate or extent
of microbial growth in internally lined or bare sheet metal ducts. However,
treatment of mold contamination on bare sheet metal is much easier. Cleaning
and treatment with an EPA-registered biocide are possible. Once fiberglass duct
liner is contaminated with mold, cleaning is not sufficient to prevent regrowth
and there are no EPA-registered biocides for the treatment of porous duct materials.
EPA, NADCA, and NAIMA all recommend the replacement of wet or moldy fiber glass
In the meantime experts do agree that moisture should not be
present in ducts and if moisture and dirt are present, the potential exists
for biological contaminants to grow and be distributed throughout the home.
Controlling moisture is the most effective way to prevent biological growth
in all types of air ducts.
- Correct any water leaks or standing water.
- Remove standing water under cooling coils of air handling
units by making sure that drain pans slope toward the drain.
- If humidifiers are used, they must be properly maintained.
- Air handling units should be constructed so that maintenance
personnel have easy, direct access to heat exchange components and drain pans
for proper cleaning and maintenance.
- Fiber glass, or any other insulation material that is wet
or visibly moldy (or if an unacceptable odor is present) should be removed
and replaced by a qualified heating and cooling system contractor.
- Steam cleaning and other methods involving moisture should
not be used on any kind of ductwork.
Air duct cleaning service providers may tell you that they need
to apply a chemical biocide to the inside of your ducts to kill bacteria (germs),
and fungi (mold) and prevent future biological growth. Some duct cleaning service
providers may propose to introduce ozone to kill biological contaminants. Ozone
is a highly reactive gas that is regulated in the outside air as a lung irritant.
However, there remains considerable controversy over the necessity and wisdom
of introducing chemical biocides or ozone into the ductwork.
Among the possible problems with biocide and ozone application
in air ducts:
Little research has been conducted to demonstrate the effectiveness
of most biocides and ozone when used inside ducts. Simply spraying or otherwise
introducing these materials into the operating duct system may cause much
of the material to be transported through the system and released into other
areas of your home.
Some people may react negatively to the biocide or ozone,
causing adverse health reactions.
Chemical biocides are regulated by EPA under Federal pesticide
law. A product must be registered by EPA for a specific use before it can be
legally used for that purpose. The specific use(s) must appear on the pesticide
(e.g., biocide) label, along with other important information. It is a violation
of federal law to use a pesticide product in any manner inconsistent with the
A small number of products are currently registered by EPA specifically
for use on the inside of bare sheet metal air ducts. A number of products are
also registered for use as sanitizers on hard surfaces, which could include
the interior of bare sheet metal ducts. While many such products may be used
legally inside of unlined ducts if all label directions are followed, some of
the directions on the label may be inappropriate for use in ducts. For example,
if the directions indicate "rinse with water", the added moisture
could stimulate mold growth.
All of the products discussed above are registered solely for
the purpose of sanitizing the smooth surfaces of unlined (bare) sheet metal
ducts. No products are currently registered as biocides for use on fiber glass
duct board or fiber glass lined ducts, so it is important to determine if sections
of your system contain these materials before permitting the application of
In the meantime before allowing a service provider to use a
chemical biocide in your ductwork, the service provider should:
Demonstrate visible evidence of microbial growth in your
ductwork. Some service providers may attempt to convince you that your air
ducts are contaminated by demonstrating that the microorganisms found in
your home grow on a settling plate (i.e., petri dish). This is inappropriate.
Some microorganisms are always present in the air, and some growth on a
settling plate is normal. As noted earlier, only an expert can positively
identify a substance as biological growth and lab analysis may be required
for final confirmation. Other testing methods are not reliable.
Explain why biological growth cannot be removed by physical
means, such as brushing, and further growth prevented by controlling moisture.
If you decide to permit the use of a biocide, the service
Show you the biocide label, which will describe its range
of approved uses.
Apply the biocide only to un-insulated areas of the duct
system after proper cleaning, if necessary to reduce the chances for re-growth
Always use the product strictly according to its label instructions.
While some low toxicity products may be legally applied while
occupants of the home are present, you may wish to consider leaving the premises
while the biocide is being applied as an added precaution.
Do sealants prevent the release of dust and dirt
particles into the air?
Manufacturers of products marketed to coat and seal duct surfaces
claim that these sealants prevent dust and dirt particles inside air ducts from
being released into the air. As with biocides, a sealant is often applied by
spraying it into the operating duct system. Laboratory tests indicate that materials
introduced in this manner tend not to completely coat the duct surface. Application
of sealants may also affect the acoustical (noise) and fire retarding characteristics
of fiber glass lined or constructed ducts and may invalidate the manufacturer's
Questions about the safety, effectiveness and overall desirability
of sealants remain. For example, little is known about the potential toxicity
of these products under typical use conditions or in the event they catch fire.
In addition, sealants have yet to be evaluated for their resistance
to deterioration over time which could add particles to the duct air.
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- Learn as much as possible about air duct cleaning before
you decide to have your ducts cleaned by reading this guidance and contacting
the sources of information provided.
- Consider other possible sources of indoor air pollution first
if you suspect an indoor air quality problem exists in your home.
- Have your air ducts cleaned if they are visibly contaminated
with substantial mold growth, pests or vermin, or are clogged with substantial
deposits of dust or debris.
- Ask the service provider to show you any mold or other biological
contamination they say exists. Get laboratory confirmation of mold growth
or decide to rely on your own judgment and common sense in evaluating apparent
- Check references.
- Insist that the service provider give you knowledgeable and
complete answers to your questions.
- Find out whether your ducts are made of sheet metal, flex
duct, or constructed of fiber glass duct board or lined with fiber glass since
the methods of cleaning vary depending on duct type. Remember, a combination
of these elements may be present.
- Permit the application of biocides in your ducts only if
necessary to control mold growth and only after assuring yourself that the
product will be applied strictly according to label directions. As a precaution,
you and your pets should leave the premises during application.
- Do not permit the use of sealants except under unusual circumstances
where other alternatives are not feasible.
- Commit to a preventive maintenance program of yearly inspections
of your heating and cooling system, regular filter changes, and steps to prevent
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- U.S. Environmental Protection Agency Office of Radiation
and Indoor Air Indoor Environments Division (6604J) 401 M St., S.W. Washington,
DC 20460 (202) 564-9370 (202) 565-2038 (fax) E-mail: firstname.lastname@example.org
World Wide Web Site: http://www.epa.gov/iaq/
- Indoor Air Quality Information Clearinghouse (IAQ INFO) P.O.
Box 37133 Washington, DC 20013-7133 1 (800) 438-4318 (202) 484-1307 E-mail:
- Useful EPA publications available free of charge from either
- The Inside Story: A Guide to Indoor Air Quality Indoor Air
Pollution: An Introduction for Health Professionals Residential Air Cleaning
Devices: A Summary of Available Information
- Consumer Research Council (CRC) IAQ Checklist P.O. Box 12099
Washington, DC 20005-0999
- Ask for: How Healthy Is The Air In Your Home? (Free. Send
a self-addressed, stamped standard size business envelope)
To Learn More About Air Duct Cleaning
- National Air Duct Cleaners Association (NADCA) 1518 K Street,
NW Suite 503 Washington, DC 20005 (202) 737-2926 http://www.nadca.com Ask
for: Introduction to HVAC (Heating, Ventilating, and Air Conditioning) System
Cleaning Services (Although intended for commercial customers, information
can be useful to consumers.)
- North American Insulation Manufacturers Association (NAIMA)
44 Canal Center Plaza, Suite 310 Alexandria, VA 22314 (703) 684-0084 Ask for:
Cleaning Fibrous Glass Insulated Air Duct Systems; Recommended Practice
Other Useful Resources
- For a free list of state and local consumer protection agencies
and Better Business Bureaus:
- Consumer's Resource Handbook Consumer Information Center
Pueblo, CO 81009
- For Information on Antimicrobial Biocides:
National Antimicrobial Information Network (NAIN) 1 (800) 447-6349