Heating Care and Repair
What Is Air Duct
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.
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 vacuum cleaner.
In addition, the
service provider may propose applying chemical biocides, designed to
kill microbiological contaminants, to the inside of the duct work 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.
Deciding Whether or Not to Have Your
Air Ducts Cleaned
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.
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.
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.
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.
should consider having the air ducts in your home cleaned if:
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
• 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); or 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
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
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.
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
How to Determine if
the Duct Cleaner Did A Thorough Job
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.
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
Post-Cleaning Consumer Checklist
service provider obtain access to and clean the entire
heating and cooling system, including ductwork and all
components (drain pans, humidifiers, coils, and fans)?
service provider adequately demonstrated that duct work
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.)
Is the heat
exchanger surface visibly clean?
both sides of the cooling coil visibly clean?
point a flashlight into the cooling coil, does light shine
through the other side? It should if the coil is clean.
coil fins straight and evenly spaced (as opposed to being
bent over and smashed together)?
coil drain pan completely clean and draining properly?
blower blades clean and free of oil and debris?
blower compartment free of visible dust or debris?
return air plenum free of visible dust or debris?
filters fit properly and are they the proper efficiency as
recommended by HVAC system manufacturer?
supply air plenum (directly downstream of the air handling
unit) free of moisture stains and contaminants?
interior ductwork surfaces free of visible debris? (Select
several sites at random in both the return and supply sides of
fiber glass material in good condition (i.e., free of tears
and abrasions; well adhered to underlying materials)?
newly installed access doors in sheet metal ducts attached
with more than just duct tape (e.g., screws, rivets,
the system running, is air leakage through access doors or
covers very slight or non-existent?
all registers, grilles, and diffusers been firmly
reattached to the walls, floors, and/or ceilings?
registers, grilles, and diffusers visibly clean?
system function properly in both the heating and cooling modes
BACK TO TOP
How to Prevent
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.
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.
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.
construction or renovation work that produces dust in your home, seal
off supply and return registersand do not operate the heating and
cooling system until after cleaning up the dust.
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).
your heating system includes in-duct humidification equipment, be sure
to operate and maintain the humidifier strictly as recommended by the
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:
and properly repair any leaks or water damage.
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.
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.
Does duct cleaning
prevent health problems?
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...
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?
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
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).
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.
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 re-growth 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 duct material.
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
Correct any water
leaks or standing water.
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
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
biocides be applied to the inside of air ducts?
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 duct work.
Among the possible
problems with biocide and ozone application in air ducts:
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.
people may react negatively to the biocide or ozone, causing adverse
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 user(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 label directions.
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 any biocide.
In the meantime...
Before allowing a
service provider to use a chemical biocide in your duct work, the
service provider should:
visible evidence of microbial growth in your duct work.
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 provider
Show you the biocide label, which will describe its range of approved
Apply the biocide only to un-insulated areas of the duct system after
proper cleaning, if necessary to reduce the chances for re-growth of
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?
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.
sealants have yet to be evaluated for their resistance to
deterioration over time which could add particles to the duct air.
Fans Solve Bathroom Moisture Woes
One of the most
important fixtures in the bathroom is also one of the least expensive
and least noticeable - the ventilation fan. Mounted in the ceiling or
in the wall, ventilation fans help rid the bathroom of odors and, more
importantly, of potentially damaging moisture.
There are really
four things you need to be concerned about in the selection and
installation of a bathroom ventilation fan - air movement capacity,
noise level, ducting and optional accessories. Each plays an important
role in the fan's proper operation
In the meantime...
concerned with duct cleaning, including EPA, NADCA, NAIMA, and the
Sheet Metal and Air Conditioning Contractors' National Association (SMACNA)
do not currently recommend the routine use of sealants in any type of
duct. Instances when the use of sealants may be appropriate include
the repair of damaged fiber glass insulation or when combating fire
damage within ducts. Sealants should never be used on wet duct liner,
to cover actively growing mold, or to cover debris in the ducts, and
should only be applied after cleaning according to NADCA or other
appropriate guidelines or standards.
your ducts for air leaks. First look for sections that should be
joined but have separated and then look for obvious holes.
you use duct tape to repair and seal your ducts, look for tape with
the Underwriters Laboratories (UL) logo to avoid tape that degrades,
cracks, and loses its bond with age.
Remember that insulating ducts in the basement will make the basement
colder. If both the ducts and the basement walls are uninsulated,
consider insulating the basement walls and the ducts.
your basement has been converted to a living area, install both supply
and return registers in the basement rooms.
sure a well-sealed vapor barrier exists on the outside of the
insulation on cooling ducts to prevent moisture buildup.
professional to help you insulate and repair all ducts.
How to Repair and
Seal Heating & Cooling Air Ducts
Unsealed or poorly
sealed ducts can be one of the biggest energy and money losers in a
home. Remember: insulation wrapped around ducts does not stop air
How to Seal Air
Ducts with Mastic
Mastic seals better
and lasts longer than tape. For an experienced installer, mastic is
faster to apply than tape.
A. Clean Duct
Use a cloth to wipe dust from the surface of the duct. If oily film or
grease covers the duct, wipe clean with a damp cloth.
B. Joints with Less
than 1/4 Inch Gaps. Load brush with mastic. Coat the entire joint with a
continuous strip of mastic. Use end of the brush to work mastic into
joint. Spread mastic at least one inch on each side of the joint.
Mastic should be thick enough to hide the metal surface of duct --
about 1/16 inch thick.
C. Joints with Gaps
Greater Than 1/4 Inch. If the gap in the duct connection is larger than 1/4 inch
use fiberglass reinforcing membrane in addition to mastic. If the
membrane is sticky on one side, cut enough membrane to cover the
joint, press the membrane in place, then cover with mastic. Apply
enough mastic to completely cover the membrane. If the membrane does
not have a sticky side, first apply a thin layer of mastic, press the
membrane into the mastic, then apply the finish layer of mastic.
D. Wrap Ducts with
Insulation. RCD Masticsdry to touch in 2 to 4 hours. Insulation can be installed
over wet mastic. But try not to move the ducts too much, because the
mastic seal could be damaged. All duct support work should be done
before applying mastic.
reinforcing membrane wrinkles when it's run along a joint between
round and rectangular ducts. Here's how to make it lie flat. With a
utility knife, make a series of slices about every two inches. When
wrapped around the round duct the slices will fan out like a "hoola
When a Caulking Gun
mastic with a brush does not provide good control over the mastic
applied. Where appearance and wasted mastic are a concern, a caulking
gun works best. See diagrams below to learn where to seal.
Use a UL 181A-M and
UL 181 B-M Listed mastic designed for the type of duct being installed
or repaired. Mastic can be applied by gloved hand, brush, trowel or
caulking gun. Insulation can be installed over mastic that is still
This product is
designed to be used with mastics. It reinforces the mastic when there
is a gap of 1/4 inch or more. If the membrane has a sticky side, apply
it over the cleaned metal surface, then apply the mastic. If the
membrane does not have a sticky side, first apply a thin layer of
mastic, then place the membrane in this layer of mastic and add
another layer of mastic over the top so the membrane is completely
Flexible ducts can
easily be pinched by wire or twine supports so air flow is restricted.
The best support material is woven polypropylene strap that comes in
various widths. Sometimes called "webbing strap," this material is
wide enough so it won't bite into flex duct. For convenience, use it
for both metal and flex duct support.
Tools & Supplies
Content provided by RCD Corporation
Books: Should You Have the Air Ducts in Your Home Cleaned?