Summary

Knowledge about air duct cleaning is in its early stages, so a blanket recommendation cannot be offered as to whether you should have your air ducts in your home cleaned.  The U.S. Environmental Protection Agency (EPA) urges you to read this document in it entirety as it provides important information on the subject.

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.  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 mater in air ducts poses any risk to your health.

You 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); or
	Ducts are clogged with excessive amounts of dust and debris and/or particles are actually released into the home from your supply registers.

If any of the conditions identified above exists, it usually suggests one or more underlying causes.  Prior to any cleaning, retrofitting, or replacing of your ducts, the cause or causes must be corrected or else the problem will likely recur.

Some research suggests that cleaning heating and cooling system components (e.g., cooling coils, fans and heat exchangers) may improve the efficiency of your system, resulting in a longer operating life, as well as some energy and maintenance cost savings.  However, little evidence exists that cleaning only the ducts will improve the efficiency of the system. 

You may consider having your air ducts cleaned simply because it seems logical that air ducts will get dirty over time and should be occasionally cleaned.  Provided that the cleaning is done properly, no evidence suggests that such cleaning would be detrimental.  EPA does not recommend that the air ducts be cleaned routinely, but only as needed.  If a service provider or advertiser asserts that EPA recommends routine duct cleaning or makes claims about its health benefits, you should write EPA.  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.

If you do decide to have your air ducts cleaned, take the same consumer precautions you normally would in assessing the service provider's competence and reliability.

Air duct cleaning service providers may tell you that they need to apply chemical biocide to the inside of your ducts as a means to kill bacteria (germs) and fungi (mold) and prevent future biological growth.  They may also propose the application of a "sealant" to prevent dust and dirt particles from being released into the air or to seal air leaks.  You should fully understand the pros and cons of permitting application of chemical biocides or sealants.  While the targeted use of chemical biocides and sealants may be appropriate under specific circumstances, research has not demonstrated their effectiveness in duct cleaning or their potential adverse health effects.  No chemical biocides are currently registered by EPA for use in internally-insulated air duct systems (see Should chemical biocides be applied to the inside of air ducts?).

Whether or not you decide to have the air ducts in your home cleaned, preventing water and dirt from entering the system is the most effective way to prevent contamination (see How to Prevent Duct Contamination).

What is Air Duct Cleaning?

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 encapsulate or cover the inside surfaces of the air ducts and equipment housings because they believe it 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 chemical treatments 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.

Note:  Use of sealants to encapsulate the inside surfaces of ducts is a different practice than sealing duct air leaks.  Sealing duct air leaks can help save energy on heating and cooling bills.  For more information, see EPA's www.energystar.gov/ducts 

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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.

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 and 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.

You 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); 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...

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 efficiency.

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.

Suggestions for Choosing a Duct Cleaning Service Provider

To find companies that provide duct cleaning services, check your Yellow Pages under "duct cleaning" or contact the National Air Duct Cleaners Association (NADCA) at the address and phone number in the information section located at the end of this guidance. 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 chemical treatments unless you fully understand the pros and the cons
	Check references to be sure other customers were satisfied and did not experience any problems with their heating and cooling system after cleaning.
	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.
	Ask the service provider whether they hold any relevant state licenses. As of 1996, the following states require air duct cleaners to hold special licenses: Arizona, Arkansas, California, Florida, Georgia, Michigan and Texas. Other states may require them as well.
	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 work begins.

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What to Expect From an Air Duct Cleaning Service Provider

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 duct work, 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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