According to the Environmental Protection Agency, 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.

The EPA says if not properly installed, maintained, and operated, components of forced air systems may become contaminated with particles of dust, pollen or other debris. When moisture is present, the potential for microbiological growth, mold, increases 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

The EPA claims that no evidence suggests that such cleaning would be detrimental, provided that it is done properly. One may consider having their air ducts cleaned simply because it seems logical that air ducts will get dirty over time, and should occasionally be cleaned.

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 also 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.

• Presence of mold growth inside sheet metal ducts or on other components of the heating and cooling system. 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.

Many companies have begun marketing products and services for use in the home to improve the quality of the indoor air. Duct cleaning is one such service. The EPA says that 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.