Air Duct Cleaning

From EPA.GOV: 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, and then vacuum them out with a high-powered vacuum cleaner.
If you decide to have your heating and cooling system cleaned, it important to make sure the service provider agrees to clean all components of the system and is qualified to do so.

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.
• Ducts are infested with vermin (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.