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 show 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 matter stages in air ducts poses any risk to your health.
You should consider having the air ducts stages in your home clean if:
checkmark 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 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 clean and should remove and replaced.
If the conditions causing the mold growth in the first place are not correct, mold stages growth will recur.
checkmark Ducts are infest with vermin, e.g. (rodents or insects).
checkmark Ducts are clog with excessive amounts of dust and debris and/or particles are actually release 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 correct or else the problem will likely recur.