Heating, ventilation, and air conditioning (HVAC) systems have been shown to act as a collection source for various contaminants that have the potential to affect your health, such as mold, fungi, bacteria and dust. Cleaning your air ducts should be considered one component in an overall plan to improve your indoor air quality.
Research has also demonstrated that having your HVAC system cleaned can allow it to run more efficiently by removing debris from sensitive mechanical components. Clean, efficient systems are less likely to break down, have a longer life span, and generally operate more efficiently than dirty systems.
How often you have your air ducts cleaned depends on several factors, which includes your personal preference. Some of the things that may lead a home owner to consider more frequent cleaning are:
Smokers in the household
Pets that shed a lot
Water contamination from a flood, or excessive moisture from condensation
If you have allergies or asthma and would benefit from a reduction in the amount of indoor pollutants in your home’s HVAC system
After home renovations or remodeling
Prior to moving to a new home
If there is substantial visible mold growth in your ducts
If your ducts have been infested with mice or insects
Or if your ducts are clogged with excessive amounts of dust and debris, and particles are actually being released into the home from your registers.
Source: www.nadca.com/consumerinformation/residentialconsumer.aspx, and www.epa.gov