The duct system in your home is the vehicle through which your heated and cooled air is distributed throughout your home.  Moisture should never be present in ducts. Controlling moisture is the most effective way to prevent biological growth in air ducts.

Moisture can enter the duct system through leaks or if the system has been improperly installed or serviced. Research suggests that condensation (which occurs when a surface temperature is lower than the dew point temperature of the surrounding air) on or near cooling coils of air conditioning units is a major factor in moisture contamination of the system. The presence of condensation or high relative humidity is an important indicator of the potential for mold growth on any type of duct. Controlling moisture can often be difficult, but here are some steps you can take.

To prevent ducts from becoming wet:

  • Promptly and properly have any leaks or water damage repaired.
  • Pay particular attention to cooling coils, which are designed to remove water from the air and can be a major source of moisture contamination of the system that can lead to mold growth.  Regular maintenance on your cooling system can prevent this.
  • Make sure the condensate pan drains properly. The presence of substantial standing water and/or debris indicates a problem requiring immediate attention.
  • Check any insulation near cooling coils for wet spots.
  • Make sure ducts are properly sealed and insulated in all non-air-conditioned spaces (e.g., attics and crawl spaces). This will help to prevent moisture due to condensation from entering the system and is important to make the system work as intended. To prevent water condensation, the heating and cooling system must be properly insulated.
  • If you are replacing your heating or air conditioning system, make sure that the unit is properly sized for your needs and that all ducts are sealed at the joints. A unit that is too big will cycle on and off frequently, resulting in poor moisture removal, particularly in areas with high humidity. Also make sure that your new system is designed to manage condensation effectively.