Mold Web Course/Chapter 2/Lesson 4

by the Environmental Protection Agency

Lesson 4Ventilation Humidity Problems - Heating, Ventilation, and Air Conditioning (HVAC) System

Mold growing near the intake to an HVAC system indicates potential ventilation humidity problems. An HVAC system that is part of an identified moisture problem may also be a site of mold growth. Experience and professional judgment should be used when working with the HVAC system; consult a professional if needed.

The HVAC system has the potential to spread mold throughout a building. Known or suspected mold growth in HVAC ducts or other system components should be investigated and resolved promptly. If substantial amounts of mold can be seen growing on the inside of hard surface ducts (e.g., ducts made of sheet metal), consider cleaning the ducts. Consult the EPA guide Should You Have the Air Ducts in Your Home Cleaned? (see the Resource List). Although this publication focuses on ducts in homes, the information it contains is applicable to other building types.

If the HVAC system has insulation on the inside of the air ducts, and the insulation gets wet or moldy, it should be removed and replaced because the material cannot be cleaned effectively. Please note that there are no antimicrobial products or biocides approved by EPA for use on lined ductwork. Consult the EPA Web site on antimicrobial pesticides for more information (see the Resource List).

Controlling moisture is the most effective way of keeping mold from growing in air ducts. Steps to control moisture in ductwork include:

• Promptly and properly repairing any leaks or water damage.
• Removing standing water under the cooling coils of air handlers by making sure the drain pans slope toward the drain and the drain is flowing freely.
• Making sure ducts are properly sealed and insulated in all non-air-conditioned spaces so moisture due to condensation does not enter the system and the system works as intended. To prevent condensation, the heating and cooling system must be properly insulated.
• Operating and maintaining any in-duct humidification equipment strictly according to the manufacturer's recommendations.
• Making sure that carpets, drapes, furniture, and other furnishings are dried promptly after they have been cleaned.