To prevent dirt from entering the ventilation system, use the highest efficiency air filter recommended by the manufacturer of your heating and cooling system and change filters regularly. When having your heating and cooling system maintained or checked for other reasons, be sure to ask the service provider to clean cooling coils and drain pans. If your heating system includes in-duct humidification equipment, be sure to operate and maintain the humidifier strictly as recommended by the manufacturer. Moisture is should not be present in ducts. The presence of condensation or high relative humidity is an important indicator of the potential for mold growth on any type of duct.

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 ventilation system work as intended.