Begin by touring your household. Follow your nose, and use your eyes. Two major factors help create conditions for biological pollutants to grow: nutrients and constant moisture with poor air circulation.

Dust and construction materials, such as wood, wallboard and insulation, contain nutrients that allow biological pollutants to grow. Firewood also is a source of moisture, fungi and bugs.

Appliances, such as humidifiers, kerosene and gas heaters, washers and clothes dryers, dishwashers and gas stoves, add moisture to the air.

  • A musty odor, moisture on hard surfaces, and even water stains, may be caused by:
  • air-conditioning units;
  • basements, attics and crawlspaces;
  • bathrooms;
  • carpets;
  • heating and air-conditioning ducts;
  • humidifiers and dehumidifiers; and
  • refrigerator drip pans.