HVAC help . Before you start using any heating or cooling appliances, have them inspected and cleaned by a professional. If, as part of your forced-air system, return vents are located in hallways, be sure to keep doors open to rooms without return vents. Otherwise air pressure and humidity differences between rooms could increase the concentration of allergens. Lowering humidity .
Dust allergens and mold and mildew thrive on humidity.
While relative-humidity levels between 30 and 50 percent are generally recommended for most households, a level of 35 to 45 percent may be more comfortable for allergy or asthma sufferers. You can control room humidity with a humidifier or dehumidifier. So check it frequently for mold and mildew, add fresh water every day to a room humidifier and clean it every three days. You should also check a dehumidifier on a regular basis. Today's Homeowner, a division of Times Mirror Magazines.