Know your humidifiers

Do not buy a humidifier unless you are willing to clean it regularly, often daily. Microorganisms that readily grow in water -- including legionnella, which causes Legionnaires disease-- can be spewed into the air, making people sick.

The American Lung Association of the Upper Midwest recommends that humidifier tanks be emptied, wiped dry and refilled daily to reduce the growth of microorganisms. Using water low in mineral content (distilled water) prevents the buildup of scale and the dispersal of minerals into the air via nuisance white dust.

The four general types of humidifiers:

• Ultrasonic, which creates a cool mist by means of ultrasonic sound vibrations.

• Impeller, or "cool mist," which produces a cool mist by means of a high-speed rotating disk.

• Evaporative, which transmits moisture into the air invisibly by using a fan to blow air through a moistened absorbent material, such as a belt, wick or filter. (In-duct or whole-house humidifiers are mounted into the ductwork. The furnace fan distributes the moisture produced by the evaporative humidifier.)

• Steam vaporizer, which creates steam by heating water with an electrical heating element or electrodes. "Warm mist" humidifiers are a type of steam vaporizer humidifier in which the steam is cooled before exiting the machine. (Keep out of the reach of children. Steam and boiling water may cause burns.)

Remember to clean the humidifier as directed at the end of the season, making sure all parts are clean and dry before storage. Dispose of all used demineralization cartridges, cassettes or filters.

Have your whole-house humidifier serviced before turning it on in the fall.