Humidifer Health and Safety

Miriam Stevens, Clean Air Advice
September 2006

Dry winter air, especially when combines with home heating, can contribute to uncomfortable dryness and irritation of the nose, throat, lips, and skin, as well as household nuisances such as peeling wallpaper, static electricity and cracking paint and wooden furniture. A simple and inexpensive remedy is to use a humidifier, which releases mist into the air, raising the humidity in the room.

Humidifiers come with their problems, however, because excess moisture can encourage the growth of biological organisms in the home, including dust mites and mold, both of which are implicated in allergies and other respiratory problems related to poor indoor air quality. Recent EPA studies suggest that ultrasonic and impeller humidifiers, also known as "cool mist" humidifiers, can disperse both microorganisms and mineral pollutants into the air. Breathing these pollutants has been linked to a malady called "humidifier fever," an inflammation of the lungs and breathing passages.

Young children, the elderly, and those who have respiratory problems or lung diseases are particularly susceptible to certain types of airborne pollutants, including the minerals, bacteria, and molds released from household humidifiers. But by following a few simple tips, you can greatly reduce the potential problems caused by your humidifier.

Humidifier Types and Potential Pollutants

Home humidifiers may be a central unit built into the central HVAC system, smaller console-mounted units designed for floor use, or smaller portable units, but they all generally fall into a few basic types:

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

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

Evaporative, which transmit moisture into the air invisibly by using a fan to blow air through a moistened absorbent material, such as a belt, wick, or filter.

Steam vaporizer, which create 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.

Typically speaking, studies have shown that Ultrasonic or Impeller humidifiers are among the worst offenders when it comes to mold and mineral dust pollution. But while evaporative and "warm mist" humidifiers have not been shown to release significant amounts of molds or bacteria into the air, be aware that mold can grow in any humidifier which uses a tank of standing water. Excessively humid conditions may also contribute to condensation on walls and other surfaces, which also encourages mold to grow. The first tips of humidifier use in the home is to only use a humidifier when you need it: most recommend keeping the indoor humidity at or below 50-55%. You should also position your humidifier at least a few feet away from walls and furniture, if possible.

Humidifier Use and Care

It is important to use a humidifier only when conditions require it, to use the correct moisture setting for existing conditions, and to clean it thoroughly and frequently. The possible health effects resulting from the dispersal of microorganisms and minerals by home humidifiers are not yet fully understood, but it's prudent to reduce the potential for personal exposures to these materials by taking the following precautions, particularly when using ultrasonic and impeller humidifiers.

Refill Daily: Empty the tank, wipe all surfaces dry, and refill the water in portable humidifiers daily to reduce any growth of microorganisms; follow the manufacturer's instructions for changing water in console humidifiers. Be sure you unplug the unit from the electrical socket first. For console or central HVAC systems, avoid letting water stand in the tank for extended periods of time.

Use Low-Mineral or Distilled Water: Use water with low mineral content to prevent the build-up of scale and the dispersal of minerals into the air. Distilled water may still contain some minerals, but may the best bet, particularly if your home has "hard water." Look specifically for "distilled water;" water labeled "artesian" or "spring" water has not been demineralized, and may make matters worse.

Regular Cleaning: Clean portable humidifiers every third day. Empty the tank and use a brush or other scrubber to clean it. Remove any scale, deposits, or film that has formed on the sides of the tank or on interior surfaces, and wipe all surfaces dry. Again, be sure you unplug the unit first.

Disinfect: Follow manufacturer's suggestions on the use of cleaning products or disinfectants. In the absence of specific recommendations, clean all surfaces coming in contact with water with a 3% solution of hydrogen peroxide. If you use any cleaning or disinfecting agent, rinse the tank thoroughly with several changes of tap water to prevent dispersal of chemicals into the air during use.

Don't Overdo It: Do not humidify to indoor relative humidity levels exceeding 50 percent. Higher humidity levels may encourage the growth of molds and bacteria in the home. Look for a humidifier with a built-in humidistat to maintain moisture level, or use a hygrometer, available at most hardware stores. If water condenses on windows, walls, or pictures, either relocate the humidifier, lower its humidistat setting, or reduce its use.

Replace Filters and Wicks: Follow the manufacturer's instructions regarding the use, maintenance, and replacement of any materials supplied with the humidifier. Use appropriate materials as recommended by the product manufacturer.

Season Cleaning: Clean the humidifier, as directed, at the end of the humidifying season or when the product will not be in frequent use. Before storage, make sure all the parts are dry. Dispose of all used demineralization cartridges, cassettes, or filters. Store the unit in a dry location. After storage, clean the unit again and remove any dust on the outside.

Final Note

Following these simple tips, and using a little common sense, should give you the best chance of using your home humidifier safely. But should you experience any respiratory symptoms you think may be related to your humidifier use, discontinue use immediately and seek the advice of your physician.

Related Articles

• Biological Pollutants
• Do You Have a Mold Problem?
• Cleaning Your Home or Office HVAC System
• What Are You Breathing?
• 12 Steps to Improve Indoor Air Quality