Warm Mist HumidifierWhen the weather grows cold and home heating systems are turned on, the air in the home can become dry.

A humidifier can be used to relieve discomforts caused by dry air, such as chapped lips, dry skin, dry noses and scratchy throats. A humidifier can also be useful for relieving congestion.

A humidstat is dialed up and down to control the level of humidity. A tabletop humidifier is designed to humidify a single room and can be moved around the house. To humidify an entire home, a console humidifier or central humidifier is needed.

A console humidifier is a freestanding unit, and a central humidifier is connected to the home's central heating system. Both the tabletop and console humidifier must be manually filled with water at regular intervals, but a central humidifier is connected to water and does not need to be refilled by hand.

Humidifier types include forced air, evaporative, steam vaporizer, self-cleaning, impeller, and ultrasonic types.


Evaporative humidifiers are also called wick humidifiers. This technology is simple and the commonest type used. It consists of a wick, fan and reservoir housed in a single casing. It works by the wick absorbing water from the reservoir, with a fan blowing ambient air onto the wick, thereby driving further wicking action and blowing humidified air into the room.

Evaporation of water from the wick depends mainly on the process of relative humidity. A room having low humidity will naturally have a higher evaporation rate than a room with high humidity. That makes this type of humidifier self-regulating: As humidity in the room increases, the wick’s water vapor output decreases. The disadvantage of this is that the wick needs frequent cleaning and/or replacing or the process will not work effectively.

Mist Humidifiers

Also called vaporizers, these work by boiling water, and releasing moist steam vapor into the air. Although they use more electrical energy than cool mist humidifiers, they are healthier because the steam is sterile and free of contaminants such as bacteria, mold viruses and minerals.

In a cool mist humidifier, a diffuser breaks water into fine droplets which disperse into the room air from an impeller disc. Ultrasonic humidifiers work on a similar principle, except that a metal diaphragm vibrates at an ultra high frequency to break up the water into a cool mist. The amount of bacterial and mineral contaminants can be reduced by using distilled water.

Distillation is the most effective method for removing minerals from water. De-ionization and reverse osmosis both remove most of the minerals from water, but in general are less effective than the process of distillation.

Water demineralized by these two processes would generally contain a higher mineral content than distilled waters. Water labeled as "Purified" can be produced by any of these three or other similar processes; only water that has been distilled can be labeled as “Distilled”.

Forced Air Humidifiers

For homes with central heating systems, a whole house humidifier is an option. Built into the furnace unit, these are also called Bypass Humidifiers, since they are installed between the heated and cold air return ducts. They use the pressure differential between the two ducts to cause a portion of the heated air to make a bypass through the humidifier and then return to the furnace.

Since air conditioners function in part by removing humidity from the environment, this type of humidifier should be turned off when air conditioning is in use, as they will be wasting energy and produce no benefit.

Care of Humidifiers

It is essential to use a humidifier only when conditions dictate it, and also to use the proper humidity setting for existing conditions, and thoroughly clean it. Health effects stemming from the dispersal of microorganisms and minerals via home humidifiers are not fully understood.

Until then, it may be prudent to reduce any possibility for personal exposures to contaminants through taking the precautions, particularly when using cool mist ultrasonic and impeller humidifiers. Here are some tips to help, courtesy of the U.S. Environmental Protection Agency:

    • 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.

    • Use water with low mineral content to prevent the build-up of scale and the dispersal of minerals into the air. See the box on the left for information on using water with low mineral content.

    • 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.

    • Follow the 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.

    • Follow the manufacturer's directions on cleaning and maintaining console and central (furnace mounted) humidifiers. In particular, if the humidifier contains a tank, do not allow water to stand in the tank for extended periods of time, and keep the water clean.

    • Keep steam vaporizer humidifiers out of the reach of children. Steam and boiling water may cause burns.

    • Do not humidify to indoor relative humidity levels exceeding 50 percent. Higher humidity levels may encourage the growth of biological organisms in the home. Hygrometers, available at local hardware stores, may be used to measure humidity levels. Some humidifiers contain a built-in humidistat which may be adjusted to the proper moisture level. If water condenses on windows, walls, or pictures, either (a) relocate the humidifier, (b) lower its humidistat setting, or (c) reduce its use.

    • Do not permit the area around the humidifier to become damp or wet. If dampness occurs, turn the output volume of the humidifier down. If the humidifier output volume cannot be turned down, use the, humidifier intermittently. Do not allow absorbent materials, such as carpeting, drapes, or table cloths, to become damp.

    • 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.

    • 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.

    • Stop using your humidifier and contact your physician if you have respiratory symptoms which you believe are associated with periods of use of your home humidifier, even if you are following maintenance directions.

Photo by Jeremy Noble, Creative Commons Attribution License