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For your family's optimal health and comfort, your home's relative humidity levels should range from 30 to 50 percent in the winter and from 40 to 50 percent in the summer. But keeping humidity at these levels often demands mechanical assistance. For example, on sultry summer days, when indoor humidity rises above the comfort range, many people turn on air conditioners or dehumidifiers to help dry the air. And when the dry winter heating season sets in and drops relative humidity to skin-chaffing lows, boosting the humidity usually calls for a humidifier. Here we'll take a closer look at humidifiers: the main types, how they work, and what you should know if you're shopping for one.
A humidifier is simply a device that puts water vapor into a home's air. Depending upon its water output capacity, it may serve a single room or the entire house. Room-size humidifiers are referred to as "tabletop" units. To humidify a whole house, you need either a freestanding cabinet "console" unit or a "central" humidifier that ties into the home's forced-air heating system.
Tabletop and console models are relatively inexpensive, easy to move from one room to another and easy to hook up. Both types must be filled manually--usually on a daily basis. Regardless of the method they use to humidify air, tabletop models run from about $19 to $70, consoles from $75 to $150. Tabletop units output from 2 to 4 gallons per 24 hours. Small consoles output 8 gallons per 24 hour period--these can handle up to a 2000 square foot area. A large console may output 14 gallons, enough to humidify a 3,250 square-foot house.
Central humdifiers are hooked up to the heating equipment and water is piped directly to them, so they're out of sight and out of mind most of the time. Because they deliver humidified air directly to rooms throughout the house, they're particularly efficient . The only drawbacks are that you need a forced-air system to operate a central humidifier and humidification takes place only when the forced-air system is running (this isn't a problem in most homes because it is generally the heating process that dries out the air). Equipment prices range from about $140 to $200; installation cost depends upon the complexity of the work, but is likely to run about $100.
Most console and all central humidifiers are controlled by a humidistat that turns the unit off and on when humidity levels stray from a set range. Though a humidistat allows more or less "automatic" operation, you need to dial it up and down as the temperature changes in order to maintain fairly constant indoor relative humidity levels.
To put moisture into the air, humidifiers use one of four different methods:
Steam. Some humidifiers disperse water vapor into the air the same way a tea kettle does: by boiling water. Steam units are manufactured as tabletop or wall-attached models that spray steam into a living space or into forced-air heating ductwork through a dispersion tube. Except for tabletop models, tap water is piped directly into a steam unit, so that it doesn't require manual filling. Because steam is evaporated water, it doesn't contain bacteria or mineral deposits that might contaminate the air you breathe.
Ductwork systems, which are manufactured for both commercial and residential applications, can be custom-designed to output any amount of steam a house might need--though custom units may be prohibitively expensive for most home applications. And they can be costly to use; steam units employ an electrical heating element to heat the water; when this is on for extended periods, it can rack up energy dollars.
Ultrasonic. Though ultrasonic humidifiers were the rage a few years ago, they've fallen into disfavor because of the suspicious "white dust" that they create. With ultrasonic humidifers, a thin sheet of water is passed over a transducer that vibrates and excites the water, breaking it into millions of tiny droplets. The problem is that calcium and other minerals in the water become airborne with the moisture, particularly in areas that have hard water. This ends up as a dust that falls on objects in the room and pollutes the air you breathe. The Environmental Protection Agency (EPA) has warned that the tiny particles of minerals and microorganisms that may be propelled into the air may cause illness or allergies.
Cool mist impeller. This type of humidifier spins tiny droplets of moisture into the air. Available primarily as tabletop units, these hold from 2 to 3 gallons of water, are filled manually, and are easy to move around. They don't have the same problem with white dust that ultrasonic units have because the droplets produced are larger . Unlike steam humidifiers, cool mist units use electricity only to propel the air--not to provide heat. This means they consume far less power.
Evaporative humidifiers. Evaporative humidifiers, the most popular technology today, capture virtually all minerals and pollutants from even the hardest water, eliminating the white dust ultrasonic humidifiers can create. These work by passing an air stream through a wet medium, such as a sponge or dampened grill. Some have fiber honeycomb-type panels that wick water upward from a reservoir; others employ a foam or cloth drum that spins through a water-filled trough as air passes by. Still others blow air through a woven aluminum pad that is saturated by a constant stream of water. In some cases, filters are treated with a special compound that retards bacterial growth.
With tabletop and console models, a quiet fan blows air through the damp surfaces; some whole-house models use the heating system's blower to do this job. A filter collects the dissolved solids left behind by the evaporating water; this is generally disposable.
Central evaporative humidifiers are made to be attached to the home heating system, too. Their output capacities range up to 25 gallons per day. High-capacity models are fan powered; the others don't require a motor. All are hooked up directly to the plumbing so manual filling isn't needed.
One newer product that Emerson offers has no moving parts, electric cords, hot water or even a motor. Ideal for a child's room, this unit sits directly over a forced-air floor register and can be easily moved from one place to another. It retails for about $20.
Selecting the Right Humidifier
The Association of Home Appliance Manufacturers (AHAM) tests room humdifiers using uniform testing methods to verify water output ratings and to allow consumers to accurately compare models. For AHAM's Directory of Certified Humidifiers, send a personal check or money order for $5.00 to AHAM, 20 North Wacker Drive, Chicago, IL, 60606. Note the publication's name in your correspondence.
When buying a tabletop humidifier, check to see whether or not it has a humidistat and the number of speeds or settings it has--some have two or three speeds or a quieter night setting, for example. Types of controls are also important on a console humidifier. It should have a low-water light, automatic humidistat, and air-flow controls. Multi-speed and variable air-flow settings and an automatic shut-off are also helpful. Some models even have a light that goes on when the filter is dirty.
For any type of humidifier that must be filled manually, find out how often it must be refilled when running at full speed.
If you're looking into a central humidifier, be sure it can be installed relatively easily, considering the configuration of your heating system . In most cases, maintenance is limited to changing a evaporator pad about once a year--this component should be easy to inspect and access.
Central units are sold at home-improvement centers or by heating equipment dealers. If you're an accomplished do-it-yourselfer, a dealer can help you with proper sizing, making sure you have all the necessary components, and installation advice. If you haven't done this type of work before, have the unit professionally installed.
To insure lasting and safe performance of a humidifier, be sure to follow manufacturer's directions for use and care.
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