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Cold air holds little moisture. When it enters the house and is warmed, the air in the house becomes uncomfortably dry. This dryness, in addition to causing personal discomfort such as respiratory distress and dry skin, can wither house plants, loosen joints in furniture and even crack paintings. It is also the prime cause of static electricity.

This dry-air problem can be solved with a humidifier, which can also cut heating bills.

Humidity can be checked with a humidiguide. Generally recommended inside humidity values are:

Outside Temperature Desired Humidity
-10 degrees F 20%
0 degrees F 25%
+10 degrees F 30%
+20 degrees F 35%
+30 degrees F and above 35%

However, if the house is not of reasonably tight construction and does not have storm windows, it may be necessary to sacrifice some humidity to avoid excessive condensation on the inside of windows.


The number of cubic feet a portable humidifier will moisten depends not only on output but also on such factors as rate of air exchange in the house from outside, washers and dryers in use, showers in use, etc.

A unit with good moisture output, about 2-3 gals. of water a day, can raise humidity in a four to five room house to the levels in the accompanying table. Smaller models will release .5-1.5 gals. a day.

One type of humidifier uses a revolving belt made of foam rubber or a washable plastic that absorbs water from a built-in tank.

Another type uses an impeller to pump water to the top of the unit where it flows over a filter. As the water descends by gravity through the filter, dry air is drawn by a fan through the filter, moistened and diffused through the grille.

Water in both types is evaporated by a motor driven fan. Fan sizes vary from about 8″ to 12″. Revolving belts have 1,000-1,500 sq. in. surfaces. Tank capacities vary from 5-10 gals. The difference in tank size has no effect on the efficiency of the unit; it only means that smaller tanks will need to be refilled more often.

To help fill the tanks, some models include a filler hose that connects to a faucet. Models without a hose may be filled from a bucket or jug.

Better models have adjustable fan speeds, a built-in humidistat and automatic shutoff.

Portable humidifiers should be placed near an inside wall, preferably facing a stairwell, and at least 6″ from the wall for proper air circulation. Since moist, warm air rises, a unit placed on an upstairs floor will not be as effective.

Ultrasonic humidifiers moisten the air through the use of ultrasonic sound waves. The sound waves are used to vaporize the water particles in the water reservoir into a cool vapor mist. In addition, these humidifiers are very quiet. Some feature an automatic shutoff switch in case the unit is tipped over or the tank empties.

The Environmental Protection Agency found that these humidifiers appear to raise the level of airborne particles in the home beyond acceptable levels. The machines combine bacterial residue and mold with other pollutants in the water and spew the mixture around. To combat this problem, use distilled water, clean the machines frequently and empty them between uses.

Another less-serious problem is the white dust the humidifiers spread around the house. The white dust consists of pulverized minerals from the water. Most devices have filters to combat this problem. Depending upon the hardness of the water used in the humidifiers, these filters must be changed from two weeks to once a season.


Furnace mounted humidifiers force dry air from the furnace through a saturated foam element or plate. This type of humidifier is sold complete with a length of copper or plastic tubing to connect to the water supply, and the humidifier is refilled automatically.

Another type of furnace- mounted humidifier sprays a fine mist of water into the heated air.

An automatic reset humidistat will adjust moisture output to compensate for weather change. Evaporative elements are replaceable at minimal cost.

Self-cleaning units reduce messy cleanups and eliminate the need for water additives. Adequate moisture is supplied in less time, eliminating wear and tear on the humidifier and conserving energy.

For homes heated by hot water, electricity or steam, special humidifiers can be placed in closets, laundry and utility rooms or basements, etc., with outlets leading into living rooms.


Maintenance cost of a humidifier is low, and the unit uses little electricity. It will lower heating costs and pay for itself in a short time. Low humidity makes a house feel colder than it actually is; thus, when the humidifier is installed, less heating is required to maintain a comfortable temperature.

Tanks and filters or belts should be cleaned regularly. Be sure to watch for scale formation in humidifiers. This accumulates as a residue of minerals when water evaporates. Formations clog filters, pads and belts to the extent that they cannot pick up or hold water. This reduces performance and can lead to equipment damage.

There are ways to get rid of the scale with liquid de-scalers. Periodic use is essential for good performance. Another way to solve the problem is to treat the water. Concentrated water treatment for console humidifiers reduces scale buildup and controls mold and mildew growth.

Check your state and local codes before starting any project. Follow all safety precautions. Information in this document has been furnished by the North American Retail Hardware Association (NRHA) and associated contributors. Every effort has been made to ensure accuracy and safety. Neither NRHA, any contributor nor the retailer can be held responsible for damages or injuries resulting from the use of the information in this document.