Too much cold-weather humidity in a home can create problems such as window condensation and mildew. But a home that is too dry also can have problems.
Some of the symptoms of an overly dry house in winter are static electricity, cracking wood furniture, itching skin and eyes, and respiratory discomfort. Too-dry air also makes the occupants of a home feel colder, at a given room temperature, than they would in a properly humidified home.
Installing a humidifier can solve a dry-air problem, but the humidifier should be carefully chosen and controlled to avoid over-humidifying. It will also need regular maintenance, especially cleaning.
Before shopping for a humidifier, measure or estimate the square footage of the area to be humidified to help choose the correct size of unit needed.
Humidifying is simply a method of adding water vapor to the air. The amount of water vapor held by the air, technically called relative humidity, is expressed as a percentage of the amount of vapor the air could hold if it were saturated. The warmer the air, the more water vapor it can hold.
Most experts recommend an indoor relative humidity of 30 to 50 percent when the indoor temperature is at a typical heating-season level of 70 degrees. Readings of indoor humidity can be taken with a hygrometer, an instrument sometimes sold in combination with a thermometer.
How much additional cold-weather water vapor a home needs, if any, depends on the size and construction of the home and the lifestyle of the occupants. In most homes, a great deal of moisture is added to the air by vapor from baths and showers, cooking, laundering and watering plants. If the home is well-insulated and weather-stripped, much of this vapor will remain in the air, raising the relative humidity.
According to the Association of Home Appliance Manufacturers, a trade group, approximately five gallons of additional water should be added daily to the air of a “tight” or well-insulated home with 2,000 square feet of living space to maintain an indoor relative humidity of 30 percent. About 10 gallons of water must be added to the air of a poorly insulated home of the same size to maintain the same humidity.
For best results, a humidifier should be equipped with a humidistat or control that will automatically turn the humidifier on when more humidity is needed, and turn it off when a preset humidity level is reached.
In homes with forced-air heat (ducts and registers), a humidifier can be installed at the furnace so that water vapor, propelled by the furnace fan, is carried to each heated room along with the heated air. Humidifiers of this type generally have automatic water feed, run quietly and have high vapor output. Since they are installed on or in a main duct, they take up little extra space. Central humidifiers generally have pads, which perform like wicks to help distribute the moisture. The pads should be changed regularly. Regular cleaning is also needed to prevent buildup of minerals and bacteria.
Central humidifiers suitable for do-it-yourself installation are available at some home centers and building-supply outlets. A typical central unit sells for about $75.
A variety of console and tabletop humidifiers is also available, most of them priced at less than $150. Most experts say the best and safest of these are evaporative and warm-mist humidifiers.
Evaporative humidifiers use wicking filters or pads to draw water out of a reservoir. Air is blown through the pads by a fan or fans, forcing moisture-laden air into the room. Mineral deposits from the water remain in the reservoir or on the pads, instead of being expelled into the air as they are with some types of humidifiers.
Water is boiled in warm-mist humidifiers, but the steam is cooled before it is expelled into the air. Some warm-mist humidifiers include medication containers so they can be used as vaporizers.
Tabletop humidifiers are best suited to humidifying a single room. Larger console models can serve several rooms or even an entire house.
