In the winter, it is especially important to add moisture to the air, since dry winter air can decrease the relative humidity level in your home to as low as 15 percent, which is drier than the air in most deserts. A whole house humidifier works with your central heating and cooling system to help keep the humidity in your home at the proper level. It even saves money on winter heating bills because properly humidified air feels warmer, allowing homeowners to turn their thermostats down a few degrees.
Unlike portable room humidifiers, which need continual adjustment and regular manual attention, whole-house humidifiers automatically respond to changes in outdoor temperature and indoor relative humidity to deliver whole-house humidity.
Some whole-house humidifiers come with a built-in fan that circulates humidified air throughout your home through the furnace’s duct system. Other types use the air handler or furnace fan to direct humidified air to every room in your home.
The evaporative humidifier operates in tandem with the furnace blower motor. When the humidistat, a device that measures the amount of water vapor in the air and turns a humidifier or dehumidifier on and off accordingly, calls for humidity and the blower motor is operating, water flows to the distribution pan located at the top of the unit. The water is uniformly distributed across the width of the pan and through a system of outlets. It flows by gravity over the evaporative media filter. Dry, hot air is moved through the moisture-laden evaporative media where evaporation takes place.
The now-humidified air carries moisture in vapor form everywhere in the home. The correct water flow is determined by an orifice in each unit. When the unit is operating, there will be a small, steady stream of water to drain, which flushes away most trouble-causing minerals contained in the water supply. Minerals and solid residue not trapped by the replaceable evaporative media are flushed down the drain. The drain also eliminates problems caused by stagnant water.
Whole house humidifiers are usually controlled by a manual humidistat installed either in the living area or in the cold air return. It is important to anticipate a drop in temperature and lower the setting accordingly to avoid excessive condensation. For example, with an outside temperature of 20 degrees Fahrenheit the correct setting will be 35 percent relative humidity. If the temperature is expected to fall to 0 degrees Fahrenheit that evening, reduce the setting to 25 percent several hours prior to the temperature change. Observance of the recommended relative humidity level on your humidistat is an important safeguard.
Condensation in the form of fogging or frost on inside windows is typically an indication of excessive relative humidity. The same condensation can take place in other areas in your home with the possibility of resulting damage.
Be sure to keep fireplace dampers closed when not in use. They provide a superb escape route for heat, as well as humidity.
Source: Air Conditioning & Refrigeration Institute