The most common humidifiers are called evaporative or wick humidifiers. The most common type of humidifier, the wick humidifier, basically has three parts: a reservoir, a wick, and a fan. Humidifiers work by evaporating water into the air, thereby increasing relative humidity levels. As the humidity level increases, less water will evaporate. This means that the process regulates itself very well.
The wick absorbs water from the reservoir, and a fan blows air past the wick. This helps to evaporate the water into the room air. The wicks need regular cleaning and replacement. A room with low relative humidity will absorb more water into the air than a room with a higher relative humidity. After a time, the humidity level in the room will reach a state of equilibrium. This means it won’t absorb any more water into the air unless the humidity level drops, or the temperature goes up.
Another major type of humidifier is called the forced-air humidifier. The forced air humidifier is usually attached directly to the house furnace. There are two basic models of forced-air humidifiers, the drum style, and the flow-through style. Unfortunately, most modern, highly-efficient forced air furnaces don’t run long enough when heating to let much water get absorbed into the air. Many people choose to supplement the forced air humidifier with a room humidifier.
The drum style humidifier should be turned off during the summer, and the reservoir pan emptied. This will help to prevent mold growth when the humidifier is not needed.
There are a couple more humidifiers, a vaporizer which heats water to steam and disperses it into the air, an impeller humidifier, and an ultrasonic humidifier. These are generally room humidifiers.