What is a Humidistat?

A humidistat is a mechanism that works in conjunction with space conditioning machines to regulate a room's humidity level. They are commonly used with air conditioners, humidifiers, and dehumidifiers, gauging the humidity in a given space. When used on a device with a thermostat, such as an air conditioner, a humidistat allows the unit to turn on and off when a predetermined level of humidity is present.

Humidistats ensure a room maintains a comfortable temperature and helps prevent mildew from forming. Certain rooms in a home are more sensitive to humidity and are more prone to the development of mildew. A bathroom humidistat attaches to the ventilation fan in the room, automatically cycling off once the humidity level has dropped. The upper stories of a dwelling also experience high degrees of humidity. An attic humidistat works with a fan to keep temperatures manageable and conditions inconducive to the growth of mildew.

There are many humidifiers and dehumidifiers that come equipped with a built-in humidistat. The user can program the device to read moisture levels in the air, setting it to function or switch off as humidity rises or falls. A dehumidifier or humidifier humidistat may be located directly on the machine or accessed through a remote control.

Thermostats are also available with incorporated humidistats. A thermostat humidistat allows users to set the temperature levels within a space while ensuring humidity remains at a minimum. Degrees of humidity can be adjusted to suit the user's personal preferences. The typical programmable range for humidity levels is 15%-45% relative humidity (RH). If the level in a room exceeds the desired amount, the humidistat will alert the thermostat to automatically turn on the air conditioner.

A digital humidistat is easy to read and adjust. It displays the temperature of the room, the level of humidity, and often will show the target temperature and level. Most models are simple to program with the preferred information, and many also include security settings that guarantee the unit runs properly even if the humidistat is tampered with.

Since humidity levels vary in different geographic areas, it is important to consult the humidistat manufacturer's guidelines to establish the optimal setting for a given locale. If the device is set improperly, it could cycle on when it is not needed, wasting energy and escalating utility costs. Most manufacturers include with each product a listing of ideal humidistat settings for a wide variety of locations.