An exhaust fan works by using an electric motor to drive blades on a fan to remove heat and humidity from a space. The position of the fan and the unit used to control it determine how effectively the fan exhausts.
The primary function of an exhaust fan is to remove hot, humid air and replace it with cool, dry air. A closed room does not vent as well as a room with some sort of intake. Leaving a window or door ajar can help the fan circulate air. Placing the fan high up in the room increases its draw of hot air. The fan can be linked to a thermostat or humidistat to control when it is activated. A rheostat can be used to reduce the noise, speed and cubic feet per minute of a fan. Exhaust fans can reduce odor and indoor air pollutants.
Fans vary in strength, which is measured in cubic feet per minute. Choosing the right size fan for the space ensures that proper ventilation is achieved. Some fans have to be run through ducting to allow them to exhaust outside of the house. Any hard turns or angles in the ductwork reduce the ability of the fan to clear the room.