The two most common rooms of the house to find an extract fan are the bathroom and the kitchen - two rooms which are often very
humid and are prone to condensation. It is clear from this that the main purpose of an extract fan is to extract moisture from the rooms, in the form of steam.
The vast majority of domestic extract fans fix either into a window or outside wall. Both the wall fan and the window fan are identical in operation. A small electric motor drives a plastic fan which sucks air from the room, blowing it outside. Many models have automatic shutters, which are opened by a solenoid as soon as the fan is switched on. When the fan is switched off the shutters close, preventing any uncomfortable backdraught into the room. For this reason they are called backdraught shutters.
A common way of controlling the fan is to wire it into the lighting circuit of the room which it serves. When the light is switched on the fan will run. After the light is switched off some fans run on for a preset period, controlled by an overrun timer.
Further up the range more facilities are offered. Some fans work with a speed controller which is mounted on the wall in a convenient position. This can then be switched to high, medium or low speed, depending upon requirements. In addition, some configurations allow the motor to change direction, or blow air into the room instead of sucking it out. This is a particularly useful source of fresh air where there is no opening window, especially in hot weather.
