Though fans can be an integral design piece in any room, bathroom fans are critical to both the style and function of the space. Bathrooms are high-moisture and high-traffic areas in the house. Install fans to state building regulations and codes in order to ensure that bathrooms don't develop mould or sustain moisture damage to walls, ceilings or floors. The British building regulations contains a section on ventilation, which is called "Part F."
A window or on an exterior wall is the ideal location for a bathroom fan, but many bathrooms cannot accommodate such positioning. Instead, place bathroom fans in the ceiling opposite the door to guarantee the most fresh air flow throughout the room. Building codes also specify that if the room contains a fuel-burning device that produces fumes, the room must be large enough so that clean air will replace the fumes pulled into the room when the fan is on. You must fit bathroom fans with an adequate ducting system that dispenses the extracted air away from the room or the rest of the house.
Manufacturers divide bathrooms into zones that determine the voltage limitations for each area of the room. Zone 0 is the bath area; Zone 1 is the area above the bath. Zone 2 represents the space within a 60 cm (2 foot) radius from Zone 1, and Zone 3 represents a 1.8 to 2.1 m (6 to 7 foot) radius from Zone 2. A mains voltage fan with a voltage measure of 240 volts cannot be used in Zones 0, 1 or 2. A safety extra low voltage fan at just 12 volts is safe for use in all zones.
Size and Extraction Rates
The volume of the bathroom determines the necessary size and extraction rate of the fan. Multiply the length of the room by its height and its width to calculate the volume of the bathroom. Then multiply the volume of the room by the number of time per hour that the air changes in the room to determine the necessary extraction rate; in most standard bathrooms, the air flow rate is seven changes per hour. The British Building Regulations uses litre per second as its extraction rate unit of measure. Part F expects an extraction rate of 15 l/s for a bathroom and 6 l/s for a separate toilet room. If there is no openable window in the bathroom or toilet the fan should continue to run for 15 minutes after the light is turned off. This is termed the "overrun."