By running a bath or by having a shower, the bathroom produces high levels of moisture in a very short period of time, which will quickly condense unless conditions are such so as to prevent it. To create an environment 
that prevents this from occurring, an extractor fan capable of extracting fifteen to twenty air changes per hour is essential. However, different to the kitchen, the bathroom has special requirements, due, mainly to the presents of water in the vicinity of an electrical unit. With this in mind, fans have been designed that can remove the danger of electric shock by using a low voltage, 12-volt unit, or by using a fan designed to make it difficult for the water to come in contact with any electrical parts. 12-volt extractor fans are an ideal option for the bathroom, as the power to drive these fans is supplied by a transformer. With the transformer sited outside the bathroom, the danger of electric shock is removed.
Other type of fans are also available, namely the type which are ducted. Though they are powered by 240 volts, the actual motor/fan is situated outside the room and the extracted air is drawn along the ducting to the fan, before being expelled outdoors.
A further development is an extractor fan that is fitted within the external wall, with the motor set back in the brickwork, out of splash range.
Ideally, a two speed fan gives greater control, where the higher setting provides the maximum required air changes (as calculated) and the lower providing reduced air changes where the conditions are more favorable.
Due to the potentially large volume of moisture that could be produced by any member of the family bathing or using the shower, consideration may not always be given to condensation as being a problem. For this reason, the bathroom can be a difficult room to control and it may be well worth considering a fan that is activated by the light switch, coupled with an 'overrun timer' facility, better still a humidity sensor. Humidity sensors constantly measures the level of moisture in the air and will automatically switch on the extractor fan when a given level of moisture content is reached. It also automatically switches off the fan when the level of moisture drops to an acceptable level.
