At a minimum, bathroom fans should be run during any period of high moisture production: showers and baths. It is also a good idea to run them for 45 minute or so after this period of time.

In some homes, bathroom fans are also used as a part of the "whole house" ventilation system. In that case the fans should be run for a minimum of about 1.5 hours, 2 times per day and 365/yr. In cases where such fans are used as the exhaust system and the air intake is part of the furnace or other fan, the bathroom fan should be coupled to the intake fan timer. When fans are operated by a remote timer, the switch in the bathroom allows one to turn a fan on even when the timer is off.

Here are some other fan control options:

• The simplest individual control for a bathroom fans is the light switch. When the light is on the fan is on and when its off... But this does not allow for independent fan and light operation.
• Two switches can work fine but they require "operator" education and that maybe a problem with children and tenants.
• A timer is a more sophisticated version of the two switch system. This method also requires operator discipline.
• It is also possible to run fans by a local switch and a remote times. This allows for "local" control but also assures that the fan is run for a minimum amount of time during every day.

and the bathroom door... In order to allow for good fan operation and promote some additional air movement in the home it is always a good idea to undercut the bottom of the bathroom door by an inch or so. If the bathroom is hermetically tight the fan will not be able to operate efficiently and can't be a functioning part of a whole house ventilation system.