How to Install a Bathroom Fan Timer Switch

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How to install a timer switch for a bathroom fan or light.

A simple electrical device can save you a lot of money in electrical, heating and cooling costs, they will also improve the indoor air quality (IAQ) or your home; an automatic timer switch. You can install these devices when upgrading your bathroom or add them to your existing exhaust fan to automatically turn off the fan after a set number of minutes.

Timer switches can be electronic or mechanical style devices, the mechanical timers use a dial while the electronic typically have a push button style. Mechanical timers offer more adjustment than electronic timers which typically have preset time positions on the switch. The loads ratings vary but are typically between 400 and 800 watts.

Installing a timer on an exhaust fan will save the homeowner money by not exhausting conditioned air to the outside and by not having the fan run longer than required. Exhaust fans are also required in bathrooms or powder rooms that do not have a window so if you are planning on putting your home on the market, you may want to correct this violation before potential buyers see the home. Exhaust humid bathroom air also prevents mold growth by removing moisture from the room after showering or bathing. Set it to run for 5 or 10 minutes after use top completely ventilate the room.

Mechanical Dial Type Timer


Electronic (Decora) Type Timer

Bathroom fans are one of the most common items, in a home, that are left on after use which can be easily corrected by replacing the wall fan switch with an automatic timer.

If you can replace a basic light switch, you can replace your fan switch with a timer. There are a wide variety of models available, but they basically all perform the same function. After a period of time, set by the homeowner, the switch shuts off, removing the electricity from the fan motor.

Mechanical timers need to be turned past 5 or 10 minutes to activate. Electronic timers have settings that you can select. Most also have an indicator light to let the user know how long the fan will remain on.

Wiring is fairly easy, but can vary between manufacturers. Basically the timer is wired in line with the hot side of the circuit (black or red) and the neutral wires (white) from the device and the switch are wired together.

Wiring diagram for a timer switch

The electronic timer uses a printed circuit board to control the operation of the timing of the switch. Dial type timers are mechanical that use a clockwork mechanism to perform the timing function. Mechanical timers are less expensive, but may be more susceptible to breakage than an electronic timer.

It should be noted that various timers have different load characteristics and it is important that you choose a timer that can handle the circuit load that you wish to control. Using a lower rated timer than the load will result in premature failure of the timer.

Motion Detector

Another option would be to install a motion detector. A motion detector would require a two-gang box to allow for the installation of the switch, but it would provide automatic operation anytime someone enters the bathroom or powder room. Most motion detector switches can operate loads up to 600 watts which is more than enough capacity for an exhaust fan and light.

Motion detectors are typically installed with a Decora style cover plate that comes with the device.

Below is a typical wiring diagram. Note: The load is the fan or light fixture.