How to Install a Bath Fan Timer


timer light switch

Would you like to guess what my most frequent piece of advice is for homeowners to improve indoor air quality, comfort, and to help save energy? It isn’t air sealing, installing new windows (try dead last for that one), adding insulation, or anything else similar to that.

Quite simply, it is to install a $20 timer for the bathroom vents. As luck would have it, I had to replace a few in my place (thanks kids…). And I thought I’d show you the process of installing a bathroom fan timer.

Before we do get started, please use some common sense. Get help from a licensed electrician if needed. While this is a pretty easy DIY task, it doesn’t take much to get shocked, burned or even start a fire if you don’t know what you are doing.

If you find that you have aluminum wires you would probably be better hiring an electrician. At least make sure your timer is compatible with aluminum wiring & use the special anti-oxidant cream as needed.


In this article, we will cover Replacing an existing Bath Fan Timer. Many of these steps will also apply to Replacing a Standard Switch with a Bath Fan Timer. The Bath Fan Timer used in this article is located on Amazon, here.

For more on Working with Electricians and the basics of the craft, see our category, Electrical. For a Quick Tip on Removing Back Stabbed Switches, jump to that below.


Replacing a Bath Fan Timer

– Let the game begin – in this case we already had a timer installed, but I will show you both switches.

bath fan timer double switch

– If you do have an older timer like this, simply pull the knob off & remove the small nut.

removed bath fan timer knob

*Remove the Switch Plate

– Once you unscrew the plate, I always like testing my tester to make sure the battery is still good.

testing power with electrical tester

*Turn off the Breaker

– Turn off the appropriate breaker – I generally cover it with electrical tape so no-one comes by & goes, ooh that should be on…

eletrical tape over breaker during workeletrical tape over breaker during work

– It always pays to double check that the power is completely off where you are working. As we have shown before, it is amazing what some people will do with electric when they don’t know any better.

For more on understanding your breaker box, please see our article – Making Sense of the Breaker Panel.

check power on switch even with breaker off

*Remove the Existing Switch

– Unscrew the existing fan switch. Tip: I always recommend taking picture of the wiring & the connections before undoing it any further as some boxes can be quite unique.

unscrew electrical switches take picture of wiring

*Working with a Back Stabbed Switch

– The existing timer had a screw accessible from the front for loosening up the wires. Now if you have a switch as shown on the right it will either be back stabbed or screwed into the terminals.

  • If it is screwed in just loosen the screws.
  • If it is back stabbed you generally will also have to loosen the screws &/or insert a small regular screwdriver into the slot shown to release the wire

electrical switch rear diagram

*Wiring the Bath Fan Timer

– Depending on your timer, you may either have to use wire nuts, back stab, side stab or attach it via side screws. Each package will have directions on what is required & which wire goes where. In our case, we have three stranded wires that one should twist gently in a clockwise fashion.

Going off the timer on the right – the two black go together & the green goes to ground. If the timer was replacing the switch on the right one of the black wires would go to black, the other would go to the white & the green would still go to the ground.

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black wire to black wire

*Mount the Fan Timer

– Once you are done wiring the timer up, reinsert it into the wall & tighten it down. Go turn on the breaker & test it out. If everything works fine, install the plate, pat yourself on the back, & go talk to everyone about how to use it, why & when. Then feel free to relax (or get busy with the next item) and enjoy your beverage of choice – Butterbeer anyone? : )

installed bath fan timer

In case you are wondering, my second & third most frequent piece of advice unfortunately revolves around not only bathroom ventilation but also dryer vents as many are not vented to the outside & they haven’t cleaned in ages.