How to Slow Down a Bathroom Fan (3 options)


Sometimes it is necessary to slow down your bathroom exhaust fan. It might be because you are trying to save energy, reduce noise, or reduce cold drafts caused by excessive ventilation.

It is good to have a high CFM exhaust fan for short bursts of high intensity ventilation, but most of the time a more moderate speed would be more suitable.

This is where a bathroom fan speed controller will help you out.

The bathroom exhaust fan can be slowed down by a speed controller that is designed specifically for AC motors. A light dimmer should never be used to regulate the speed of a motor, this will damage the motor and could even cause a fire.

Next we will look at different types of speed controllers and how you can be sure you buy the correct one.

Variable Speed Bathroom Exhaust Fan Speed Controller

The best solution is to use a controller that is specifically designed for bathroom fans, they often include on/off switch as well and can completely replace your existing switch.

This will make wiring very easy since most likely all the wiring is already there behind the original fan switch.

Also there is no need for drywall work as it can be installed in place of the existing switch.

Keep in mind that you take into account how many amps your fan draws. It is wise to buy a controller that is rated for at least 25% higher than the exhaust fan.

For example: If you have a 0.5 amp exhaust fan then the controller should be rated at least 0.7 amps.

However, most likely this will not be a problem for you since most speed controllers are rated at a minimum of 2 or 3 amps. That is more than enough for even the most powerful bathroom fans.

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Three Speed Bathroom Fan Speed Controller

If you are not a fan (pun intended) of the round dial on the variable speed controller, then this is a great alternative. It works just like a normal switch, but there is an additional slider on the side for speed control.

This is very convenient if you like to keep the fan on a low setting for most of the time. You can easily boost the speed temporarily using the slider when necessary.

Wiring on both of them is the same and both can be a direct replacement for your existing bathroom fan switch.,

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Light Switch / Speed Control Combo

This is excellent if your current switch is a light/fan switch combo. This is the most expensive choice, but in my opinions the best.

If you have a 1-Gang wall box installed in your bathroom then using this will most definitely save you money.

Drywall and electrical works to add another wall box will be most likely more expensive than buying this.

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Will Slowing Down The Fan Make it Quieter?

Slowing down will dramatically decrease the loudness of the fan. Most small diameter fans run on very high RPM-s to achieve a high airflow.

Using the speed controller to reduce the speed by 20-30 percent will make the fan much quieter. This is excellent if you shower right before sleep and want to leave the fan running.

Then you can just slow it down to the point it does not disturb your sleep.

It is best to run the bathroom fan for at least 30 minutes after the shower to get rid of most of the moisture in the air.

Stop Cold Drafts Caused By Excessive Ventilation

Slowing down the fan will greatly reduce cold drafts caused by too powerful exhaust fans.

Cold drafts are more commonly caused by range hoods. After all, they move many times more air than bathroom fans however, in some cases bathroom fans can cause this as well.

Running the fan on max rpm-s can cause cold drafts in other parts of the house, especially in colder climates during the winter.

Using an speed controller is an excellent way to make your home more comfortable, while still maintaining minimum ventilation requirements.

Wiring The Fan Speed Controller

If you feel confident with electrical work then you could do this yourself, however, in most states it is illegal to carry out electrical work without a license.

Doing so can result in fines and trouble with your insurance provider in case of a an accident.

If you are feeling confident and still want to proceed, I will explain shortly how it is done.

Before you begin work double-check to see if the speed controller, light, and Speed controller/dimmer are compatible. This is very important as using too large loads on a small controller can cause overheating.

Fan speed control wiring

This is a general wiring diagram for a speed regulator/light dimmer combo. 2 wire fan and LED lights. It is important that you consult the manual of the controller you bought for wiring instructions.

If the manual was not included then you can easily find it on google by searching (product code+manual).

Conclusion

It is relatively easy and cheap to slow down the bathroom fan. There are many options on the market so you will surely find an option that is right for you. If you don’t feel confident enough to install the speed controller yourself an electrician can do it in about 20 minutes. Provided that you purchased the correct controller for your situation.

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Joonas Pütsepp

I like it when I'm able to fix everything that needs fixing around the house. In order to do that, I have to do a lot of research. This site will cover everything I learn and maybe help others do the same.

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