Why Does My Bathroom Fan Turn on by Itself?

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The most common reason why a bathroom fan turns on by itself, is that it is connected to a humidity controlled switch. Whenever the humidity level rises above a set point it will turn on automatically. The turn-on humidity setting can be adjusted on most switches.

Though this problem is seemingly uncommon, it can be incredibly frustrating to deal with. If you have a loud fan, it can be especially annoying if it turns on for seemingly no reason.

Humidity levels change with the seasons. If the humidistat was set during the wintertime when indoor air is relatively dry it will most likely be turning on way too often in the summer.

This is why it’s a good idea to adjust the humidity setting twice a year.

What Are The Different Types of Bathroom Fans?

Multiple types of bathroom exhaust fans could be installed in your bathroom, or to choose from when updating.

1. Ceiling-Mounted Exhaust Fans

These fans are intended for upstairs bathrooms to ensure good airflow through these higher-level bathrooms. They are mounted to the ceiling of the bathroom, as the name suggests, and pushes air outside through a hole in the ceiling.

2. Wall-Mounted Exhaust Fans

This type is intended for bathrooms with an outside facing wall. It makes for quicker and easier installation than many others and just allows fresh air in and stale air out.

3. Exterior Exhaust Fans

Like wall-mounted fans, this pushes the stale air out and allows the fresh air into the bathroom on an outside-facing wall. However, this one is often less noisy than the others as it doesn’t have the loud fan sounds. The only sounds that you’d be hearing would be coming from whatever is going on outside the room.

4. Inline fans

These fans are instilled into either the ceiling or the wall, depending on need. The motor, however, sits between ducts to pull the air outside. This fan is also incredibly quiet compared to the others as the motor is at a distance and not connected directly to the ceiling.

What Are Common Bathroom Fan Problems?

There are more problems for bathroom fans than it just turning on or off on its own.

1. Noisy Fan

Both the blades and the motors on bathroom fans can wear out after constant use throughout their lifetime. Once they’ve begun to wear out, they become quite loud while you use them, and that is a good sign that it needs to be replaced.

Here I have a list of 8 super quiet bathroom fans. They are truly the quietest on the market today and I will keep this list updated.

It’s as simple as just swapping out the old fan or motor with a new one, and it doesn’t need to damage your ceiling in the process.

2. Leaky Vent Causing Mold

This problem only happens if the ducts are not connected to the vent hood properly or does not have the correct pieces to function effectively. A leaky vent can cause visible mold in the area of the leakage, and the best way to solve this problem is to replace outright the duct or vent that is causing the leak.

3. The Fan Has No Suction

This problem is most commonly caused by an old fan or a blocked exhaust. You can test the fan’s suction by placing a piece of toilet paper against the exterior of the fan; if it does not hold, then you need to replace the old fan or solve the blocked exhaust.

4. The Exhaust Vent Not Getting Outside

If this is a problem you are having, your vent is not up to code and needs to be fixed. It is required that an exhaust vent is discharging the air outside, and not into another enclosed space. If this is not happening, then it can cause severe mold issues inside the home, but it could allow gases from the room the vent ends into the bathroom.

If you are not confident about fixing any of these issues on your own, you should contact a professional. Some of these problems can cause much more severe and prolonged issues in the home and need to be fixed to ensure that your fan is up to code and properly ventilating your bathroom.

Do You Need a Bathroom Exhaust Fan?

Yes. Bathroom exhaust fans are absolutely essential to all bathrooms. Showers and baths cause a lot of moisture in the way of steam that gathers all over the crevasses of your walls. Once this moisture accumulates and has nowhere to go, it will start causing severe issues in your bathroom.


Your bathroom exhaust fan plays an incredibly critical role in your bathroom to reduce the amount of humidity in the room. If the moisture is trapped in the room, it will start to cause the paint to peel, wallpaper to come off, and even start causing wood in the room to warp.

However, the worst and most significant damage caused by humidity buildup is the growth of mold in the bathroom. Mold is incredibly difficult to get rid of, but so much easier to avoid if the room is properly ventilated.


The ventilation that is offered by exhaust fan can help draw out any unpleasant odors that can accumulate in a bathroom. Exhaust fans can not only help maintain a clean bathroom but also avoid trapping unpleasant odors inside.

Foggy Mirrors

Though hardly the most crucial role of an exhaust fan, this can be important for convenience’s sake after a nice hot shower. The moisture created by the steam of a shower can accumulate on the mirror and walls but is easily drawn out by the exhaust fan.

Airborne Contaminants

Trapping any contaminants in a room is incredibly ill-advised, and bathrooms have some of the worst. Even when cleaning a bathroom, the chemicals used to clean a bathroom are often incredibly harsh and are not meant to be breathed in. An exhaust fan can draw these chemicals and other contaminants out of the bathroom for easy and safe breathing inside the enclosed space.

It only takes 24 to 48 hours for mold to begin to germinate and grow on average. Though, they only become visible after 18 to 21 days on average, even though they colonize much earlier than that. Mold removal takes anywhere from 1 to 5 days but breathing in excessive amounts of mold before you can get it removed can cause severe allergic reactions and respiratory issues.

This is one of the main reasons it is so essential to ensure that your bathroom is properly ventilated and not grow mold because of trapped moisture. Keep in mind that preventing the growth of mold is much easier than dealing with it once it’s grown.

There are multiple different types of bathroom exhaust fans intended for different rooms, all with the same goal of properly ventilating the room. If an exhaust fan is faulty, it can lead to much more serious and damaging issues in the future, such as the growth of mold in the bathroom or attic.

Any faulty piece of your bathroom exhaust fan, such as a humidity sensor or a timer that has become defective, should be taken seriously and replaced right away. Dealing with the defective piece early can help avoid the growth of mold, and help keep your bathroom clean and nice throughout its lifetime.

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