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Is It Safe To Leave A Bathroom Fan On All Night?

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Bathroom fans are great for removing odor and moisture. Safety, however, should always be the main goal when operating an electrical device, because knowing when and how long to operate one is important for preventing a possible fire.


Is it safe to leave a bathroom fan on all night? Experts agree that you should not leave your bathroom fan on all night. You should only run the fan for about 20 minutes during and after a bath or shower. You especially shouldn’t leave it on at night. If it’s run too long, it can cause serious problems and become a fire hazard.

Continue reading to discover all the reasons you shouldn’t leave your bathroom running continuously.

What Is A Bathroom Exhaust Fan Used For?

Bathroom fans are used to create an air flow while using (or after) the shower or taking a bath. They remove the heat and moisture given off by the running water before it can lead to:

  • Mold
  • Structural decay
  • Headaches and an increase in allergy symptom

Can Leaving A Bathroom Fan On Cause A Fire?

While you might think it is okay to let a bathroom fan run 24/7, the truth is that doing so can potentially cause a fire.

tweet about a bathroom fan fire

In 2017, the U. S. Consumer Products Safety Commission (CPSC) did an assessment on exhaust fan fires.

They said, “Staff searched the CPSC Injury or Potential Injury Incident (IPII) database for incidents involving exhaust fans for the 20-year period from January 1, 1997 to September 21, 2017. Staff identified 494 known incidents in that period related to permanently installed exhaust fans. The majority of these incidents occurred in residential bathrooms.”

The results of this assessment pointed strongly toward exhaust fans as the culprit in causing fires.

More than 75 percent (318/423) of the known incidents occurred in a bathroom or restroom. The most likely origin of the incident in these cases was the exhaust fan. The incidents ranged in severity from minor smoke to fire spreading through the structure. Of the 318 incidents that occurred in a bathroom or restroom, almost 80 percent (254/318) occurred in a residence.

Consumer Product Safety Commission

If that doesn’t convince you, maybe this tweet will:

Tweet about a London area bathroom fan fire

This video from television station, Fox59, definitely should:

Bathroom exhaust fan fires can end up costing you big time.

The Westerville Division of Fire in Central Ohio has dealt with several bathroom exhaust fan fires over the years.

In fact, between 2008 and 2015, they responded to 10 fires caused by these fans. “In six of those cases, the fire caused more than $30,000 in damage,” according to the Columbus Dispatch.

tweet about dog saving owner from bathroom fan fire

There are a couple of reasons for why a bathroom exhaust fan could start a fire:

  1. Failing to clean the fan
  2. Faulty wiring

Failing To Clean The Fan

First, if your fan continues to run nonstop, you are sucking in tons of things that can get trapped in the fan when its operating. These include:

  • Dust
  • Dirt
  • Hair
  • Tiny insects

Over time, a build-up of this material can ultimately combust and lead to a fire.

The material could also stop up the motor or keep the fan blades from turning, which means your fan is useless anyway.

This picture of a dirty computer fan gives you a visual of how dust and dirt can stop a fan:

dirty computer fan

Similarly, if your fan or wiring is faulty, or if the fan is old and the insulation around the wires has broken down, your bathroom fan could cause a fire.

The Countryside Fire Protection District in Vernon Hills, IL reported that, “These fans are not designed to last forever and many are original installs. Older exhaust fans are not thermally protected. Thermal protection causes the motor to shut off should they seize and overheat.”

They continued, “This safety feature has been available since the late 1970’s, but was not widely used until the early 1990’s. If you have a bathroom exhaust fan in your home, clean it twice a year. If it starts to make noises or smells odd, it’s time to replace it.”

Faulty Wiring

Another danger of a continually running exhaust fan is defective wiring.

When wires begin to short or malfunction, they can melt, leading to trouble inside the wall of your home. If you smell plastic burning or hear wires sparking when your fan is in operation, turn it off immediately.

Also, if your home is older or is a fixer upper, you might want to contact an electrician if you think there could be trouble with the wiring.


Though it seems redundant to say this, the above problems wouldn’t be an issue if the fan wasn’t overused.

How Do You Clean A Bathroom Fan?

The Countryside Fire Protection District recommends cleaning a bathroom exhaust fan twice a year. To do this, they suggest you:

  1. Inspect and clean all bathroom exhaust fans as necessary and per the manufacturer’s recommendations, be sure to place on a regular cleaning schedule.
  2. When cleaning, remove the fan cover to clean and remove lint from around the motor, paying careful attention to all air-flow areas.
  3. Wash the fan cover in warm soapy water to remove all lint. If there is any mold growing, add bleach to the cleaning mixture. Make sure the cover is completely dry before putting it back up.
  4. If some fans are not easily accessible for regular cleaning, or appear to have evidence of heat damage, or do not turn freely, they should be replaced with thermally protected units.

When To Use A Bathroom Fan

As we’ve been saying, the fan should only run while you are in, or immediately after a bath or shower.

Using the fan to remove smelly bathroom odors is an option, but the main purpose of these fans is to process the large amounts of warmth and moisture that occur during a shower or bath.

How Long Should You Leave Your Bathroom Fan On?

According to Durham Electrical Services in Durham, NC, “You should run the fan for about 20 minutes during and after a bath or shower. That will help the fan fulfill its intended purpose of controlling moisture in your bathroom. You should not, however, leave the fan on 24/7.

Again, running the fan for too long could cause it to malfunction causing problems inside your bathroom ceiling and walls.

Bathroom Fan Timer Switch Can Turn It Off Automatically

exhaust fan

Sometimes it’s easy to forget that the bathroom fan is on. We often just walk out of a bathroom when we’re done using it and might not hear it from another room.

That’s why we recommend having a timer installed.

A timer like the ENERLITES HET06-R-2PCS Countdown Timer Switch will automatically shut your fan off after a programmed time. That way, you don’t have to remember to do it, because it’s taken care of for you.

I actually have the Enerlites bathroom fan timer installed in my own house.

What I like about it is that I have several preset choices (and a reset button) for how long I want the timer to run, plus it has a night-light feature that helps me find the light switch in the dark.

How Often Should You Replace Your Bathroom Fan?

Like the other appliances in your home, the bathroom exhaust fan will reach the end of its days. How will you know when it is time to get a new one?

Here are the four main things to look for when you think your exhaust fan has ceased to function:

  1. Strange noises
  2. Slow performance
  3. No performance
  4. Bathroom renovations

Let’s look at these a little more in-depth:

Strange Noises

If there are weird, odd, or unusual sounds emitting from the fan when it is powered on, you should replace it.

That said, exhaust fans can be loud and will make noise. What you are looking for are noises out of the ordinary that could mean:

  • Engine failure
  • Bearing lockage
  • Fan impingement

Slow Performance

Another way to determine if the exhaust fan needs replacing is a slow start up. When things clog the rotor on the fan, it takes longer for it to spin up to speed.

If the fan is slow to get up to speed when you flip the switch, it might be time to replace it.

No Performance

If you flip the fan’s switch and nothing happens, it’s time to replace your fan.

I know it sounds like a joke to say this because that should be obvious, but nonworking fans need replacing and people often go years without doing it – thinking that it’s not a problem.

The occupants stated that the exhaust fan had “stopped” working about 3 years before the incident. Before the fan “stopped” working, the occupants reported that the exhaust fan had begun to make a noise. Before leaving the home, the occupant went around turning off the lights in the home, which they thought the second floor bathroom fan had been turned off. When they returned home in the evening, the homeowner found smoke coming from the roof vents of the structure. The fan had overheated and ignited and spread into the attic of the structure.

Consumer Product Safety Commission

If the fan still doesn’t work after you check to be that power is still running to the switch, you definitely need a new fan.

Bathroom Renovations

A renovation that adds square footage to an existing bathroom should also require an upgrade in fans.

As I noted in the section on exhaust fan size needs (above), a larger space needs a stronger motor in order to effectively remove moisture in the air following a bath or shower.

What Size Exhaust Fan Do I Need?

Since the main purpose of the fan is to remove moist air from the bathroom area, the general rule for the size of fan you need is: one cubic foot per minute (CFM) per foot. So, in the case of an exhaust fan, the CFM is the rate that it can remove a cubic foot of air in one minute.

That means that if your bathroom is 7’ x 10’ x 8′, you need a fan capable of moving 560 CFM.

Do You Need An Electrician To Replace A Bathroom Fan?

For more intricate jobs like this, it is imperative that you hire an electrician. Working with moisture and electricity is best left to the professionals.

You will need a top-notch electrician for installing a bathroom exhaust fan as any electrical work in bathrooms is considered high risk due to the humid conditions and presence of water.

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