What are Bathroom Fans For: Complete Guide

In almost every bathroom, you will often find two switches: one for the bathroom light switch and the other for the fan. Many homeowners will use the bathroom fan during showering or while going to the restroom. 

However, what are bathroom fans used for, and what is the importance of having them?

The importance of a bathroom exhaust fan is to allow the moisture to get removed out of the bathroom. 

The fan also eliminates odors and unpleasant smells within the vicinity and prevents rust and bacteria growth from occurring. 

This article will describe when you should use a bathroom fan and how it works. It is essential to know why there is a fan there that does not seem to be doing anything, especially if it is not blowing air out. Keep reading for more!

What are Bathroom Fans for?

Any bathroom that does not have proper bathroom ventilation is asking for trouble, which you may already have experienced by now. 

There are two main reasons why you use bathroom fans:

1. Prevents Moisture from Remaining in the Bathroom

As mentioned previously, bathroom vent fans help keep excess moisture off of the walls and help maintain a relatively clean environment. 

Prolonged moisture can cause multiple issues within the home, such as poor indoor air quality, microbial growth on surfaces, rusted fixtured, peeling paint and wallpaper, and warped doors. 

High humidity causes peeling paint which increases the chances for mold and mildew growth in drywall. More often than not, these are within places that you cannot see.

A bath fan that is not ducted correctly, expels humid air into wall cavities or attics where mold growth can go undetected for months or even years. A 4 inch flex duct should run from the fan outlet to the exterior.

This photo shows mold growth on roof decking because the bathroom venting is incorrect

When no attic space is available (such as on a first floor or a house with a flat roof) and ducting is not possible, ventless bathroom fans are available. However, a word of caution, ventless fans have a charcoal filter that has to be replaced, generally every 30 days. If you have attic access, it’s best to install a correctly vented fan.

2. Removes Odor from the Bathroom

Bathrooms are one of the dirtiest places within your home, so it is essential to do everything possible to prevent them from getting too messy. 

In that case, another critical factor to consider is the odor that gets removed from the bathroom fan

Once the fan turns on, fresh air replaces the thick air relatively quickly, leaving the bathroom to become more of a fresh scent.  

So, if you need to go number two, make sure to leave that fan on for roughly 20 minutes.

Without a fan in place, the odor will linger for much longer, so make sure to open a window for a few minutes if that is the case. 

However, suppose you cannot remember to turn off the fan after those few minutes. 

In that case, it may be a wise decision to invest in a timer that allows the fan to turn off automatically. 

How Does a Bathroom Vent Fan Work?

The way bathroom ventilation fans work is relatively straightforward. After the switch turns on, the air gets sent out of the room through a vent duct. The air then empties through the exterior through a wall, soffit, or the roof of your home.

When you are not using the vent fan, a louvered cover plate protects the vent’s exit, ensuring the duct is closed when you are not using it. 

You will typically find the vent cover on the wall’s exterior or top of the roof. 

The surface in itself has a flashed roof cap that is securely locked in place with silicone caulk and four screws. 

In terms of the bath fan wiring, a vent fan may be wired in the same electrical current as other light fixtures are within the home. 

The vent fan has a standard 120-volt electrical current wiring system, which a switch helps to operate. In some cases, a timer may allow the fan to stay on for a specific amount of time continuously. 

How Bath Fans are Sized? 

Bathroom vent fans come in various sizes based on the cubic feet per minute (CFM) of moved air. Therefore the square footage of the bathroom matters. Too small and the fan won’t move enough air to make a difference.

Cubic feet = length x width x height. A bathroom with 9ft length, 6ft wide, and 8ft ceilings whould have 432 ft3.

For example, an energy efficient exhaust fan that operates with 110 CFM are suitable for rooms up to 105 square feet, or approximately a 10.5ft by 10ft room. With 8 ft ceilings, 105 square foot of floor space would have 840 cubic feet. Therefore, you’d need to run a 110CFM fan for about 9 minutes.

Fans with Built-in Heaters

Some bath fans have built-in heaters, which are great in small bathrooms that don’t have a heat source. These built-in heaters are electric heat strips and are not energy-efficient to operate, so avoid running them when it’s not necessary.

Will You Need Two Bathroom Fans?

Larger bathrooms will need a larger fan or multiple fans. If your bathroom has a toilet room (water closet) that closes off from the rest of the bathroom, you’ll need at least two fans. Building codes now require that water closets have their own bath fan.

When Should You Use a Bathroom Fan?

The very best time to run a bathroom fan is right after your shower. Since the bathroom vent fan goes from the fan to your home’s exterior, this is the best option to remove steam within your home.

On the other hand, you can use a bathroom fan when using the restroom. The reason being is because the fan helps to remove the odorous smells after finishing. In that case, it might be best to keep the fan remaining on for a few minutes afterward. 

If you are forgetful, which many of us are, then it is a wise decision to have a timer in your washroom. That way, it is guaranteed to turn off instead of remembering hours later or coming back home to a bath fan running. 

Is a Bathroom Fan & Exhaust Fan the Same?

Bathroom fans are very similar but not quite the same. However, some people will still call them the same. Here are some similar names used for a bathroom fan:

  • Engine cooling system
  • Electric fan
  • Blower
  • Exhaust fan
  • Punkah

So, what is the difference between exhaust and a bathroom fan? It is the way they are both used.

Exhaust Fan

An exhaust fan’s main job is to remove pollen from the air inside a home or commercial space. It mostly gets used in kitchens, bathrooms, and factories. The exhaust fan’s location of operation is near a window or by exhaust hoods. 

Bathroom Fan

As we went over previously, the bathroom fan helps to remove moisture in the air and cleans the air by sucking it out through the ducts into the outdoors. You’ll see these in the restroom or over the oven, and it leads into the outdoors.

Is it Bad to Leave a Bathroom Fan On?

It is not wise to leave a bathroom fan on continuously, especially during the evening. Doing so can lead to a potential fire and other issues at hand. 

We constantly clean out our small fans within our rooms, but what about the bathroom fan? Failing to clean heating units, computer fans, lights, and even oven buffs are also at risk. 

Although these fans are not the number one cause of fires inside homes, a relatively large amount of them still occur. 

The U.S. Consumer Products Safety Commission (CPSC) assessed how many fires started from January 1997 to September 2017. They found out that 494 total fire incidents occurred because of exhaust fans. 

More specifically, 75.18% or 318 out of the 494 fires were known incidents from bathroom vent fans.

So, why did these fires occur in the first place? There are two main reasons:

  • Faulty wiring
  • The fan was full of dust

Dust Inside the Fan

If you have failed to clean your fan, there might be some hair, dust, debris, or even insects living inside them. 

The build-up eventually becomes too much for the fan or vent duct, leading to a safety hazard. Failing to clean it out also means the fan is useless, so there is no point in turning it on. 

Wires Failing on You

An exhaust fan constantly running can lead to the wires failing on you. 

If you smell plastic burning or hear a sparking noise, this can directly result in the wires malfunctioning. Also, you must immediately turn it off, so a fire does not occur. 

Make sure to call an electrician right away if this is the case. Sure, you can keep the fan off, but if you have younger children, they are curious and could potentially flip the switch on without knowing. 

If your home is older, it is also a good decision to contact a professional for your safety, especially if you are first purchasing a home. 

However, for a relatively newer home, make sure not to overuse it, so this issue does not occur. 

Should I Run the Bathroom Fan While Showering?

It is extremely wise to run the bathroom fan on while showering. According to the Home Ventilation Institute (HVI), you should run the exhaust fan for roughly 20 minutes after taking a hot shower.

Suppose you typically like taking hot and steamy showers. In that case, the bathroom will look very foggy once finished, leaving it difficult to see, and you feel the moisture seep into your body. 

Although steam is good while you are sick to help with any phlegm, you should always keep the bathroom exhaust fan on while you shower.

Not only that, but excess moisture can get into the plumbing and walls without the proper ventilation required. Since paint can peel off much quicker, mold can quickly grow in unwanted areas.

Having mold in those areas also means many issues, such as structural damage or rotting wood. 

If the mold growth is too bad, it can grow into other rooms within your home. 

You can keep the bathroom sparkling clean as long as you want. However, an interior issue will allow microorganisms to grow because of excess moisture. 

Not only that, but mold spores are in the air, leaving you and your family becoming more prone to sicknesses and respiratory illnesses.

Do Bathroom Fans Help Cool the Room?

A bath fan can’t cool the room itself. Bathroom fans draw air from inside the room and expels it outside. As the fan spins, it’s pulling the moist air up and out through the ducting.

You might sense a “cooling” temperature drop in the room with a bath fan on, but it’s not because it’s cooling the room. The temperature drop is because the fan is removing hot, humid air from the room.

Should Bathroom Fans Be Vented Outside?

It is required to have a bathroom fan vented to the outdoors. Some fans can go out through the attic, but if that is not the case, you need to make sure the vent is on the side of the home somewhere. 

If your fan gets into an open attic, it can cause moisture to seep in, so make sure you do not vent the fan through a ridge vent or soffit vent.

In some areas, like California, it is required that all exhaust fans in spas or bathrooms with showers and bathtubs must be ENERGY STAR compliant and vented to the outside. 

Do Bathroom Fans Get Rid of Moisture?

Bathroom vents will help get rid of moisture in the room. Suppose you just took a shower and want to look at yourself in the mirror but not create streaks. 

In that case, turn on the bathroom vent and allow it to suck the dampness out of the bathroom. In some cases, the bathroom fan might have already done the job for you. 

Another instance is if you want to make sure mold does not occur inside the bathroom. An exhaust fan can help with this potential hazard. 

Are Bathroom Fans with Humidity Sensors Worth it?

In many cases, people turn off the bathroom fan too quickly before they finish showering, keeping moisture in the washroom much longer than it should be. 

They don’t consider the humidity levels inside the bathroom are still too high. Because humidity sensors control the bathroom’s moisture levels, it is worth purchasing.

In that case, you might be considering getting a fan with a humidity sensor, especially since leaving it on too little can lead to issues in the future. A humidity sensor powers the fan on and off to maintain a preset humidity level of your choosing.

Assume you own rental properties and do not want the renters damaging the area too much. Then humidity sensors come in handy by automatically turning the fan on, especially if the renters forget to do it themselves. 

Should Bathroom Fans be Loud? (Sone Ratings)

Quiet bathroom fans are perferable because they are less distracting, especially if you like to listen to music or watch videos while getting ready for work. Having a noisy bathroom fan can be relatively irritable, especially if you go into a spa or your bathroom is made to be quite relaxing.

Sound level is measured in decibels. However, you won’t see a decibel level on the packaging. What you will want to look at the sone rating for a bathroom fan. 

The higher the rating, the noisier the fan will be. Since you most likely want a quiet sound rating fan, you will want to look into 1.5 or below. The softest bathroom fans are 0.5 sones and down, whereas a loud noise level would be at a 4.0 rating. 

Given that information, it is not required for a bathroom fixture to be loud. The lower the rating, the better and softer sound it is. 

You can find many ratings at a specific sone level, such as the CFM rating, price points, and energy consumption rating. Fans with lower sone ratings are often more expensive.

Make sure to check what the dimensions of that fan unit are before purchasing. The last thing you need is to return an item that is not big or small enough.

Final Thought

Overall, Energy Star rated bathroom fans help remove excessive moisture build-up in the air and costs little to operate. Keeping them around will be extremely handy as time goes on and will save you a ton of money in the future by preventing water damage from occurring. 


Photo of author

Hubert Miles

I've been conducting home inspections for 17 years. I'm a licensed Home Inspector, Certified Master Inspector (CMI), and FHA 203k Consultant. I started HomeInspectionInsider.com to help people better understand the home inspection process and answer questions about homeownership and home maintenance.
DISCLAIMER: The content published on HomeInspectionInsider.com is not professional advice. You should consult with a licensed professional and check local permit requirements before starting any project.
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