What Does A Bathroom Exhaust Fan do?

During the older days, bathrooms only had one small window. But nowadays, exhaust fans are an important part of bathrooms, and it’s impossible to imagine one without an exhaust fan. But what is the purpose of this exhaust fan, and what does it do? 

Exhaust fans in the bathroom can benefit in multiple ways. The bathroom exhaust fans will improve the air quality, control smell, and humidity, prevent the wall paints from decaying, and stop mold formation. The exhaust fan also circulates air and makes you feel fresh and cool. 

Installing a bathroom exhaust can take time, but it is worth the time and effort as it eliminates hot moist air and bad odors. In this article, we will discuss the functions of the exhaust fans in the bathroom, how it works, and things to consider while choosing one. 

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How does a bathroom exhaust fan work?

A normal bathroom contains a sink, light fixtures, vanity, mirror, faucet, shower, and an exhaust fan. 

Having an exhaust fan may feel fashionable and nice, but that is not the only purpose of adding an exhaust fan. It has way more benefits. 

It helps to keep the bathroom clean and hygienic. 

These exhaust fans are connected and wired to your house’s electrical current, just like a light fixture. 

When you turn on your wall switch, the fan will start working after some time. 

The bathroom exhaust fan will start moving the interior air out of the bathroom through a vent duct or a flexible tube to the outside. 

The vent duct will then transfer the air through the roof or an exit vent on the sidewall of your house. 

The duct will remain closed through the cover plate on the vent’s exit when you do not need to use it. 

Maximum building codes will recommend installing a bathroom exhaust fan for new house constructions or remodeling. 

In California, exhaust fans with humidity and motion sensors are mandatory for the bathroom under title 24. 

These exhaust fans will operate when the humidity level is too much or it meets a sensor notes motion. 

These features must pass the inspection, and the installation and other aspects must meet the building code requirements. 

The fan size will depend on your bathroom’s square footage so that it can give adequate ventilation. 

Even if your building codes do not speak about the compulsory addition of exhaust fans, having one can improve the air quality and benefit in multiple ways. 

What does a bathroom exhaust fan do?

As I said, bathrooms used to have only open windows in the old days, which was enough. But not anymore. 

Without an exhaust fan, your bathroom will face several difficulties. Exhaust fans can help in many ways. 

In this section, we shall learn what an exhaust fan can do for your bathroom:

Humidity and mold control

Humidity is a very common problem in bathrooms. 

It does not matter whether you take a hot shower daily or occasionally because the humidity is always natural and a problem in the bathroom. 

If the humidity level gets uncontrollable, your bathroom will develop mold and mildew in no time. 

Mold can develop several health issues. It is very dangerous for people with allergies.

Once your bathroom starts developing mold, it will start growing rapidly in no time. 

Exhaust fans can control the humidity and mold development in the bathroom. 

Exhaust fans’ introductory job is to control the humidity level of the bathroom. 

The quality of your bathroom exhaust fan will control the humidity and stop mold from developing. 

Once you install a good-quality exhaust fan in the bathroom, you can see what it can do. 

You will not see any fog on the mirror or humidity in the bathroom. 

Odor control

You will try to control your bathroom’s odor by cleaning it daily and spraying multiple odor sprays. 

But you can only control the smell fully if you install an exhaust fan. 

The bathroom will have a very disgusting smell due to the frequent use of toilets. 

An exhaust fan can control and help escape this smell from the bathroom. 

But without the fan, you won’t be able to get rid of it despite frequent cleaning and odor spray. 

If you have properly installed an exhaust fan, the next person visiting the bathroom will have a better experience. 

Fumes removal

When you clean the bathroom, you might use cleaners that contain several dangerous chemicals. 

Inhaling these chemicals can harm your health and badly affect children, old people, and lung patients. 

An exhaust fan will help escape the fumes and smell of these chemicals and keep your bathroom safe. 

Modern exhaust fans contain various good features like humidity sensors, adjustable timings, lights, etc., which can ensure more bathroom safety. 

Gives comfort

During the summer, a bathroom is one of the hottest spaces in the house. 

Exhaust fans will help circulate the air in your bathroom and keep your bathroom comfortable. 

It will release the hot air, bring in fresh and cool air, and make the space comfortable. 

Keeps the wall paints in place

When the humidity level of the bathroom increases, it not only encourages mold but also decays the bathroom’s paint.

Over time, the paint starts peeling off the bathroom’s wall. 

If you do not care about it, the increased moisture level will damage the tiles, tubs, floors, etc. 

It indicates an early replacement of insulation and structure underneath and unnecessary expenses. 

Installing an exhaust fan will keep the humidity in control and reduce the moisture level. 

It will further help keep your bathroom’s wall paint in place and other things in good condition. 


Peeling of the paint and decay in the wall surfaces of the bathrooms will make your bathroom look unattractive and give you a feeling of disgust. 

Installing an exhaust fan in the bathroom can control the humidity and moisture level. 

So it will keep the paint, insulation, and wall designs in place. It means the exhaust fan will maintain the aesthetics of the bathroom. 


A hot shower can make the bathroom mirrors and windows hazy due to the increased humidity and hot air. 

When you are in a hurry, fogged-up mirrors are an issue. 

Exhaust fans can reduce the humidity, clear the air in the bathroom faster and quite efficiently, and you can get a clean mirror every time. 

Illuminates the bathroom 

Most of the exhaust fans in recent days come with additional light fixtures. 

The lighted exhaust fans will offer better ventilation and give you extra illumination in your bathroom. 

As a result, you do not have to add extra light fixtures to your bathroom.  

The design of these modern exhaust fans will offer a stylish and functional bathroom, maintaining the aesthetics. 

What to look for in a bathroom exhaust fan?

There are various types of bathroom exhaust fans available in the market. 

You can get them with multiple styles and features to suit your house’s aesthetic. 

Some exhaust fans have sensors that turn on the fan when the fan detects humidity levels. 

Some fans have timers that shut off the fan automatically once the extra humidity has escaped. 

You can also find exhaust fans with light fixtures, heat lamps, Bluetooth, and speakers. 

But along with these, you must choose exhaust fans depending on your needs, like performance, durability, and safety. 

If the exhaust fan does not work, there is no point in adding one in the bathroom. 


While buying and installing an exhaust fan in the bathroom, make sure it fits according to your bathroom’s square footage. 

You cannot depend on the exhaust fan’s size to understand its ability. 

You must read the manufacturer’s recommendations on the label to understand the capacity.

It would be best not to go too far while selecting the exhaust fan capacity. 

If you select an exhaust fan with high capacity, it will create negative pressure and affect the air circulation and furnace ducts. 

So, you must choose the fan according to the size of your bathroom. 

Noise control

Loud noises are too annoying. 

Sometimes, the bathroom exhaust will create irritating and loud noises, especially in houses with many occupants.

Get fans with fewer noises. Check out the label’s product description and consult the seller before buying one. 

Check the customers’ reviews to gather ideas about how it reacts to daily operation. 


The exhaust fan you get for your bathroom has to be durable because you don’t want to spend money frequently on it.

A good quality and long-lasting fan will prevent humidity and mold formation in the bathroom efficiently in the long run. 

Durable fans will be made of high-quality materials for a longer lifespan and backed up with a warranty. 

Review the installation needs and customers’ points of view to ensure the model’s capacity. 


You will connect the exhaust fans to the electrical system of your house. So, safety is crucial. 

The fan will operate in a space with lots of water and moisture. 

So, be careful about its safety. 

To determine the fan’s safety, look for models having ETL (Electronic Testing Laboratories) and UL (Underwriting Laboratories) certifications. 

Products with these certifications will be a standard ones with good safety measures. 

Once you have installed the fan, run it once during or after the shower to check its functionality. 

If the fan works properly, it will keep your bathroom free of excess moisture and humidity and smell fresh. 

When should you turn on the exhaust fan?

The right time to turn on the bathroom exhaust fan is every time you shower. 

After that, you must leave the fan switched on for at least 15 to 20 minutes after showering. 

Keeping the exhaust fan on for some time will free your bathroom from moisture, mold, and foggy mirror. 

If you do not use the fan properly, the steamy shower can damage the bathroom’s wall and plumbing due to increased moisture levels and mold. 

The paint will start peeling off the wall, the wood will start rotting, and the drywall will become soft. 

How to choose the right exhaust fan for your bathroom?

Based on your bathroom’s configuration, you can choose any one of the standard types of exhaust fans from the following:

  • Ceiling mount: One of the most common types of exhaust fan for the bathroom that exhausts through the duct in the attic to the vent outlet mounted on the rooftop.
  • Inline exhaust fan: The fan is installed in a remote area, for instance, the attic, and connects to the intake duct terminating in a grille on the bathroom ceiling. 
  • Wall-mount or window-mount fan: You can mount this fan if your bathroom has any exterior walls, eliminating the need for long ducts. You can install it in the window just like in the air conditioner. 

What size of exhaust fan will be suitable for the bathroom?

The Home Ventilation Institute or HVI suggests a ventilation rate of 8 air exchanges per hour for the bathrooms. 

The exhaust fan capacity is measured in cubic feet per minute of CFM. 

It has a 1:1 relationship with the bathroom’s square footage, up to 100 square feet. 

A 70 square feet bathroom will need an exhaust fan with 70 CFM, and a 50 square feet bathroom will need a 50 CFM exhaust fan. 

The minimum exhaust fan size must be at least 50 CFM. That is the smallest one available. 

Bathrooms bigger than 100 square feet will need an exhaust fan with more CFMs. 

The HVI recommends the following exhaust fan capacity for the bathroom with multiple occupants:

  • 50 CFM per toilet
  • 50 CFM for a shower
  • 50 CFM for regular bathtub
  • 100 CFM for a jetted bathtub

If you choose an exhaust fan smaller than the bathroom’s square footage, the bathroom will not be properly ventilated. 

So, it cannot control the humidity or improve the air quality. 

An oversized exhaust fan is fine, but make sure the exhaust is not with very high capacity. 

Otherwise, that can have negative pressure on the bathroom. 

You can choose an oversized exhaust fan if the ceiling is above 8 feet. 

Also read: What Type Of Ducting For Bathroom Fan?

Is an opening window better or an exhaust fan?

An open window stands nowhere beside an exhaust fan. 

Suppose you keep a window open during the rain. In that case, it will simply increase the moisture and humidity level of the bathroom, therefore encouraging mold and mildew. 

On the contrary, an open window will increase the energy bill when you keep it open during the cold. 

The cold air will enter your room through the bathroom window, for which you have to increase the heater of your house and end up with high energy bills. 

Though having an open window is wonderful as you can look at the outside nature, you won’t have the courage to open it most of the time. 

So, an exhaust fan is way better than an open window. 

Final thoughts

Bathroom exhaust fans are an integral part of the bathroom, especially in recent times. It helps prevent high humidity, moisture levels, and mold. It controls odor and fumes from different chemicals and supports good air circulation. 

It further helps keep the paint of the bathroom’s wall intact and maintains its aesthetics. While choosing the right exhaust fan for your bathroom, consider certain factors, like performance, noise control, durability, and safety. 

You must also consider the size. The exhaust fan’s size should fit with the square footage of your bathroom. The right time to run the exhaust fan is when you start a shower and switch it off at least 15 to 20 minutes after showering. It will reduce moisture, mold, and foggy mirrors. 

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Arthur Smith

Howdy! I am Arthur Smith, an electrical engineer who is extremely passionate about electronics. I have lived in different parts of the US and currently reside in Wisconsin. I am one of those rare children who knew what he wanted to study and do in life right from the start. I was a curious child who wanted to know how switches work and how the AC works, and I would always observe my dad whenever he would handle the wires and fix things around the house. I currently work as an electrical engineer at a reputed company and write for this blog. And I read loads of books or play video games in my free time.

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