Trade account
How does a bathroom extractor fan work?
Room planning

How does a bathroom extractor fan work?

Posted by Rebecca Doody in Room planning | 1 year ago 6 min read

An extractor fan is one of those things that is kinda just there. It does its job and you don't think any more of it. But have you ever wondered how this mythical piece of technology works? Read on... we've got the answers.


You're in the bathroom. You stare up at the ceiling. You spy the extractor fan. You start to wonder... what does it actually do?! In the essence of helping customers broaden their knowledge, we've answered all your random burning questions. How does it work? Where does all the air end up? What airflow is needed? We've got you covered.

Xpelair simply silent timer bathroom extractor fan

What is a bathroom exhaust fan for?

Perhaps the most important concept we need to address is what the purpose of the bathroom extractor fan is. You can probably guess that the main reason it is there is to get rid of the unwanted smells in your bathroom. Any foul smells can easily be eliminated with the help of an exhaust fan, provided that it is placed strategically.

This will ensure that your bathroom remains hygienic and pleasant. Maintaining good airflow in your bathroom with an extractor fan installed is key for good bathroom ventilation. You might choose to opt for bathroom fans on the bathroom ceiling, and bathroom exhaust fans work just as well as other bathroom ventilation systems, but things like fan noise and what size bathroom exhaust fan to get may be things which stop you in your tracks.

Keeping the humidity in your bathroom at bay is essential for bathroom upkeep. Not only will too much moisture cause the wallpaper and paint to start peeling, but it can also cause mould to form. Without an exhaust fan to control the humidity levels in your bathroom, the spores can multiply at a very quick rate and make it extremely hard to get rid of. A humidity sensor coupled with proper ventilation, or at least adequate ventilation will be very useful, especially since bathroom fans work well the smaller the square foot of a room. In addition, an openable window can help reduce excessive moisture, allowing more air to circulate through the room, ridding the environment of unpleasant smells and excessive mould growth.

An additional benefit of having an extractor fan in your bathroom is that it prevents foggy mirrors. Nobody likes having to wipe off the fog when they are looking at themselves in the mirror, and having a fan to regulate the moisture and eliminate water vapour from your bathroom walls and mirrors.

How does a bathroom extractor fan work?

Bathroom extractor fans are powered by electricity. Inside the fan, an electric current passes through the motor which then converts the electrical energy into kinetic energy that causes the fan to spin. The spinning fan absorbs the moist air inside the bathroom and releases it out of the building through an insulated duct.

Xpelair bathroom timer fan

What is needed for a bathroom extractor fan to operate efficiently?

There are several requirements that need to be met in order for a bathroom exhaust fan to function at an optimum level:

  • The moist air from the bathroom needs to be vented out of the building
  • The airflow of the fresh air (measured in cubic feet per minute or CFM) must be correct
  • The air duct must be large enough and well-made
  • In most cases, the air duct must be fully insulated to prevent condensation occurring
  • There has to be adequate makeup air

Is CFM important?

As a rule of thumb, the bigger your bathroom is, the bigger your extractor fan should be. This is because the recommended number of air changes for any bathroom is 8 per hour. Most of the time, a bathroom exhaust fan is connected to an air duct.

Some things to take note of about the air duct is that you have to ensure that it is as straight and short as possible and that it is adequately sized. Always remember: there is no problem with air ducts that are too big, but an air duct that is too small will waste electricity and make the fan unnecessarily loud.

Where does the exhausted air go?

What most new homeowners may not know is that a bathroom fan must always be directed outside. In fact, this is a building requirement almost everywhere in the world, and even if the building code in your area does not require you to do so, we strongly recommend that you do. When moving into a new place, you should always ensure that the exhausted air gets directed outside to prevent damage to your home which will be very expensive to repair. 

You can check this yourself or opt for a building inspector to check it for you. This is important because sometimes, Tradespeople direct the exhaust vents into the attic as it is much easier and quicker. This should not be the case because, in an enclosed space, the moist air will condense on the cold surfaces and result in mould and damage to walls and other surfaces. On top of this, redirecting the air outside prevents foul smells from being circulated throughout the rest of the house and will in turn improve the indoor air quality (IAQ).

Orchard 6mm two door quadrant shower enclosure

Why does the exhausted air need to be vented outside?

Your Tradesperson may have attempted to save some money by venting your bathroom fan into your attic or elsewhere in the house. However, this may end up costing you thousands in repair costs and might even be worse than having no ventilation at all.

Here are a few reasons why the exhausted air cannot be vented in the house:

Redirecting the exhausted air into the crawl space under your house is not a good idea because, in the winter, the cold humid air that is redirected into the crawl space will condensate on the metal and wood, causing them to rust and rot. On top of this, mould will start growing in the crawl space in no time. With the wood, metal and mould, you will be looking at a pretty hefty bill for all the repairs.

Venting the air into the attic is also not recommended as it will saturate the insulation. This will decrease the R-value (how well something insulates) greatly and result in high electricity bills.

How do I know if the exhausted air goes outside?

An effective and inexpensive way to test if your bathroom extractor fan redirects the air outside is by using a fog machine. All you have to do is place the fog machine next to the exhaust fan and have someone on the outside see if the fog is redirected out of the house (don’t worry, the fog is harmless and is often used in concerts and parties). If there is no steam coming out of the house, it means that the exhaust fan terminates somewhere inside the house. This is also a great way to check for any leaks in your venting system.

Orchard L shaped left handed shower bath

Are bathroom extractor fans necessary?

As long as your bathroom has a window that can be opened, an extractor fan isn't a necessary requirement, according to building regulations. However, in most new-build properties, an extractor fan is a prerequisite. Whatever your bathroom situation, an extractor fan will help you avoid the issues that mould and damp can cause.


Extractor fans play a key role in ensuring that your bathroom is clean and odour-free. Now that you know the do’s and don'ts of bathroom exhaust fans, make sure that the one you choose meets all the necessary requirements.

Keep your bathroom and home clean and healthy

Taking all of the above into account, take a look at our fantastic range of extractor fans. We have something to suit every home, with a variety of sizes, speeds and features available to ventilate your home and reduce the chances of mould and damp forming.

Shop bathroom extractor fans

Author, Rebecca Doody

Posted by Rebecca Doody in Room planning | 1 year ago

Originally from Somerset, Rebecca is our resident copywriter who takes care of all things product related. Rebecca loves the modern interior style with both neutral and bold influences to create a statement look.

Sales Line 0344 264 4141 Track order Design Service Trade account

Looks like you haven't added anything to compare yet

Just look out for the Add to compare around the site and revisit this link

Close and continue

Thank you for using our comparison feature.

You can add as many products as you like, there is no limit. When you’re ready simply visit this page to start comparing your products.

Close and continue

Loading menu. Please wait


Your Shopping list is loading, this shouldn't take long.

Your basket is loading, this shouldn't take long.