How to select a Bathroom Fan

First you need to measure the size of your bathroom. To use our fan selection tool (located in the search area to the right of every page) this measurement needs to be in metres.


Let’s say the length of your bathroom is 3 metres, the width is 2 metres, and the height is 2.8 metres. That would be: 3 x 2 x 2.8 = 16.8 m³ (the volume).


For a bathroom we recommend 10 air change an hour, or a minimum of 54 m³/​hr (15 litres a second). In this example the amount of air that should be extracted from the bathroom is:

  • 16.8 m³ (the area of the bathroom)
  • x 10 air changes an hour
  • = 168 m³/​hr

This is above the minimum we recommend of 54 m³/​hr. So in this example the fan required for a bathroom 3 metres x 2 metres x 2.8 metres is:

  • 168 m³/​hr or 47 litres a second

Most bathroom fan manufacturers publish the fan performance in m3/​hr or litres / second (l/​s)

If you use our fan selection tool a list of fans suitable for your bathroom will be listed. The only things left to consider are

  • Price
  • Design
  • Noise
  • Extra functions e.g. Back Draught Shutters, Run On Timer, Humidity Sensor, Passive Infra-red (PIR) Sensor

Important Note — Building regulations state in a room with no openable window, an intermittent extract fan should be used with a run on facility set to a minimum of 15 minutes.”

We assume this is what the majority of people usually consider – with price being the biggest driver, we would recommend you should consider the following:

  • Noise – no one wants to be relaxing in the bath with a noisy fan running in the background, we would recommend a fan with a noise level no higher than 45dB(A) at 1.5 metres from the listener to maintain comfort.
  • Price – remember most of the time you get what you pay for.
  • Design – you will always find a fan to suit your design requirements – remember that, the chances are, you’ll have to look at this fan for years to come.
  • Environment – Legislation requirements for fans (such as Part F and Part L) now mean bathroom fans are available to suit every environmental need. These include Low carbon and Low voltage as the major options. In the short term the greener you want to be the more you pay. But in the long term the overall cost to you and the planet should be lower.
  • Extra functions – we would suggest this should be your last consideration, and would recommend the minimum you should have is a back draught shutter, the rest is to personal taste. If the fan is being linked to a light switch, and you use the lights every time you use the bathroom, no other extras are required. If not we would only suggest you use a fan fitted with a PIR to ensure it runs every time you enter the bathroom.
  • Note on Extra Functions – If you think Yes, I want my Bathroom extractor fan to have extra functions’, we suggest where possible these are bought as separate items. For example if you want a fan with a humidistat, buy the fan and humidistat as two separate items, the reason? Buying the fan with a built in humidistat will cost a lot more than without, and if the fan or the humidistat becomes faulty (nothing last forever) you’ll need to spend a more money to replace it. If you buy them as separate items, when one becomes faulty you only need to replace that part, thus saving money. 

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