How to select a WC Fan

Firstly, you need to measure the size of your W.C. (toilet). To use our fan selection tool (located in the search area to the right) the measurements need to be in metres.


A W.C. for the purposes of this” how to” guide is a room where a toilet and small wash basin is housed.

If this room includes a bath or shower or both please use our how to” bathroom guide.. 


Let’s say the length of your W.C. room is 2 metres long, with a width of 1 metre, and the height is 2.4 metres. That would be: 2 x 1 x 2.4 = 4.8 m³ (the volume).


For a W.C. we recommend 10 air changes an hour, or a minimum of 22 m³ an hour (or 6 litres a second). In this example the amount of air that should be extracted from the Utility Room is:

  • 4.8 m³ (the area of the Utility Room)
  • x 10 air changes an hour
  • = 48 m³/​hr

This is above the minimum we recommend of 22 m³/​hr.
So in this example the fan required for a W.C. 2 metres x 1 metre x 2.4 metres is:

  • 48 m³/​hr or 14 litres a second

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

If you use our fan selection tool a list of fans suitable for your W.C. will be displayed. The only thing 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. With that in mind, we would recommend you should consider the following:

Noise – for a W.C. we would always consider noise first, the last thing we would want when sitting enjoying a good book or the daily newspaper is a loud fan in the background interrupting the calm atmosphere 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

Extra Functions – we would only suggest the use of a backdraught shutter for a W.C. (all the fans in this category on our site include a back draught shutter as standard) it may also be an advantage to wire the fan through the light switch, so when the lights are switched on the fan runs.

Design – you will always find a fan to suit your design requirements, we would suggest this is not as important as the other areas of the house.

Environment – Legislation requirements for fans (such as Part F and Part L) now mean W.C. 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.

Note on Extra functions – If you think yes” I want my W.C. extractor fan to have extra functions, we suggest where possible these are bought a separate items. Buying the fan with a built in function such as a PIR detector will cost a lot more than without, and if the fan or the PIR detector becomes faulty (nothing lasts forever) you’ll need to spend more money to replace it. If you buy them a separate items and one becomes faulty you only need to replace that item, thus saving money.

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