So… You’ve decided to buy an extractor fan. The steam in your bathroom or build-up of cooking deposits in your kitchen has gotten too much to bear. But which fan to choose? There are so many, so many manufacturers, so much terminology. Here are four things you need to know about fitting an extractor fan.

What sizes and types are available.

When imagining an extractor fan, most people think of the wall mounted grille type with a fan blade behind, the kind you see in most bathrooms across the land. This is an axial fan, and for most people, this is as far as it goes. It’s a fan, it goes on the wall, right? Not quite, there are more options to consider than that. Fans come in a few different sizes, the most common for domestic use being 4 inch and 6 inch. This is not the size of the front grille, this is the diameter of the fan blade and the spigot that protrudes out the back and therefore the size of the ducting and accessories required to fit.

The next type is the Centrifugal fan, in most cases looking very much like an axial fan, but the inner workings are slightly different. A centrifugal fan works by way of an enclosed impeller, a blade mounted inside a tube or housing, not necessarily at 90 degrees and drags air through the tube because of the vacuum created, a much more powerful system. Some centrifugal fans can operate a duct run of up to fifty metres, very useful if you are extracting from a room in the middle of your house with no external wall.

The final type is the Inline fan, somewhat similar to the centrifugal fan in that the blade is entirely enclosed, but as the blade is mounted at 90 degrees to the motor, it can also be considered an axial fan. Inline fans can sometimes be referred to as ‘mixed flow’ because of the joining of the two types.

Vastly more powerful than the other types, a 4 inch inline fan gives the same extraction rate as a 6 inch axial fan and able to cope with duct runs up to 10 metres depending on the model. This is because it sits in the run of ducting itself therefore allowing no room for the air extracted to escape or travel in any direction other than to the outside world. Mounted either in the ceiling void if space allows, or in a loft space, it may not be the solution for everyone, but if you have room for one, an inline fan is the way to go. Available in 4, 5 6, 8, and even 12 inch, inline fans range from the domestic to the commercial in their applications.

What room the fan is being fitted in

Depending on what room you are extracting from has a huge bearing on what fan you choose. If you are buying one for a kitchen or utility room, will a visit from a building inspector be involved? UK building regulations require a certain rate in litres per second to be extracted from these rooms, 60L/s for a kitchen, 30L/s for a utility room, so you must choose a fan that meets these extraction rates. A 6 inch axial fan will extract around 240 metres cubed per hour, which equates to around 60 litres per second, ideal for both a kitchen and a utility room. A bathroom requires nowhere near that kind of extraction, a mere 15L/s a 4 inch fan will easily cover this. You do however, need to think about bathroom zoning.

What is bathroom zoning?

A bathroom is divided into sections, or zones, to denote how close electrical items will be to water. Zone 1 is basically within the footprint of the bath or shower and up to 2.25 metres high, zone 2 is 60cm outside of that in all directions and then beyond that is zone 3, or ‘no zone’. Fans that need to be fitted in zones 1 or 2 need to be correctly rated in order to be fitted there so as to not blow or, in the worst case, cause electrocution if water gets inside.

To conform to these requirements there are two solutions, low voltage or IP rated. Low voltage, or SELV (Safety Electric Low Voltage) is a system that attaches to a transformer fitted outside of Zone 2 that converts UK mains 240v down to 12v, a voltage that won’t kill you if contact is made. Most electricians will tell you that if fitting a fan in Zone 1 or 2, you must have a low voltage fan. This is not quite true. An IP rated, or ‘Ingress Protection’ rated fan has its electrical contacts inside a water proof casing and, according to the 17th Edition of the regulations, so long as the fan has a rating of IPX5 and is on an RCD protected circuit, it is perfectly acceptable to be fitted in Zone 1 and 2.

How you want your fan to be controlled.

Fans can be switched on in a few different ways, and depending on the room you are fitting it in can decide what you choose. The usual three functionalities for a fan are Basic/ Standard, Timer and Humidistat.

Basic is as it sounds, you turn it on and off as it is required and it does as it is told. That’s it.

A Timer fan, usually attached to a lighting circuit, comes on when you turn on the lights and continues to run while the lights are on. When the lights are turned off, a small device inside kicks in and makes the fan continue to run for the duration set at install, decided by you. From 2 minutes up to as much as half an hour in some cases, depending on your requirements.

A Humidistat fan has a device inbuilt that senses the humidity in the air and triggers the fan when the threshold set at install is exceeded. It will then continue to run until the humidity goes below that threshold. Sometimes coupled with a timer too, a humidistat fan is best in a room where it is not always likely the lights will be turned on, either in a bathroom or kitchen with a large window allowing plebty of natural light, or as a set and forget solution like a utility room when washing machines and tumble dryers run without constant human monitoring. If you are fitting a fan in a room where the lights will always be turned on when using it, a humidistat will be totally unnecessary.

Other functionalities include pullcord which, as the name suggests, is another basic switching option attached to the fan, and PIR (Passive Infra Red) which senses you when you walk into the room, triggering the fan. PIR is a system most useful when human interaction is not trusted to trigger the fan, a true set and forget solution.