Choosing the Right Extractor Fan

Extractor Fan Purpose

Extractor fans are installed for two main purposes:

  • To remove moisture from the air
  • To remove odors

In terms of functionality, the extractor fan needs to be the right size for the room if it is to do its job properly:

  • If it's too small it won't be able to draw sufficiently enough air
  • If it's too big, it will allow too much hot air out of the room

There are also certain regulations that must be adhered to when installing a ventilation system.

First Things First To select the right size extractor fan, you must calculate the room's required air flow rate:

  • multiply the height, width and length of the room to calculate the volume
  • Then, multiply the volume by the number of air changes required per hour for that room. This will give you a figure in m³/hour. Once you have this figure, you can select the most suitably sized unit.
  • Room Volume X Required Air Changes = m3/Hour Required

According to the Building Regulations 2010 Document F, the following ventilation rates are required for non-inhabitable rooms:

  • Toilet/ Sanitary accommodation 6 l/sec (22 m3/hr)
  • Bathroom/ shower room 15 l/s (54 m3/hr)
  • Kitchen adjacent to hob 30 l/sec (108 m3/hr)
  • Kitchen without cooker hood 60 l/sec (216 m3/hr)
  • Utility room 30 l/sec (108 m3/hr)

Types of Extractor Fan

There are four main types of extractor fans:

  • Axial - Moves air over short distances
  • Centrifugal - Moves air over longer distances
  • Mixed-Flow - Moves more air over longer distances

Axial, centrifugal and mixed-flow fans can be either ceiling mounted, wall mounted or inline mounted (in the loft usually).

Extractor fans can operate in a variety of ways:

  • Standard models are available for remote switching via a wall light or separate switch
  • other models may operate via a timer (with integrated adjustable time delay)
  • via pull cord
  • via a PIR (passive infra-red) sensor which switches the extractor fan on and off when the room is entered or vacated
  • Extractor fans may also operate automatically via integrated humidity control technology.

The choice of fan largely comes down to the room it's to be installed in and customer preference.

Extractor Fan Wiring Regulations

According to the IEE Wiring Regulations, a room containing a bath or a shower is considered to be a special location due to the increased risk of electric shock.

Certain conditions must be met in different zones of the room:

  • a minimum of IPX7 rated appliances must be installed in Zone 0 (inside the bath or shower tray itself)
  • a minimum of IPX5 rated appliances must be used in Zone 1 (above the bath or shower tray)
  • IPX5 is also a requirement for Zone 2 (the area stretching 0.6m outside the perimeter of the bath to a height of 2.25m)
  • A certified electrician is necessary for the installation of additional cabling and isolation point if needed.

Quiet Bathroom Extractor Fans

There are a couple of other points to consider:

When selecting an extractor fan be sure to check its noise level. If you want a particularly quiet extractor fan then choose a unit with a dB level less than 32.

Units with a dB level of 42 or above could be considered noisy. Generally, axial extractor fans are the quietest, whereas centrifugal fans can be quite noisy.

The other thing to think about is the type of exterior grille you will need. There are two main types available: fixed or gravity.

Gravity grilles are usually used as they prevent back draughts, but these grilles shouldn't be used with weak extractor fans as the air won't be strong enough to push open the louvers. Gravity exterior grilles are also not ideal for installation near a bedroom window as they can be noisy when they clatter shut. It's also possible to purchase fans with built-in shutters to remove the need for a gravity grille.

Useful Links Relevant to Extractor Fans:

The Building Regulations 2010 Approved Document
HM Government Domestic Ventilation Compliance Guide:
IEE Wiring Regulations