How to fit an extractor fan


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These tasks may be tricky so will suit you if you're experienced in DIY, or simply love a challenge.

This job requires some electrical wiring skill. If you're unsure, talk to a professional electrician.

Before you get started on any of our 'how to' guides, please take a moment to read through our DIY safety tips.

Tools for the job

1. Installing a fan in a window

  • Measure the window (fig. 1) and get your new piece of glass or double-glazed unit from a glass merchant. Take in a paper plan of the pane showing the exact diameter and position of the hole you want (fig. 1).
  • The fan housing is larger than the hole so leave enough space around the hole for the housing (fig. 1). When fixing a fan in a sash window, the top sash must be sealed shut with screws. Then fit sash stops on each side of the window to stop the fan being damaged when the lower sash is raised (fig. 2).
  • To fix and wire the fan follow the manufacturer's instructions.
Remember to measure to the edge of the glass surround and not the inside edge of the beading.
Figure 1
If you're putting a fan into a sliding sash window, seal the top sash shut and fix sash stops in place. get a qualified glazier
Figure 2

2. Installing a fan in the wall

Positioning the fan
  • Decide the position of your fan. Use a cable finder to check if there are any buried cables or pipes in the wall.
  • Also check your outside wall for obstructions - such as rain, waste or soil pipes - and that the position of your fan won't send fumes into your neighbour's windows.
  • Mark the position and diameter of the hole on the inside wall. See the manufacturer's instructions for details.
Making the hole for the fan in your wall
  • Mark the centre of the hole and drill through the wall at this point with a hammer drill and masonry bit. Angle the drill slightly downwards.
  • Using the drilled hole as a centre point, mark the extractor opening on the outside wall.
  • With a 10mm bit, drill a series of holes at 35mm intervals round the edge of the circle (fig. 3).
  • Next, use a 60mm bolster chisel and club hammer to chop out the waste. Smooth the rough edges with a cold chisel.
  • If necessary, use a chisel and hammer to cut grooves in your internal plasterwork to take the cable and conduit. You'll have to plaster and redecorate afterwards
Fitting the fan
  • Fit aluminium ducting into the hole (fig. 4), flush with both sides of the wall. Ensure the duct slopes slightly downwards towards the outside. Always wear gloves when handling the ducting, as it has sharp edges.
  • Next, tidy up around the duct. Use sand and cement outside, and plaster or filler inside.
  • Follow the manufacturer's instructions to position the fan and mark the fixing holes. If it has a slatted grille front cover, make sure the slats are horizontal. Drill and plug the holes and fix the fan to the wall.
  • Follow a similar process for the outside wall grille.
To start your hole, use a 10mm bit to drill a series of holes at 35mm intervals round the edge of the circle.
Figure 3
Fitting a fan over a bath or shower.
Figure 4

3. Fitting a fan over a bath/shower

Choosing the right fan and getting started
  • Make sure you buy an extractor fan specifically designed for a 'splash zone'. Follow the manufacturer's instructions when positioning the fan. If you're in any doubt, talk to a qualified electrician.
  • Use a 220 volt fan if you're installing it on an internal wall. The wall must be between 275mm and 350mm thick.
  • Alternatively, you can use a 12 volt fan but make sure the transformer is at least 2.5m away from any water source or steam. It can be fitted in a loft space, cupboard or in the same room.
  • Cut a hole through the wall that's the right size for your fan (see 'Installing a fan in a wall' for help).
Positioning the wiring and external ducting for the fan 
  • Cut a groove in the plaster for the power cable, making sure it's in the right place for cable entry (fig. 4). Put the power cable in position, leaving at least 250mm extra cable to spare.
  • After passing the cable through the hole, extend the flexible ducting to the length required (maximum 350mm long). Insert the ducting into the hole and make good with the ducting lying flush on either side of the wall. Don't plaster in the cable at this stage.
  • Fix the outer grille into position. Insert the backdraft shutter (if supplied with your extractor fan) until it touches the outer grille.
  • Wire up your fan according to the manufacturer's instructions.
Fitting the fan chassis
  • Insert the fan into the duct (fig. 4) and make sure there's a minimum of 175mm between the face of the wall and the rear of the fan chassis. Secure the cable into self-adhesive clips and put it in place.
  • Tidy up the cable at the edge of the duct and fit the interior fixed grille.

4. Fitting a fan in the ceiling

Positioning the fan and making the hole in the ceiling
  • Ceiling extractors should be ducted to an outside wall or, if venting into a roof space, by ducting to an external soffit under the eaves or grille in the slope of your roof. Remember that ducting installed between a floor and ceiling can only run between joists, not across them.
  • On the ceiling, mark the position and size of the opening required (see manufacturer's instructions) - make sure it's between the joists.
  • Drill a 9mm hole through the ceiling anywhere on the edge of the circle and then cut out the hole with a plasterboard, utility or pad saw.
Fitting the fan chassis
  • Remove the cover from the fan, hold the fan body against the ceiling and mark the position of the fixing holes. Fix the unit in place using heavy-duty plasterboard fixings.
  • If the fan unit is very heavy or the ceiling a bit fragile, cut a piece of 18mm plywood to fit between the joists. Drill a hole in the centre, 25mm larger than the ceiling hole, then fit the plywood in place with wooden battens and fix the fan unit to it (fig. 5).
  • Hold the ducting in place with metal hose clips. Keep the curves as gentle as possible and stretch the ducting as tight as possible - sharp bends in the ducting will restrict the airflow (fig.6)
If the fan unit is very heavy or the ceiling is fragile, cut a piece of 18mm plywood to fit between the joists.
Figure 5
Keep the curves as gentle as possible and stretch the flexible ducting as tight as possible. This reduces airflow resistance.
Figure 6

5: Electrical installation rules

  • All your wiring must comply with current IEE (Institution of Electrical Engineers) regulations. If you're unsure, get help from a qualified electrician.
  • Make sure all wiring is fixed securely and set in a plastic conduit if it's buried in the wall.
  • The cable to your fan must have 1mm2 to 1.5mm2 section conductors (see the manufacturer's instructions).
  • Fans must be wired via a double pole - switched on both live (L+) and neutral (N-) conductors - and switched fuse spur, having a contact separation of at least 3mm in all poles. It must be fitted with a 3 amp fuse and sited outside any room containing a shower or bath. Make sure you follow the manufacturer's instructions.
  • The fused spur can feed off a ring main or a lighting circuit.
  • Fans supplied by a 0.75mm2 or 1.5mm2 flexible cable can be wired as above or via a plug (fitted with a 3 amp fuse) into a mains socket.
  • Extractor fans, sockets and fixed fused spurs must not be positioned within reach of a person standing at a kitchen sink or hand basin.

6: Switch types and regulations

  • Extractor fans can be operated by a pull switch, a switched fused spur or a light switch.
  • Extractor fans in or adjacent to a shower in a room without a bath can be operated by a light switch, as long as they comply with IEE regulations (fig. 7). Alternatively, they can be controlled by a ceiling pull switch adjacent to the shower.
Helpful hint...

To get the ideal fan you'll need to work out the cubic capacity of the room (width x length x height). You'll also have to know the 'air flow rate' needed: for a bath with no shower allow six to eight times per hour. For a bathroom with a shower allow 15 to 20 times per hour.

Fans in or adjacent to a shower in a room without a fixed bath can be operated by a light switch with IEE regulations
Figure 7

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