Installation and Connection of Electrical Extractor Fan (Bathroom, WC)

The electrician first decides where the fan should go and where the air will be sent. It can go into a ventilation shaft, into ducting, or straight outside through an external wall. The fan belongs as close as possible to the source of moisture, which means the shower or bath. It still has to stay out of reach of splashing water, and its position must respect the safety zones of the bathroom.

The work itself usually goes like this:

• Marking the position and preparing the opening, usually 100 or 125 mm in diameter depending on the fan and ducting
• Running the cable: in a new build there is usually a ready connection point, in a renovation a channel often has to be cut and a back box fitted
• Mounting the fan body, ideally with a damping gasket against vibration, and sealing the joint with the duct
• Connecting the wires according to the fan type and the manufacturer's instructions
• Setting the overrun time or sensor sensitivity and doing a test run

At the end the cable channels are filled so the wall can be painted or tiled. If you are also getting a new light, it makes sense to do both at once. The light and the fan often share the same cable route.

The type of fan decides how it is wired and how convenient it is in daily use.

• A basic fan with a switch is turned on and off by hand. It suits a WC or utility room where little steam is produced.
• A fan with a timer usually comes on with the light. After you switch the light off, it keeps running for a few minutes, roughly 3 to 15 depending on the setting. In a WC this is a common and practical solution.
• A fan with a humidity sensor starts by itself when humidity rises above a set level and switches off once the room has dried. For a bathroom without a window it is usually a sensible choice.

How powerful should the fan be? Airflow is given in m³/h. A WC usually needs less, a bathroom with a shower needs more. The length of the ducting and the number of bends also matter. With a longer run or several bends, a fan that can build up more pressure is worth considering. Otherwise it will hum away but move very little air. If the bathroom is next to a bedroom, check the noise level stated by the manufacturer as well.

In a block of flats with a shared shaft, a backdraught shutter (non-return flap) is important. It stops air and smells from the shaft flowing back into your flat.

The quickest job is swapping an old fan for a new one of the same type, with a working cable connection and opening already in place. Fitting a completely new fan in a finished bathroom takes more work. The cable has to be run, channels cut into tiles or plaster, and sometimes a new hole drilled.

These things also add to the effort:

• A fan with a timer or sensor, which needs more wires and setting up
• No existing cable connection, or a back box in an awkward place
• Drilling through a thick or insulated external wall
• Mounting on a high ceiling or into a suspended ceiling
• Longer ducting with bends that has to be added

If you live in a block of flats and want a new opening in the façade or to work on a shared shaft, speak to the building management or owners' association first. Some older shafts are designed only for natural ventilation. For changes to the façade, check with your local building authority what the local building regulations require.

As far as electricity goes, the bathroom is one of the riskiest rooms in the home. Water, steam and metal taps combined with a badly connected appliance can cause a serious injury. Work on the electrical installation should therefore be done by a qualified electrician. That is why there is deliberately no DIY guide here. In some countries electrical work in bathrooms also has to be notified or certified, and a qualified electrician will know how this works locally.

The electrician checks that the bathroom circuit is protected by a residual current device (RCD), usually with 30 mA sensitivity, and that the fan has a suitable IP rating for its position. They also check the cable size. Ordinary fans are usually wired with 1.5 mm² cable. A fan with a timer or sensor needs a switched live from the light switch in addition to the permanent live and neutral, so a cable with more cores is often needed. The protective earth conductor must be present in the box, even if the fan itself is double insulated.

A professionally installed fan also matters for the manufacturer's warranty and if you ever need to make an insurance claim.

• Fan far from the shower, for example above the door. The steam condenses on the walls before it reaches the fan.
• No backdraught shutter on a shared shaft. Smells from the neighbours then drift into the flat.
• Overrun wired incorrectly. The fan does not switch off after the light, or it does not run on at all.
• Wires mixed up or earth missing. The fan does not behave as it should and there is a safety risk.
• A model too weak for long ducting. The fan runs, but the damp stays.
• Badly routed cable channels, for example diagonally across the wall. Anyone drilling later can easily hit the cable.
• A fan boxed in by tiling or a suspended ceiling so it cannot be reached for cleaning.

At handover, ask to see the fan working in every mode. Check that:

• The fan is firmly mounted and does not rattle or vibrate
• The joint with the ducting or shaft is sealed
• A sheet of paper held against the grille is clearly drawn towards it
• It switches on as agreed: by switch, with the light or by the sensor
• The overrun is set and the fan switches itself off afterwards
• With a humidity sensor, the sensitivity is set and you know how to change it
• The backdraught shutter moves freely and closes when the fan stops
• The channels are filled and the area is left clean
• The grille can be reached for cleaning
• You have the instructions and know which circuit breaker controls the fan