Extractor Fan Installation Guide
A bathroom extractor is a small job with real detail: the right fan for the zone, correct IP rating, a means of isolation, and compliance with the ventilation rules.
Extractor fans deal with the moisture and smells that cause condensation, mould and damage. In a bathroom the job carries extra requirements because it's a special location — the fan's position relative to the zones dictates its IP rating and how it must be wired, and there are ventilation rules to meet as well as electrical ones.
This guide covers choosing the fan and its features, the bathroom zones and IP ratings, wiring and isolation, and certification. It assumes installation to BS 7671, Amendment 2, alongside the Building Regulations ventilation requirements, with safe isolation before work.
Key takeaways
- Choose the fan for the room and duty — with timer/overrun or humidity control as needed.
- In a bathroom, the fan's zone dictates its required IP rating and wiring.
- Provide a means of isolation — commonly a fan isolator (a triple-pole switch for timer fans).
- Meet the Building Regulations ventilation extract rate for the room.
- Test and certify the work with a Minor Works Certificate.
Choosing the fan
Match the fan to the room and its extract duty. Common features are a timer/overrun (runs on after the light is switched off), a humidity sensor (runs when moisture rises), and a trickle setting for continuous low-level ventilation. Bathrooms usually take an axial fan on a short duct; longer duct runs or kitchens may need a more powerful centrifugal or inline fan to overcome the resistance.
Size it to achieve the required extract rate for the room — an underpowered fan on a long duct simply won't clear the moisture, whatever its badge says.
Bathroom zones and IP ratings
A bathroom is a special location under BS 7671 Section 701, divided into zones by proximity to the bath or shower. The fan's position determines the minimum IP rating: a fan within a wet zone (for example over a shower) needs a higher IP rating (such as IP65) and must be low voltage or otherwise suitable for that zone, whereas one mounted high on a wall away from the zones has less onerous requirements.
Establish where the fan sits relative to the zones before you choose it — retrofitting a higher-rated fan because you picked the wrong one is avoidable.
Zone dictates the fan
Decide the fan's position against the Section 701 zones first, then choose an IP rating and supply arrangement that suits that zone. The zone drives the specification, not the other way round.
Doing this on a job? Max Zs calculator — part of TradePlanr. Free to start, no card needed.
Wiring and isolation
A timer or overrun fan needs a permanent live, a switched live (from the lighting) and a neutral, plus CPC — so it's typically wired via a fan isolator that switches all poles, giving both control and a local means of isolation for maintenance. A basic fan switched with the light needs fewer cores but still needs a means of isolation.
Fit the isolator outside the bathroom zones (commonly a ceiling-mounted triple-pole isolator) so the fan can be safely isolated for cleaning or replacement without pulling the lighting circuit.
Certify the work
Where the job alters or extends a circuit, issue a Minor Works Certificate from TradePlanr with the test results, so the work in the special location is properly recorded.
Ventilation rules and certification
Beyond the electrics, the fan must meet the Building Regulations ventilation requirements — an intermittent extract fan in a bathroom must achieve the required extract rate, and there are rules about background and purge ventilation for the room. Ducting should be as short and direct as practical and terminate outside, not into a loft void.
Test the electrical work (continuity, insulation resistance, polarity, Zs, RCD) and certify it. In a bathroom, RCD protection applies and the special-location rules must be satisfied.
From guidance to action
Frequently asked questions
What IP rating does a bathroom extractor fan need?
It depends on the fan's position relative to the Section 701 zones. A fan within a wet zone needs a higher rating (such as IP65) and a suitable supply, while one mounted high and away from the zones has less onerous requirements.
How is a timer extractor fan wired?
A timer/overrun fan needs a permanent live, a switched live from the lighting, a neutral and CPC, usually via a triple-pole fan isolator sited outside the bathroom zones so it can be isolated for maintenance.
Does an extractor fan installation need certifying?
Where it alters or extends a circuit, yes — test it and record the results on a Minor Works Certificate. In a bathroom the special-location rules and RCD protection apply, and Building Regulations set the ventilation extract rate.
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