On this page
- Replacing a fan and fitting a new one are different jobs
- What changes the price of a replacement
- What decides the cost of a new fan
- How powerful the fan must be
- Bathroom zones decide which fan can go where
- Timer, humidistat and isolator
- When the work has to be notified
- Landlords: a dead fan becomes a damp problem
The short version
- Replacing an extractor fan in London costs from £120, typically £120–£180 including VAT.
- A fan where there was none is priced after a visit, because the wall, duct and power decide it.
- A bathroom fan must extract at least 15 litres a second, and a kitchen fan 30 or 60.
- Replacing a fan is never notifiable, but a new circuit or work around the bath or shower is.
Replacing an extractor fan in London costs from £120, typically £120–£180 including VAT, where the new fan uses the existing hole, duct and cable. Fitting a fan where there was none is a different job. The wall or ceiling, the duct route and the power supply decide it, so it is priced after a visit.
| Job | Guide price (VAT included) |
|---|---|
| Replacing an extractor fan | from £120 (typically £120–£180) |
| Fan stopped working: finding the fault | from £100 |
| New fan where there was none | priced after a visit |
These are guide prices, not fixed quotes. A replacement price covers removing the old fan, fitting and wiring the new one, and testing it.
Replacing a fan and fitting a new one are different jobs
Most price confusion comes from treating these as one job. A like-for-like replacement reuses almost everything. A new installation builds the ventilation route from nothing.
| Replacement | New installation | |
|---|---|---|
| Hole | Existing | New hole or core drilled |
| Ducting | Existing, checked | New run to an outside wall or roof |
| Power | Existing supply | From a nearby circuit, or a new one |
| Building control | Never notifiable | Notifiable in some cases, see below |
| Price | from £120 | After a visit |
What changes the price of a replacement
A replacement usually lands inside the guide range. It moves towards the top when:
- The new fan is a different size or fixing, so the opening needs adapting
- The fan sits in a high ceiling or is only reachable from a loft
- You are upgrading to a timer or humidistat model that needs an extra wire
- There is no local isolator yet, and one has to be added
- The duct turns out to be disconnected or crushed in the ceiling void
If the old fan simply stopped, the fan may not be the problem. A tripped circuit or a failed timer can look the same, which is why finding the fault starts from £100.
What decides the cost of a new fan
A new fan is priced after a visit because these vary so much between London homes:
- The wall: solid brick takes a core drill, a stud wall does not
- Above the ceiling: a loft gives easy access, a flat above does not
- The duct run: its length and route to the outside
- Internal bathrooms: many London flats have no outside wall, so the duct runs further
- Power: taking a supply from the lighting circuit, or running a new circuit
To arrange a visit, see our electrician service in London or call 07727 619854.
How powerful the fan must be
The ventilation rules, Approved Document F, set minimum extract rates for fans that run when a room is in use:
| Room | Minimum extract rate |
|---|---|
| Bathroom | 15 litres a second |
| Kitchen with a cooker hood venting outside | 30 litres a second |
| Kitchen with no hood, or one that does not vent outside | 60 litres a second |
| Utility room | 30 litres a second |
| Separate WC | 6 litres a second |
Where the fan goes
An extract fan should sit as high as practical, within 400 mm of the ceiling, where warm, damp air collects. A cooker hood that only recirculates air does not count as kitchen ventilation on its own.
Air has to get in as well
A fan cannot pull air out of a sealed room. Internal doors need a gap underneath, the equivalent of a 10 mm undercut, so replacement air can reach the fan.
Bathroom zones decide which fan can go where
The wiring rules divide a bathroom into zones around the bath or shower. Any fan in zone 1 or zone 2 must be rated at least IPX4 against splashing water, and suitable for that position.
Every circuit in a bathroom also needs 30 mA RCD protection. Our guide to a fuse box that keeps tripping explains what an RCD does.
Timer, humidistat and isolator
The run-on timer
In a room with no openable window, the fan must keep running for at least 15 minutes after the room is left. That is why a fan wired to the light carries on after the light goes off.
The humidistat
A humidistat starts the fan when the air turns damp. Any automatic control like this should have a manual override, so you can still switch the fan on.
The isolator
A fan with a run-on timer needs a three-pole isolator, which cuts every wire feeding it, so it can be serviced safely. It goes outside the bathroom zones, often just outside the door.
When the work has to be notified
Replacing a fan on its existing cabling is not notifiable to building control. A new fan becomes notifiable if it needs a new circuit, or if it adds to or alters a circuit within the space around the bath or shower: up to 2.25 m high and 0.6 m out from its edge.
A registered electrician handles the notification and gives you a certificate for the work.
Landlords: a dead fan becomes a damp problem
Government guidance on damp and mould tells landlords to check that bathroom and kitchen fans work and vent outside. Serious damp and mould can be a hazard councils must act on. Awaab's Law currently applies to social housing only, but a working fan remains one of the simplest ways to keep a rented bathroom dry.
Frequently asked questions
Yes, if the fan is suitable for that position. Above a bath or shower is zone 1, where a fan must be rated at least IPX4 and approved by its maker for that zone. Adding to or altering a circuit in that space is notifiable, so use a registered electrician.
That is the run-on timer doing its job. In a room with no openable window, the fan should keep running for at least 15 minutes after the room is left, to clear the remaining moisture. A fan that never stops points to a faulty timer or humidistat.
The usual causes are dust clogging the intake, a duct that has come loose or been crushed, a fan too weak for the room, or no gap under the door to let air in. Cleaning to the maker's instructions fixes the first; the others need the fan and duct checked.
Safety guidance is to use a registered electrician. Bathroom circuits need RCD protection, the fan must suit its zone, and the isolator has to be wired correctly. A registered electrician tests the work and certifies it.