appliances
Extractor fans and ventilation
A bathroom fan fitted costs £120 to £300 where a fan already exists and there is a route out. The figure that moves it is the duct, not the fan: getting air from an internal bathroom to an outside wall is most of the labour and all of the difficulty.
What this covers
What it costs. A replacement fan where one already exists is £120 to £300. Full cost breakdown.
What the job covers
- Fitting a bathroom fan with an overrun timer
- Ducting through a wall, soffit or roof tile
- Humidity sensing fans in rooms with no window
- In line fans for a shower cubicle
- Replacing a noisy or seized unit
What is involved
Building regulations set a minimum extract rate for a room without an opening window, and for a bathroom that is 15 litres a second. A fan achieves that figure on a test bench with no duct attached. Put four metres of flexible duct with two bends on it and the real rate can halve, which is why a bathroom with a new fan can still steam up. Rigid duct on the shortest run beats a more powerful fan on a bad one every time, and it is the single thing worth spending on.
Three switching arrangements cover most installations. A fan wired to the light with an overrun timer runs on while the light is on and for a set period after, which is the common domestic answer and needs a three core supply to the fan. A humidity sensing fan runs when the air is wet regardless of the light, which suits a bathroom used with the light off in summer. A pull cord model switches independently. The timer version is the one that needs the extra conductor, and in a house where the lighting loops at the rose there may not be one.
Where the duct goes decides the job. An outside wall behind the fan is a core drill and an afternoon. A roof tile vent means a roofer or a competent installer on the tiles. A soffit run through the loft wants insulated duct, because warm wet air in a cold loft condenses inside the pipe and runs back down into the fan, which is the commonest cause of a fan that drips.
Choosing someone for the job
Ask what the duct run will be and what it is made of, and push for rigid over flexible. Ask where the air comes out. Ask whether the fan is timed, humidity sensing or pull cord, and whether the existing wiring has the conductor a timer needs. In a loft run, ask whether the duct is insulated.
Common questions
My new fan does not seem to clear the steam.
Nearly always the duct rather than the fan. Long flexible runs with bends can halve the rate a fan achieves on the bench. Shortening the run, straightening it, or changing flexible for rigid usually fixes it without touching the fan.
Does a bathroom fan have to be on a timer?
No. What is required is the extract rate for the room. A timer is a convenience that keeps it running after the light goes off, and a humidity sensor does the same job without needing the light at all.