Last Updated on October 25, 2026 by Umar Farooq
Are extractor fans expensive to run? No: a typical bathroom fan costs well under a penny an hour, and one council leaflet puts extractor fans at typically less than 1p an hour. Even a low-power fan left running all year costs about a fiver, on the electricity rate I have used below.
The more interesting question is what a fan costs you indirectly, which is heated air thrown out of the window. I will get to that, because it is the part everybody skips.
Are extractor fans expensive to run? The sum in watts
Two datasheets give the power range. Vent-Axia’s installation instructions for its Centra Lo-Carbon continuous fans list a maximum power input of 2.4 W at a maximum flow of 54 m³/h (15 litres a second). Manrose’s XF100T timer fan is labelled 20 W. I found those two and no more, so treat them as examples of the low and ordinary end, not a survey.
Cost is watts × hours ÷ 1,000 × the price of a unit. I have used 25p per kWh purely for the sums; swap in the rate on your own bill. The arithmetic is mine, not a published figure.
| Fan and pattern | Energy a year | Cost a year at 25p/kWh |
|---|---|---|
| 20 W, 30 minutes a day | about 3.7 kWh | about 91p |
| 20 W, 1 hour a day | about 7.3 kWh | about £1.83 |
| 2.4 W, running all the time | about 21 kWh | about £5.26 |
| 20 W, running all the time | about 175 kWh | about £43.80 |
The last row is the useful one. A fan left running 24 hours a day only starts to cost real money if it is an ordinary 20 W unit that was never designed to be on constantly. A fan designed for continuous running draws a fraction of that.
West Lothian Council’s damp and mould guide says extractor fans are very cheap to run, typically less than 1p an hour. At 25p a unit, 20 W is 0.5p an hour, which squares with that.
Where the real cost hides: warm air going outside
A fan has to replace the air it removes, and in winter that air arrives cold. The fan’s own electricity is trivial; the heat you paid for and then expelled is the larger item. I cannot give you a figure, because it depends on your heating, your house and how long the fan runs, and I will not invent one.
What I can say is that it scales with run time. A short run-on after a shower removes the steam where it is made. A fan left on for hours in a winter bathroom is removing heated air long after the steam has gone. How long is enough is in how long to run a bathroom extractor fan.
Four ways to keep the bill small
- Use a timer, not memory. A timer fan stops itself. A pullcord fan runs until someone remembers.
- Consider a humidity sensor. It runs when the room is humid and stops when it is not; the limits are covered in humidity sensor extractor fans.
- Keep it clean and clear. A blocked grille or duct cuts airflow, so the fan runs longer for the same effect. The Building America bathroom guide says to vacuum the cover and blades and check that the duct termination is not clogged. How to clean an extractor fan has the safe order of steps.
- Do not run a non-continuous fan all day. If a fan is meant for continuous running it will say so; should extractor fans be on all the time explains how to tell.
Compared with the problems a fan prevents
Fans are cheap next to the alternatives, and the relevant comparison is with a dehumidifier. Their running cost is worked through in dehumidifier running cost. A fan removes steam at source; a dehumidifier clears what is left. They are not rivals, and the fan is almost always the cheaper first move.
Pennies a year, plus a short run-on: the fan is not the expensive part of damp
An extractor fan is among the cheapest things in the house to run. Worry about the heat it removes, not the electricity it uses, keep the run-on short, and clean it once in a while.
FAQ
How much does it cost to run an extractor fan per hour?
For a 20 W fan at 25p per kWh, about half a penny an hour. West Lothian Council’s guide says typically less than 1p an hour. Your own unit rate and the fan’s rated watts give the exact figure.
How much does it cost to run a bathroom extractor fan all year?
On the same 25p sums, about £1.83 a year for an hour a day with a 20 W fan, and about £5.26 for a 2.4 W continuous model running all the time.
Do cooker hoods cost more to run than bathroom fans?
They can, because they are generally larger and often include lights. I have no datasheet figure for a typical one, so check the power rating on the label.
Is it cheaper to leave an extractor fan on or turn it off?
Turning it off is cheaper in electricity, but leaving a continuous low-speed fan on costs only a few pounds a year. A fan not designed for continuous use should stay on a timer.
Do humidity sensor fans save money?
They can, because they run only when needed. They do not run if the humidity rises slowly or stays below the trigger, so they are not a cure-all.
