Last Updated on October 25, 2026 by Umar Farooq
Should extractor fans be on all the time? Only if they are designed to be: a continuous trickle fan is meant to run constantly, while an ordinary bathroom or kitchen fan is meant to run during use and for a while afterwards. The label, not your preference, decides.
This is one of those questions where both camps are right and the argument goes on because each is describing a different fan. One person has a quiet, low-power fan that has been humming since the house was built. Another has a noisy pullcord unit that would be happier left alone for twenty-two hours a day.
Should extractor fans be on all the time? It depends which kind you have
| Fan type | Meant to run all the time? | How it usually behaves |
|---|---|---|
| Continuous (trickle) fan | Yes | Low speed constantly, with a boost for showers or cooking |
| Timer fan | No | Runs on when the light or switch is used, then stops after a set time |
| Humidity sensor fan | No | Runs when humidity rises, stops when it falls |
| Pullcord or switched fan | No | Runs until you switch it off |
England’s ventilation guidance accepts either approach. Approved Document F says extract ventilation can be intermittent or continuous, and gives separate minimum rates for each: for a bathroom, 15 litres a second for an intermittent fan, or an 8 litres a second high rate for a continuous system.
How to tell which you have: read the model name and manual. A continuous fan will say so, for example Vent-Axia’s Centra Lo-Carbon range is sold as a “continuous extract fan” with a selectable trickle speed of 6 or 9 litres a second and a boost to 15 litres a second. If you have no manual, the make and model number on the fan, found by taking off the front, usually find one online.
Why a continuous fan runs all day
A continuous fan is not just an extractor; it is a small part of a whole-house ventilation plan. Approved Document F sets a whole-dwelling rate in litres a second, for example 31 l/s for a three-bedroom home, and the continuous extract rates in the wet rooms add up towards it. Running slowly all the time moves a steady trickle of air, so there is no sudden wet spike to deal with.
It also uses little. The same Vent-Axia instruction sheet lists a maximum power input of 2.4 W at 54 m³/h. Are extractor fans expensive to run does the pence-a-year sums.
West Lothian Council’s damp and mould guide makes the practical point: some fans are designed to be constantly running and should not be disconnected. If yours is one, do not switch it off at the fused spur to save a penny or end a hum; the damp will cost you more.
What if you leave an ordinary fan on all the time?
I found no manufacturer statement that running a standard fan continuously is dangerous, and I would not claim one. The honest reasons not to do it are practical:
- Wasted heat. A fan that runs all day in winter expels warmed air for no reason once the steam has gone.
- Cost. On the sums in the running-cost article, a typical 20 W fan running all the time is about £43.80 a year at 25p per kWh, against about £1.83 for an hour a day. Those are my figures, based on one datasheet’s rating.
- Noise and wear. A fan not built for the duty is simply being asked to do more hours; the bearings do not know it is a hobby.
Check the manual before making an ordinary fan continuous. If you want the benefit of continuous ventilation, buy a fan made for it.
When a fan seems to run all the time by accident
If a timer or humidity sensor fan never seems to stop, there are two innocent explanations before you suspect a fault:
- The sensor is doing its job. A humidity sensor fan stays on while the humidity is above its set point, which can be a long time in a damp house. Humidity sensor extractor fans explains the settings.
- The timer is set long. Many timers have an adjustable run-on; the Manrose XF100T’s, for example, is labelled in minutes with a wheel on the unit.
If neither fits, switch it off at the isolator and ask an electrician to check the wiring. Do not poke around in a mains fan yourself.
Leave a continuous fan alone and put an ordinary one on a timer
So, should extractor fans be on all the time? A continuous one, yes, and leave it alone. An ordinary one, no: it should run while you use the room and for a while after, which how long to run a bathroom extractor fan pins down. If a fan is on all day and was not built to be, change the control, not the habit.
Not sure whether you need one at all? Do I need a bathroom extractor fan is the place to start.
FAQ
Is it OK to leave a bathroom extractor fan on all day?
If it is a continuous-rated fan, yes, that is what it is for. For an ordinary fan, I found no manufacturer warning against it, but it wastes heated air and costs more, so a timer is better.
Do continuous extractor fans use a lot of electricity?
No. One manufacturer’s continuous fan lists a maximum power input of 2.4 W, which comes to around £5 a year on the 25p per kWh sums used in this site’s running-cost guide.
Should I turn off a trickle fan?
No. West Lothian Council advises that fans designed to be constantly running should not be disconnected.
How do I know if my extractor fan is continuous?
Check the model name and manual: continuous fans are sold as such and usually have a trickle speed and a boost. A fan that only runs when you use the switch is intermittent.
Why does my extractor fan keep running?
It may be a humidity sensor fan waiting for the humidity to drop, a timer set to a long run-on, or a continuous fan working as designed. If none of those fits, have the wiring checked.
