Why does my extractor fan not clear the steam?
Blocked, undersized or venting into the loft — three causes, and the paper test that identifies the first in seconds.
- Difficulty
- beginner
- Time
- 40 min
- Read
- 2 min
- Safety
- warning
Short answer
Hold a sheet of paper against the running fan. If it does not hold it in place, the fan is not moving air — usually because the grille is clogged or the duct is blocked, crushed or venting nowhere.
Bathroom fans fail quietly. They still make a noise, so people assume they work, while the actual airflow has dropped to almost nothing and the mould gets blamed on ventilation habits.
Safety
Step by step
- Do the paper test.Hold a sheet of paper flat against the running fan. A working fan holds it there. If it falls, the fan is moving very little air, whatever noise it makes.
- Clean the cover and the impeller.Power off at the consumer unit first. The cover clips off and is usually thick with dust. So is the fan blade behind it — that is often the whole problem.
- Check where it actually vents.It should vent outside, through a wall or the roof. A surprising number vent into the loft, which is both useless and causes condensation in the roof space. Look in the loft and follow the duct.
- Check the duct is not crushed or disconnected.Flexible ducting kinks, sags and comes off. A long run with several bends dramatically reduces airflow even when everything is connected.
- Check the external grille.Painted over, blocked with debris, or fitted with a flap that has stuck shut. Look at it from outside while the fan runs.
- Check the fan is powerful enough for the room.Fans are rated in cubic metres per hour. A builder's-basic fan in a large bathroom with a shower is undersized from the start.
- Make sure air can get in.A fan cannot extract from a sealed room. A gap under the door, or a vent, is needed for replacement air. Draught-proofing a bathroom door stops the fan working.
- Fit a humidity-sensing fan with an overrun.It runs when the humidity rises and continues after you leave. The single best upgrade for a bathroom that keeps growing mould.
Tips
- The twenty minutes after a shower is when the fan does most of its work. A fan wired to the light switch stops exactly when it is most needed.
- Keep the door closed while the fan runs, with just a gap at the bottom. An open door lets moist air into the rest of the house instead.
- If the fan vents into the loft, that is causing damage up there as well. It is worth fixing properly rather than living with.
Questions people ask
How do I know if my extractor fan is working?
Hold a sheet of paper against it while it runs. A working fan holds the paper in place. Noise is not evidence of airflow.
Where should a bathroom fan vent to?
Outside, through a wall or roof. Venting into a loft is both ineffective and causes condensation and rot in the roof space.