Why is cold air blowing in through my extractor fan?

This is a common complaint in winter and one that people often solve by taping over the fan, which stops the ventilation the bathroom needs and creates a condensation problem in exchange for a draught. The shutter is a simple mechanical part and it is nearly always the culprit.

Safety

Step by step

1. Find out where the shutter is.There may be one at the fan itself, one at the external terminal, or both. Working out which is not closing tells you where to look.
2. Clean the shutter at the fan.Dust and lint build up on the flaps and the hinge until they no longer swing shut. This is the commonest cause and cleaning is often the whole repair. Isolate the power first.
3. Check the external shutter as well.Painted, seized, or held open by debris. GuideHQ has a guide on external vent problems, and the same inspection covers both faults.
4. Consider wind pressure on an exposed elevation.A light gravity flap on a wall that takes the prevailing wind can be pushed open. A terminal designed for exposure, or a shutter that closes positively rather than by gravity, deals with it.
5. Check the fan is the right way round and level.A gravity shutter relies on being fitted the right way up. One mounted rotated or in the wrong orientation may not close under its own weight.
6. Do not block or tape over the fan.It removes the ventilation that stops the room getting damp. Trading a draught for condensation and mould is a poor deal, and the damage takes longer to notice.
7. Consider a replacement fan with a better shutter.Some fans have poor shutters, and some have none at all. Where cleaning does not fix it, the shutter design may simply be inadequate. Installation is electrical work.
8. Check the duct is insulated while you are in there.Cold air in the duct also causes condensation inside it, which produces the drip that GuideHQ covers separately. The two faults often appear together.

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