Do Extractor Fans Stop Mould?

Extractor fans are simple, cheap to run and, when they work, extremely effective. The trouble is how many of them don’t work. On surveys I regularly find fans that are blocked, broken, ducted into the loft, too small for the room, or connected so they stop the moment the light switch goes off.

Why moisture should be removed at source

The best place to remove moisture is where it’s made, before it spreads. That’s the bathroom and kitchen. A good fan pulls steam out as it’s created, so it never reaches the cold bedroom walls.

How to tell if yours is doing its job

• The toilet roll test. Hold a sheet up to the grille while the fan runs. A working fan should pull it against the grille.
• Check where it goes. The duct should go to outside, through a wall, window or roof terminal, not just into the loft or a ceiling void.
• Listen and look. A fan that rattles, a grille clogged with dust, or a backdraught shutter stuck shut all reduce the airflow.
• Check how long it runs. A bathroom fan that stops when you switch the light off is leaving most of the steam behind.

Types of fan

• Intermittent fans run when switched on. Better ones have an overrun timer or a humidistat.
• Continuous-running fans, sometimes called dMEV, tick over quietly all the time and boost when humidity rises. They suit homes with ongoing condensation problems, and nobody needs to remember to turn them on.
• Cooker hoods only extract moisture if they’re ducted outside. Recirculating hoods don’t.

The ducting matters as much as the fan. Long, kinked or squashed flexible duct can throttle a decent fan to almost nothing. Short, straight, smooth runs work best.

Fans are also part of a system. They need replacement air, which is where trickle vents and gaps under doors come in. A fan in a sealed room with the door shut and no air supply can’t do much.

One honest point: noise is the number one reason people switch fans off. If yours is so loud nobody will use it, replacing it with a quieter model is money well spent.