Bathroom Extractor Fans: Sizing, Timers and Run-On
Choose a bathroom extractor fan by its extract rate (how much air it moves, in litres per second or cubic metres per hour) matched to the room, so it clears the moist air adequately a bigger or busier bathroom needs a higher extract rate, and there's a minimum ventilation requirement to meet. It must have the right IP rating for where it's fitted, because bathrooms have zones based on proximity to water (a fan near or over a shower needs a suitable IP rating). Controls make it effective: a timer or run-on keeps the fan going for a period after the light is switched off (or after use), clearing the moisture, and a humidistat can switch it on automatically when humidity rises. Install to IS 10101 and the ventilation requirements.
A bathroom extractor fan has one job get the moist air out before it turns into condensation and mould and a surprising number are the wrong size, the wrong rating, or set up so they never run long enough to work. Getting the sizing, the IP rating and the controls right is what makes a fan actually clear a bathroom, as supplied by Waveform Electrical Wholesale. Here's how.
Sizing by extract rate
A fan is only useful if it moves enough air for the room. Extract rate quoted in litres per second (l/s) or cubic metres per hour (m³/h) is the measure, and it needs to suit the bathroom's size and use: a small WC needs less than a busy family bathroom or a room with a power shower. There's a minimum ventilation provision to meet, and undersizing is a common cause of persistent condensation because the fan simply can't clear the moisture generated. Match the extract rate to the room, not the cheapest fan.
IP ratings and bathroom zones
Bathrooms are divided into zones based on how close to water an item is (over the bath or shower, immediately around it, and beyond), and electrical equipment in each zone needs a suitable IP (ingress protection) rating. A fan fitted over or near a shower needs an appropriate IP-rated fan for that zone. Choosing a fan with the right IP rating for its position isn't optional it's a safety and compliance requirement, and part of installing to IS 10101.
Timers, run-on and humidistats
- A timer / run-on keeps the fan running for a set period after the light (or fan) is switched off, so it clears the moisture that lingers after a shower.
- Without run-on, a fan that stops the moment you leave often hasn't cleared the humidity.
- A humidistat switches the fan on automatically when humidity rises and off when it falls useful where the fan isn't tied to the light.
- These controls are what make a fan actually deal with moisture rather than just run while you're in the room.
Meeting the requirements
Bathroom ventilation has to meet the ventilation requirements for the room, and the fan has to be wired safely for its zone. Getting the extract rate, IP rating and controls right together is what delivers a bathroom that stays dry and mould-free. WEW stocks bathroom extractor fans, timers, humidistats and inline options across Meath see inline, window or wall extractor for the fan type and condensation and mould for tackling a moisture problem. Install by a Safe Electric registered electrician to IS 10101.
Frequently asked questions
What size bathroom extractor fan do I need?
One with an extract rate (l/s or m³/h) matched to the room's size and use a bigger or busier bathroom needs a higher rate and meeting the minimum ventilation requirement. Undersizing is a common cause of persistent condensation, because the fan can't clear the moisture generated. Match the extract rate to the room.
What IP rating does a bathroom fan need?
It depends on where it's fitted. Bathrooms have zones based on proximity to water, and a fan over or near a shower needs a suitable IP rating for that zone. Choosing the right IP-rated fan for its position is a safety and compliance requirement, part of installing to IS 10101.
Why does a bathroom fan need a run-on timer?
Because moisture lingers after a shower, and a fan that stops the instant you leave often hasn't cleared it. A run-on timer keeps the fan going for a set period after the light is switched off, clearing the humidity. A humidistat can also switch it on automatically when humidity rises.
Source it at WEW
WEW (Waveform Electrical Wholesale) is your electrical wholesaler and lighting expert in Meath, supplying fans, ventilation, EV charging and everything electrical to trade and homeowners. Call in to the counter or the showroom for stock, advice and everything referenced in this guide.