Quick answer: Work out your bathroom's volume (length × width × height in metres) and multiply by 7 to get the airflow you need in cubic metres an hour. Choose a fan that meets that figure and at least the Building Regulations minimum of 15 litres a second (54m³/hr). An axial fan suits a bathroom with an outside wall; an inline fan suits longer duct runs and larger rooms. A run timer keeps it clearing the air after you leave.
- Shop all bathroom extractor fans
- Small and medium bathrooms: Ventus axial fan
- Larger bathrooms and longer duct runs: Ventus Pro inline fan kit
At a glance
- Size: our fans fit a standard 100mm (4 inch) duct.
- Airflow: Ventus axial up to 80m³/hr; Ventus Pro inline 165 or 234m³/hr (twin speed).
- Timer: every Ventus has a run timer, set at installation between 2 and 30 minutes.
- Noise: Ventus axial runs at 36dB measured 2m away.
- Zones: Ventus axial is IPX4 and Ventus Pro IP44, both suitable for Zone 2 on a wall or ceiling.
- Fitting: wired in by a qualified electrician.
Do I need an extractor fan in my bathroom?
In most bathrooms, yes. A shower or bath fills the room with warm, moist air. Without ventilation it settles as condensation on cold walls, windows and ceilings, which leads to peeling paint, damp and black mould. An extractor fan removes that moist air at the source. An opening window helps, but it isn't a reliable substitute, especially in winter when it stays shut.
What do Building Regulations say about bathroom fans?
In England, Approved Document F sets the ventilation required for bathrooms. For an extractor fan that runs when the room is in use, the minimum extract rate is 15 litres a second, which is 54 cubic metres an hour. Rules differ slightly in Wales, Scotland and Northern Ireland, so your electrician or installer will confirm what applies to your home.
What size extractor fan do I need?
Start with the room, not the fan. Multiply the length, width and height of your bathroom in metres to get its volume, then multiply by 7. That gives the airflow in cubic metres an hour for about seven air changes an hour. For example:
- Small bathroom (2m × 1.8m × 2.4m = 8.6m³): about 60m³/hr. A Ventus axial (80m³/hr) covers it.
- Medium bathroom (2.5m × 2m × 2.4m = 12m³): about 84m³/hr. A Ventus axial is borderline; the Ventus Pro on low speed (165m³/hr) gives headroom.
- Large bathroom or en-suite with a long duct run: the Ventus Pro on high speed (234m³/hr).
Always choose a fan that meets both your room figure and the 54m³/hr minimum. Long or bendy duct runs reduce the airflow you actually get, so allow some extra.
Axial or inline: which do I need?
Axial fans fit straight into the wall or ceiling and push air a short distance to the outside. They suit most homes where the bathroom has an outside wall or a short duct to the roof. The Ventus axial comes in white or black.
Inline fans sit in the loft or ceiling void, between a grille in the bathroom and a vent outside. They are more powerful, cope with longer duct runs and are quieter in the room because the motor is out of the way. The Ventus Pro comes as a kit with the inline fan, flexible aluminium ducting, a square white external grille and two round internal grilles, one black and one white.
Timer, humidistat or switch: what's the difference?
- On/off switch: the fan runs only while it's switched on, often with the light.
- Run timer: the fan keeps running for a set time after the light goes off, so steam is cleared after you leave. Every Ventus has a run timer, set at installation between 2 and 30 minutes.
- Humidistat: the fan switches itself on when the air gets humid. Useful where people forget to switch fans on, though our current Ventus models use a run timer instead.
How quiet is a bathroom extractor fan?
Fan noise is measured in decibels (dB), usually at a set distance. The Ventus axial runs at 36dB measured 2m away, about the level of a quiet room at night. Inline fans like the Ventus Pro sit away from the bathroom, so you hear less of them in the room.
Which zone can an extractor fan go in?
Bathrooms are split into zones around the bath and shower. Zone 2 runs 0.6m beyond the edge of the bath or shower. The Ventus axial is IPX4 rated and the Ventus Pro is IP44 rated, so both are suitable for Zone 2 on a wall or ceiling. Your electrician will confirm the right position. Our guide to IP ratings and bathroom zones explains the zones in more detail.
Do I need an electrician to fit an extractor fan?
Yes. A bathroom extractor fan is wired into your electrics in a room with water, so it should be fitted by a qualified electrician, who will make sure it meets Building Regulations. Fans with a run timer are usually wired to the light switch with a separate isolator switch, so the timer can work and the fan can be turned off safely for cleaning.
Can I replace my old fan with a new one?
Usually, yes. Most bathroom fans use a standard 100mm (4 inch) duct, the same size as the Ventus range, so a like-for-like swap often uses the existing hole and ducting. Check the hole size and the face plate size before you order: the Ventus axial plate is 158mm × 158mm.
How do I keep my extractor fan working well?
Switch off at the isolator and wipe the grille every few months, as dust and fluff cut airflow. Leave the fan to run for its full timer after every shower or bath, and keep the bathroom door closed while it runs, so it draws moist air out rather than pulling it round the house.
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