Extractor Fan Buyer's Guide
Bathroom, kitchen, and whole-house extractor fans compared. UK Building Regulations sizing requirements explained.
Extractor fans remove moist, stale air from kitchens and bathrooms. UK Building Regulations Part F 2021 requires 15 L/s intermittent or 8 L/s continuous extract in bathrooms, and 30 L/s intermittent or 13 L/s continuous in kitchens. Fans must vent directly outside, not into lofts. Continuous-run fans with humidity sensors are more effective than basic on/off models. Installation costs £100-£300 depending on ductwork complexity. Running costs are £10-£20/year for continuous models.
Types of Extractor Fan
Intermittent Extract (On/Off)
Runs only when switched on, usually linked to the bathroom light switch. Must provide 15 L/s in bathrooms, 30 L/s in kitchens. Should run for 15-20 minutes after use to clear residual moisture. Many models have an adjustable overrun timer.1
Pros: simple, low cost (£30-£80). Cons: users forget to leave them running, so moisture removal is incomplete.
Continuous Extract (Low-Speed with Boost)
Runs 24/7 at low speed (8 L/s in bathrooms, 13 L/s in kitchens), with boost mode when the light is on or humidity rises. More effective because moisture is removed steadily, not in bursts.
Pros: better moisture control, lower peak noise (quiet trickle mode most of the time), meets Building Regs continuous ventilation requirement. Cons: higher upfront cost (£80-£150), runs continuously (but energy use is low, typically 3-5W in trickle mode).2
Humidity-Sensing Fans
Automatically boost when indoor humidity exceeds a set threshold (usually 60-70% RH). No manual switching needed. Ideal for households where people forget to turn fans on.
Inline Duct Fans
Installed in the ductwork (in the loft or void), not in the ceiling or wall grille. Quieter in the room because the motor is remote. Useful when ducting is long or complex. Cost: £150-£300 plus installation.
How to Size an Extractor Fan
Building Regulations Part F 2021 sets minimum extract rates:1
- Bathroom (with bath or shower): 15 L/s intermittent OR 8 L/s continuous
- Kitchen (with hob): 30 L/s intermittent (adjacent to hob) OR 13 L/s continuous OR 60 L/s intermittent (elsewhere in room)
- Utility room: 30 L/s intermittent OR 8 L/s continuous
- WC (separate from bathroom): 6 L/s intermittent OR 6 L/s continuous
For large bathrooms (over 10 m²), increase extract rate proportionally. A 4m × 3m bathroom (12 m²) needs approximately 18-20 L/s intermittent.
Installation Requirements
Extractor fans must vent directly outside through an external wall or roof. Venting into lofts, voids, or other rooms is not compliant and causes condensation damage.1
Duct runs should be as short and straight as possible. Every 90° bend reduces airflow by approximately 10-15%. Use rigid ducting (not flexible corrugated) for better airflow and easier cleaning.
Fans in bathrooms with showers must be IPX4-rated (splash-proof). Fans within 60cm of a shower head or bath tap must be low-voltage (12V) or installed by a qualified electrician to meet Part P wiring regulations.
Costs
- Fan Unit Cost
- £30-£150 (continuous models higher)
- Installation Cost
- £100-£300 (inc. electrician + ductwork)
- Annual Running Cost
- £10-£20 (continuous at 3-5W)
- Typical Noise Level
- 25-35 dB (trickle), 40-50 dB (boost)
Sources
- HM Government, Approved Document F: Ventilation (2021 edition), Table 1.1a, 2021. gov.uk (accessed 20 May 2026)
- Energy Saving Trust, Domestic Ventilation: Extract Fans and Whole-House Systems, 2025. energysavingtrust.org.uk (accessed 20 May 2026)
- BEAMA (British Electrotechnical and Allied Manufacturers Association), Domestic Ventilation Compliance Guide, 2022. beama.org.uk (accessed 20 May 2026)
Last reviewed: 20 May 2026 | Word count: 892 | Reading time: 5 minutes