Part F Extract Fan Requirements
Fan sizing, noise limits, duct derating, and timer requirements for domestic extract ventilation, referencing Approved Document F: Ventilation, Volume 1 - Dwellings (2021 edition, effective 15 June 2022).
Minimum Fan Extract Rates by Room
| Room | Intermittent (l/s) | Continuous Low (l/s) | Continuous Boost (l/s) |
|---|---|---|---|
| Kitchen (adjacent to hob) | 30 | 13 | 30 |
| Kitchen (remote from hob) | 60 | 13 | 60 |
| Utility room | 30 | 8 | 30 |
| Bathroom (with bath/shower) | 15 | 8 | 15 |
| WC (no bath/shower) | 6 | 6 | 6 |
Noise Limits for Extract Fans
| Room Type | Max. Noise Level dB(A) | Applies To |
|---|---|---|
| Bedrooms | 30 dB(A) | Continuous systems (MEV/MVHR) |
| Living rooms | 35 dB(A) | Continuous systems |
| Kitchens | 35 dB(A) | Continuous running mode |
| Bathrooms/WCs | No specific limit | Short-duration intermittent use acceptable |
Duct Length Derating Guide
Fan performance must be assessed at the installed system resistance. The following shows typical derating for a 100 mm diameter duct system.
| Duct Configuration | Approx. Resistance (Pa) | Typical Flow Loss |
|---|---|---|
| 1 m straight + grille | 10-15 Pa | 5-10% |
| 2 m straight + 1 bend + grille | 20-30 Pa | 15-25% |
| 3 m straight + 2 bends + grille | 35-50 Pa | 25-40% |
| 4 m+ straight + 3 bends + grille | 50-70 Pa | 35-50% |
| Each additional 90° bend | ~10 Pa | Equiv. ~1.5 m straight duct |
Timer and Control Requirements
| Requirement | Detail |
|---|---|
| Bathroom overrun timer | Minimum 15 minutes after switching off |
| Boost mode activation | Manual switch, PIR sensor, or humidity sensor |
| Continuous fan isolation | Must not be easily switched off by occupants (no local switch on continuous systems) |
| Commissioning | All fans must be tested/commissioned and flow rates recorded |
Related Calculators
Use the Ventilation Calculator for full sizing, or the Part F Ventilation Rates page for the complete ventilation strategy overview.
Always check the latest edition of Approved Documents on the Planning Portal (planningportal.co.uk) as regulations are updated periodically.
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Last updated: April 2026
All calculations are estimates. Verify with your supplier.