Extractor Fan & Ventilation Rate Calculator
Check an extractor fan’s measured rate against UK Approved Document F minimums, convert litres per second to air changes per hour, and size purge ventilation — for Bosch and other-brand fans, condensation, mould and Healthy Homes assessments.
Room Details
30 l/s if adjacent to the hob (or 60 l/s elsewhere) — Approved Document F
Enter an anemometer reading at the installed fan, or a manufacturer-rated duty as a provisional value. Brand and model do not change the target rate.
Indicative intermittent extract minimum under Approved Document F. Verify against the current edition.
Measured 0 l/s is below the 30 l/s indicative minimum. Increase the fan duty or check for blocked ducting.
Healthy Homes (New Zealand): kitchens and bathrooms must have extractor fans that vent to the outside, and living rooms, kitchens and bedrooms must have openable windows — mandatory for all private rentals since 1 July 2025.
Ventilation rate FAQs
What is the minimum extract ventilation rate for a kitchen or bathroom in the UK?
Under Approved Document F of the Building Regulations (England), the indicative intermittent extract minimums are 30 l/s for a kitchen adjacent to the hob (60 l/s elsewhere), 30 l/s for a utility room, 15 l/s for a bathroom, and 6 l/s for a WC. Always check the current edition of Part F for the rates that apply to your project.
How do you convert an extract rate (l/s) into air changes per hour (ACH)?
Multiply the continuous flow rate in litres per second by 3.6 to get cubic metres per hour, then divide by the room volume in cubic metres. So ACH = (flow in l/s × 3.6) ÷ (floor area × ceiling height).
What does New Zealand’s Healthy Homes ventilation standard require?
New Zealand’s Healthy Homes Standards (mandatory for all private rentals since 1 July 2025) require openable windows in living rooms, dining rooms, kitchens and bedrooms, and extractor fans that vent to the outside in kitchens and bathrooms, to control moisture and mould.
Why does ventilation matter for damp and mould?
Inadequate ventilation lets moisture-laden air build up, raising surface relative humidity and condensation risk. Meeting the recommended extract rates removes moisture at source, which is a key control for condensation and mould growth and supports compliance duties such as Awaab’s Law.
Can I check the extraction rate of a Bosch or another-brand fan?
Yes. This calculator is brand-neutral: enter a measured flow rate or the fan’s documented duty, select the room type and compare the result with the indicative Approved Document F minimum. It does not verify a particular fan model, installation, duct route or commissioning result; measure the installed system where the result matters.
Log ventilation readings on-site, automatically.
DampApp Pro™ records extract-fan readings, room-by-room ventilation checks and psychrometric data natively offline, then outputs RICS-aligned reports — useful evidence for Part F, Healthy Homes and Awaab’s Law duties.
