Property management
Ventilation Fan Calculator
Fans are sized by air changes: how many times an hour the room's whole volume should pass through the duct.
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How it works
Airflow = room volume x air changes per hour. Typical targets: kitchens 15, bathrooms 8, living rooms 6. Also check code minimums - UK Part F wants 60 L/s intermittent in kitchens (13 with a hood over the hob) and 15 L/s in bathrooms.
Frequently asked questions
What size extractor fan for a bathroom?
A 2.5 x 2 m bathroom with a 2.4 m ceiling at 8 air changes needs ~96 m3/h (27 L/s) - comfortably above the UK Part F 15 L/s minimum. Duct length eats performance, so size up on long runs.
Why does my bathroom still get mould with a fan?
Run-time and airflow. A fan needs 15-20 minutes of overrun after showers, a clear duct, and an actual gap under the door for replacement air - pair this with the condensation risk calculator.