What airflow rating does a bathroom fan need to meet UK Part F regulations?
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According to the UK Government’s Part F ventilation guidelines, a bathroom extractor fan must achieve a minimum airflow of 15 litres per second (l/s). However, the required fan size and power may vary depending on the room size, ducting length, and user preferences.
How far can I duct an axial, centrifugal, or inline bathroom fan?
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Ducting distance varies by fan type: Axial fan: Up to 2 metres with two 90° bends Centrifugal fan: Up to 6 metres with two 90° bends Inline mixed-flow fan: Up to 20 metres with two 90° bends These are best-case figures. Actual performance depends on the exact duct route and whether rigid or flexible ducting is used.
What is the maximum ducting length for a bathroom extractor fan with bends?
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As a rule of thumb: Axial: ~2m Centrifugal: ~6m Inline: ~20m Every bend increases resistance, so long or complex routes may require a stronger fan type to maintain airflow.
Does duct length affect how powerful my bathroom fan needs to be? +
Yes. Longer or more restrictive ducting requires a more powerful fan to maintain the correct airflow. Short, straight ducting → axial fans are often sufficient. Longer or bend-heavy ducting → centrifugal or inline mixed-flow fans perform much better.
How long do bathroom extractor fan timers run on for? +
Timer overrun varies by model, but most bathroom fans with a built-in timer run for between 2 and 30 minutes after being switched off.
Are bathroom fan overrun timers adjustable? +
Yes. Nearly all timer-based bathroom fans have adjustable settings, usually via an internal dial, allowing you to set the overrun duration anywhere from 2 to 30 minutes, depending on the product.
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