Work out the extractor fan airflow your bathroom needs in m³/h and CFM, allowing for duct length and bends.
How this works
Airflow = room volume x air changes per hour. Bathrooms need 8 air changes, or 10 to 15 with a busy shower. We add about 3% per metre of duct and 8% per bend for resistance. 1 m³/h is 0.589 CFM, and the code minimum is 54 m³/h (15 L/s or 50 CFM).
Questions people ask
How do I use the Bathroom Exhaust Fan Size tool?
Fill in the fields, starting with “Room length”, “Room width” and “Ceiling height”, and change any other options that match your home. The answer, a drawing and practical tips update as you type, and the Copy link button saves your numbers in a link you can share.
Is the Bathroom Exhaust Fan Size tool free?
Yes. The Bathroom Exhaust Fan Size tool is free, with no sign-up, and works on phones, tablets and computers. The results are estimates to help you plan, so check with a qualified professional before structural, electrical, gas or plumbing work.