How many CFM does a bathroom exhaust fan need?
A bathroom local exhaust fan must move at least 50 cfm if intermittent, or 20 cfm if run continuously (IRC Table M1507.4).
When a bathroom or toilet room is served by a mechanical exhaust fan, the IRC sets the minimum airflow at 50 cfm for an intermittent (on-demand) fan, or 20 cfm for a fan operated continuously.
The exhaust air has to be ducted to the outdoors. It cannot dump into an attic, soffit, crawlspace, or other concealed building space.
These figures are minimums for the local exhaust point itself and are separate from any whole-house ventilation rate the dwelling must also meet.
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Related answers
- How many CFM does a kitchen exhaust fan need? — IRC §M1507.3
- Does a bathroom need a window, or is an exhaust fan enough? — IRC §R303.3
- Where can a clothes dryer vent terminate and does it need a damper? — IRC §M1502.3
- What is the maximum length of a clothes dryer exhaust duct? — IRC §M1502.4.4
- Can HVAC return air be pulled from a bathroom, kitchen, or garage? — IRC §M1602.2
- How much window area do I need for natural light and ventilation in a room? — IRC §R303.1
- How far does a toilet have to be from a side wall or vanity? — IRC §P2705.1
- What is the minimum shower size allowed by code? — IRC §P2708.1
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Adopted edition and local amendments vary by city and county. Ask Donnie checks your jurisdiction and cites the exact adopted section.
Ask Donnie →General information based on the International Residential Code (a model code). This is AI assistance to verify — not legal advice. Confirm the adopted edition and any local amendments with your local building department (AHJ) and a licensed professional before you build.