Technical Booklet K Ventilation·Page 28·2.33
Extract fan overrun in internal rooms
Intermittent extract fans in rooms with no openable windows must continue running for at least 15 minutes after activation, unless controlled by a humidistat.
In a room with no openable window (i.e. an internal room) an intermittent extract fan should have an overrun of at least 15 minutes except where it is controlled by a humidistat. In rooms with no natural light, the fans could be controlled by the operation of the main room light switch.
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