Purge Ventilation Fans

Purge Ventilation Fans

The Approved Document F and the Scottish Technical Handbook set out guidelines for purge ventilation, over and above the nominal and boost ventilation requirements.

It is a form of emergency extract ventilation, e.g. when there is a need for purging heat from solar gains or smells from painting. Purge ventilation is needed for all habitable rooms (living spaces, bedrooms, studies, etc.).

In most cases purge ventilation is achieved by openable windows and doors to the outside:

• The size of sash windows, doors and hinged and pivot windows with opening angle of 30 degrees or more is at least 1/20th of the floor area of the room.
• The size of hinged and pivot windows with opening angle of 15 to 30 degrees is at least 1/10th of the floor area of the room.

If there are no or not sufficient openable windows and doors, a purge extract fan needs be installed into the room.

This fan needs to achieve at least 4 air exchanges per hour. In Scotland the volume of the room is capped at 3m height.

The extracted air needs to be discharged directly to the outside.