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:
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.
If a habitable room is internal, without openable window, this room can be ventilated through another room, but not a wet room. E.g. this can be the case if a conservatory has been added in front of a living room.
In this case the purge ventilation provision needs to be based on the floor area of both rooms.
The Zehnder LPID100 purge fan comes as a wall or roof installation kits.
This fan is suitable for rooms of about 12 – 25 m2 floor size. To calculate the purge ventilation requirement, multiply the floor area with the room height (max. 3m in Scotland) and multiply times 4.
The unit is manually controlled by the SDC1 superduct speed controller.
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