Open - air pressure from the fan opens the flaps, and allows air through the shutter.
Closed - Once the fan is off, no air (or light) can pass back through the shutter.
The spring operated flaps close when there is no positive air movement, preventing any air back-flowing when fans are turned off.
- Galvanised sheet steel housing
- aluminium flaps
When installed, the back draught shutters need to be positioned with the hinge area vertical, as shown in the image above.