Back Draught Shutter

A backdraught damper sits between the fan and the outlet and lets air pass one way only. The blades are pushed open by the airflow and drop shut as soon as that flow stops. Available from 100 to 250 mm.

This is about what happens when the fan is off

An extraction system is always calculated on what it does while running. The hours it stands still stay out of view, and that is exactly what this part is for.

The moment the fan stops, your duct is an open pipe between inside and outside. What happens then depends on temperature. If it is colder outside, cold air sinks down the duct and you get draughts, a cold layer over your plants and a heat loss your heating gets to make up. If it is warmer outside, it runs the other way and warm air is drawn in.

Then there is odour. Everything left sitting in the duct and the silencer can simply travel back into the room on a reverse flow, or worse, into another room through a shared duct.

The damper solves that mechanically, with no power and nothing to set: pressure opens it, gravity and spring tension close it.

Available sizes

Technical Specifications:

• Action: opens on air pressure, closes at standstill
• Blades: aluminium
• Shell: galvanised steel
• Orientation: with the direction of flow, between ducting or rigid parts

Frequently asked questions

Does it cost capacity while the fan runs?
A little, since the open blades stand in the flow. In exchange your system leaks nothing back.

Where in the run does it belong?
After the fan, on the outlet side, and as close as possible to the point where the duct leaves the building.

Does it work horizontally?
Yes, as long as you follow the marked direction of flow. Vertical with the flow upward closes fastest.