We've just had a new range hood installed, vented straight out the back through an 8-inch diameter duct, with a new wall cap with spring-loaded backdraft damper.
When it's the least bit windy out, the damper flaps and bangs. The sound is maddening, and the flapping allows cold air in (or warm house air out, maybe).
Our electrician tried to increase the tension on the spring without affecting the damper's ability to open at the lowest fan speed. Yet it still flaps, and sometimes the damper just stays ajar now, and cold air really does pour out of the range hood into the kitchen.
There's a critter screen on the bottom of the wall cap, so there can't be animals moving the damper.
Why does the damper flap? Is it possibly the shape of the wall cap (triangular, not rounded on the top)?
What can we do to prevent the flapping? Any ideas or suggestions?