To prevent cold air feedback when my dryer is idle, I tried (temporarily) adding a butterfly damper to the vent conduit (inside, right next to the inner side of the wall vent). It functions perfectly. But over time will it collect enough lint to block the air flow and/or be a fire hazard?
I live in a very cold climate. There is no exterior flapper on the wall vent, and I don't think it would be safe to have an external flapper, as the vent is 12 inches above ground but the snow often rises 24 inches above the ground. (The dryer exhaust melts the snow for over a horizontal radius of about 12 inches or more.)
The butterfly damper was sold by a hardware explicitly for use with a dryer, but I don't know for sure whether it's safe over the long term. I received a suggestion to replace my (exterior) vent with a mushroom vent (which I'm not sure is available here) -- would the heavy snow clog up a mushroom vent?