I am fixing a poor installation of a bath vent fan. The vent cover outside
has the flappers that close (somewhat) when the fan is not under pressure,
but when the wind blows in the winter, it still pops open sometimes and cold
air gets in. Not pleasant to walk into the bath after a windy winter night.
It is 4 inch round vent pipe, and I'm wondering if there is anything like an
in-line damper that works the same way- backflow of air is blocked by a
flapper in the pipe, but when the fan is on, pressure going out pushes the
I'm open to any and all ideas, even if it means changing the 4" in the
middle of the run to something else. I just want to reduce/eliminate the
backflow of cold air.