Draft-Proof Bathroom Fan
Repairing or replacing a damper flap helps reduce drafts on a bathroom exhaust fan
What can I do to make my bathroom exhaust fan draft-proof?
Sandra, Toronto, Ontario
Tom Silva says: A bathroom fan is never going to be 100-percent draft-proof, but it could be that your exhaust fan has lost its damper flap. There is a passage that runs to the exterior of the wall, and as that goes through the wall, inside there's a little damper or flap that covers it. It's not very heavy, but it's heavy enough to keep a major draft from blowing in. When wind wants to blow up it, the wind actually pushes the damper
shut. But if that is missing, you are going to get a lot of air coming
back at you through that passage. Some dampers have louvers instead of a flap, but the same thing will result if a louver is missing or they aren't closing tightly. Either way, you should be able to repair or replace the damper relatively inexpensively.