The vent flaps are completely closed and the flange is caulked to stop air infiltration. If cold air comes into your laundry room through the dryer vent, you should be able to stop it fairly easily.

Once the interior and exterior ducts are clean, reattach the vent pipe to your dryer. Check the duct thoroughly for any holes ...

A dryer vent with a loose or broken flapper invites drafts and mice into your house. When clogged with lint, vents not only ...