We have a room in our rental home that was an addition to the original house. It contains our washer, dryer, a small closet, and our 2nd (half) bath, and a door to our driveway. Seems like it is completely uninsulated, once measured 20 °F than the room next door. (60 something in the kitchen, 40 something in the adjacent cold room). Anyway, there's a opening that's as large as a regular size door between the cold room and the kitchen. We stuck a tension rod in the frame and put a very thick cotton curtain in the doorway. It works wonders.