I recently installed 2 Panasonic vent fans due to their extremely good ratings here on the forums. I noticed when I installed them that the door for preventing backflow draft has a notable gap all the way around it, and does very little to actually stop cold air from coming back into the room.

These were 2 different models, and both use the same type of draft door. Not only can cold air come in, but I would imagine that there is plenty of warm air escaping out these fans, even when they are not on.

Given all the interest in energy savings and keeping a tight house, how can the losses from these vent fans be considered acceptable, and what if anything is done to improve the situation?