I have the same problem mikey05 with the new house and cold air coming in through the fireplace, most notably the lower grate. I see the solution you were seeking wasn't found here so maybe my request will lend support to someone suggesting the best way of stopping the draft when then unit in NOT IN USE. I too am surprised a damper is not installed in the unit that opens when the unit IS IN USE. I'm frustrated as well since six months out of the year I have a towel or rug shoved up against the lower grill to stop the cold air flow. Of course, when we sparingly use the unit, this is removed; but, I can't feel satisfied with this solution. Have you found a solution yet?