I had a thru the wall Panasonic fan installed in my bathroom back in Sept, since there was no ventilation and I didn't want the mildew problems that the previous owners had. ( just bought the house in May, and the bathroom closet had a lot of mildew.) Now with winter here, when it's cold and windy, I get a draft from the fan. If it's REALLY windy I can see the flap opening to the outdoors! I really like the fan, it's efficent and quiet (which is why I chose the Pansonic) but this has me worried, with heating bills as high as they are. And...it's a tad drafty in the shower if I run the fan while showering! Any suggestions?