I need to install a fan for ventilation in my first floor bathroom. I live in a story and a half home and there is a bedroom directly above my bathroom. I don't want to have to hack into too much to install a ceiling fan so I've been looking into the through the wall vent fans. my only concern is the model i'm looking into (broan 512m) requires a 6 inch hole to go through my wall and the only thing that is going to stop the cold air (i live in central Illinois) is the plastic louvered wall cap that came with the fan. My house is drafty enough as it is but this just seems like it would be the same as leave the hole wide open to the elements. Especially since the wall is facing my neighbors home and its only a driveway width away so i can guess the wind would tend to open the louvers.

Does anyone have any insight on how to go about ventilating my bathroom with a through the wall unit and the best wall cap to use or even how o keep the cold air out? Should i get one of those range caps that have the shield on them? they don't seem to close nice and tight as the vinyl does though.

any suggestions would be appreciated!