I need to install a wall-mount bathroom fan on an outside wall so I can vent to the outside, and I'd like to use a humidity sensing fan for convenience. anyone have any recommendations? are there such animals out there? I've done some searching and see lots of choices. it's also in to an existing wall, not new construction, tho I'll be able to fish the power up in to the wall with no trouble. any watchouts on installing in existing wall? can ceiling mount units be used on a wall? I have 2X6" framing in the wall. thx as always!