[Marqed97]

I have a ventilator fan thru the roof in the crawlspace above my 3rd floor ceiling. There are vents at each end of the house, and the fan is pretty much dead center of the roof. My question is, what should the thermostat be set at? Is it more for keeping the 3rd floor bedrooms cool or strictly for keeping airflow thru the little space between the bedroom ceilings and the roof? It was set at 70, seems like it'll be running all summer at that setting. I'm in NW WI if location matters...it does get a bit humid here in the summer, temps top out in the 80's in august. Thanks for any info, never lived in a house with one.