I am remodeling an old 2 story house, and am installing 4 baths, 2 up and 2 down, 2 above the other 2. I want to install only 1 fan for all 4 baths, in the attic. Is this practical? If so, what size fan and motor should I look for? I'm thinking of venting it thru the roof, before I have the roof redone.