Fan-Tastic Vent Fan Vent with Reverse & Thermostat 5000RBT
http://www.google.com/products/catalog?hl=en&biw=981&bih=661&q=thermostat+controlled++exhaust+fan&bav=on.2,or.r_gc.r_pw.&um=1&ie=UTF-8&tbm=shop&cid=6305711225766269537&sa=X&ei=9ZULTpXJHMLcgQemk9ySAg&ved=0CFgQ8wIwAA
I am thinking of...