I would go more like 4" hole. You can get a 4" duct fan for $20 -$30 at home depot in the attic fan section, but you'll have to put an electrical wire on it. Some flexible 4" clothes dryer ducting and your all set. also look at the flanges you can get for dryer venting they screw right on makes it easy. Also if you want to regulate the temperature you can get a thermostat that will mount right inside the duct or box for another $50. :thumbsup: