ok for exchanging air in the room itself I was planning on atleast 1 4" passive intake hole in each wall except the wall that will have an exhaust blower mounted up by ceiling. he intakes will be made out of pvc plastic elbows to keep light from going in and will be putting pantyhose over the pvc opening to deter bugs from trying to enter. cfm size I am still debating, room around 12 x 7 x 6 1/2.