superseaanswered grow question 2 years ago always go for an extractor and make a vent for fresh air. the displacement of the extractor putting air out will force fresh air in. if you do this oppositely and force air in there is no force to push air out. this is how my room is setup one big extractor throwing air out from the top of the room and a passive (no fan ) intake on the bottom of the room this makes fresh air come in from the bottom circulates under the plants and extracted out from the top :) hope this helps