:welcome: My grow room is 7ft Wide x 6ft High x 12ft Long. One 265cfm exhaust blower + 160cfm booster fan. One 265 cfm intake blower + 160cfm booster fan. One 400W HPS + Two 216W Fluors. Room is covered with Mylar. White floor. Have White Poly partition dividing room in half. Also have Six 9 inch fans for air circulation. Question? How frequent do I exchange air, and the duration of air exchange. Info from books contradictory and confusing. Want info from someone who "Really" knows a solution or answer. Thanks for your help. Greatly Appreciated. Happy New Year! Peace! Rock On! Smoke On! assit: Phant