I'm not 100%. I was reading something the other day on here. Very thorough. If I can find it I will edit and post a link. With passive intakes though, you should be fine. The amount of air coming in naturally through 1-2 small passive intakes would probably not match the power of an active exhaust. Like Fresh said, you want air to linger for a bit, while also constantly re-circulating fresh air. The real problem lies in an active intake and active exhaust. If the force of the exhaust is matched or exceeded by the intake, the air will be pushed out before the plants have time to utilize it. Again, I am no expert... and I'll try to hook it up with some sweeet factoids. Keep :jointsmile: