Well I got my exhaust fan off of an air hockey table. It's a squirrel cage fan and it moves alot of air. It's probably a little louder than most the other squirrel cages you can get from a hydro store but hey it was free. Right now I have that fan with 2 4" passive intakes with a filter over both and 4 cfls and it's staying right around 74-77 F. Basicaly the temp of the room it's in maybe only a couple degrees warmer. I have a 400w hps on the way so I'm not sure how much the temps will jump when I put that in. Oh my cab is 4x4x2. So That's one idea.