I do around 80 on and 70 with lights off, using 1 400w hps and 1 200w cfl, I plan to add a 3rd 600w hps but I know I'll need some cooling method by that point.... Fresh cooler air as others have said is great, but if you're in a hot climate you AC and vent your scrubbed hot air out of the room and have the AC and fans circulating your cool air. Bringing in air from outside when it's 100 degrees wouldn't do much better but if you live in a northern climate or cooler climate area than the cooler air would do wonders.