i used 3 23 watt cfls and 3 42 watt and i used one computer fan and had no heat problems except for when the plants touched the lights they would get burned. Might have something to do with the room that the growbox is in was quite cold and i had a fan blowing cold air from outside towards the growbox. i dont think you should have heat problems if you use 2 computer fans, assuming you are not using the little tiny ones you hook up to a 9 v battery