I have a 20 gallon with 175 watt MH
and 110 watts PC
lighting. It has 2 fans one pulls air in blowing over the bulbs and the other side pulls air out. The tank sits with one end facing a window. In the window is a double fan that pulls air in, acutally its a pretty slick fan, has thermostats so if it suddenly gets cooler the fan shuts off. Right now it is about 72 outside, 83 inside (room gets brunt of afternoon sun) and the tank is a cozy 81.7 with the lights on. When the lights go out, the tank actually gets warmer to about 82.5. When it gets to be like 85-95 outside, I will have the central air on to help.