stinky is correct in saying to cool the room at night(windows open), then let it the room heat itself up during the day (windows closed) if you leave the windows open it'll get nearly as hot as outside air (rather quickly btw), it won't if the windows are closed when its hot out. I cool my garage at night (with fans) then shut the windows during the day (so the growroom sucks only from the cool garage that is already cool from the night before and the cement floor) some days it makes a 20 degree difference between outside and inside. no reason to take down the 400 watter! just be diligent!