I have the 40W in the middle of a 30" enclosure about 14 inches tall. the room is between 60 to 65 degrees most of the time. At 100 percent the area directly below the actual panel is easily int eh low 80's, on warm days i bring the power down a little bit, but there is a very definite line where the "footprint" of heat stops and the temp drops about 5 - 7 degrees. its sufficient for now b/c the tank and snake are small, but when its time to upgrade to a 4 footer i'm certainly going to need another 40w and put them side by side to maintain a comfortable overall ambient temp.