There is more heat, at the bottom. I've seen a little browning of the insulation in my 1, 2 and 3; but it's not enough to worry about. With the "D" models, the only part that gets hot is the SSR. Same as the standalone Auber, but it's contained in the housing. That's why the heat sink is on the bottom, and we use the legs to elevate it for airflow. The controller box, on the D models, doesn't get hot at all.