By oversimplifying the problem I have, imagine that I have a panel constructed of stainless steel flat walls. The dimensions are 80 in x 70 in x 20 in, and the thickness of the panel is 1/8 in. Inside, I have a heater that outputs 400W of convective heat. The temperature inside the panel is 50F, and the ambient temperature outside the panel is 0F. Questions: a) Assuming the panel is leak tight, what is the heat transfer rate through the walls of the panel? b) Newton's Law of Cooling states that the wall surface temperature is assumed to be the same as the inside temp, but won't the steel surface be colder than the bulk temperature inside the panel? c) Where does thickness come into play? I only see that variable in the conductive HT equation. I get getting WAY too high of a heat transfer rate. Any help would be greatly appreciated. Thanks!