Telect has performed some heat dissipation testing on a number of panels including GMT panels, TPA/GMT panels, demarcation panels, and high-current fuse panels.
The actual heat dissipation will vary based on a number of factors including operating voltage, temperature, type of power panel, actual load capacity, and fuse size. In order to get an estimate of the heat dissipation, Telect recommends using the following formula:
At maximum rating of the panel, the power dissipation is ~0.40W/A.
This is caused primarily by the dissipation of power in the fuse holders. At small load capacities the multiplier could be as low as ~0.05W/A, as dissipation is exponential.
In order to convert the heat dissipation to BTUs, you can this formula to calculate Btu/hr:
Watts * 3.412141633 = Btu/hour