Consttraveler, 1 MINOR correction....
Agreed....warm yes / hot no.
BUT While it IS true that 'The amount of heat generated is directly related to the electrical efficiency of the device.;
it is ALSO true that the gross power input is also a factor.
Something drawing 100 watts at 90% efficiency will run cooler.. (actually, generate LESS heat) than another device drawing say.....25 watts and only 20% efficiency.
You can have a very inefficient device...a Class 'A' amp, for example, drawing a fair amount of idle current, which is all heat, but the temperature is fairly low due to huge heatsink mass. You may be able to heat a room with it, but you'll perceive it as 'warm'. Cut the heatsinks by half and it'll cook, while generating the same amount of heat.