Amps and Kimber 12tc. Big amps and room temperature.

All you have to do is look at the power dissipation. Get a cheap device like this one:

https://amzn.to/3a6NN4P

It’s all about how many AC watts you are putting into the room. 100% of that becomes heat. Best analog to this is to think of incandescent bulbs.  Remember how hot a 60 Watt bulb would get? 

I doubt that 12TC’s rather high capacitance is bothering the Bryston enough to result in extra heat.

There is always some heat from a power amp; as Erik said, whatever power it’s drawing winds up as heat. The B3 series runs cool compared to some of the competition. I tried a Pass X250.8, which puts out 400 watts of heat at idle -- as much as the heater I use to warm the audio room in the winter.

If the heat is a problem in your room, I suggest you look into some of the newer Class D amps. I’ve heard great sound from them, and they run cool.

P.S. I had a 14BSST, and loved it very much -- except when I had to move it.

I finally had 2 more lines run from my main duct work into my music room. It is much cooler now. With the amp off it was 61 this morning and with it at idle 68.

Congratulations on fixing it.