Watts to BTUs?

Vmk, 1 watt delivered over 1 hour produces 3.414 BTUs. Amplifiers produce the most heat, are no more than 50% efficient, and tube amps operating in class A are the most inefficient. A 100 watt per channel class A tube amp probably generates 400 watts at idle which is 1366 BTUs.

V, The heat generated by your gear varies with too many variables to count. The general recommendation is to exhaust this heat. If your HVAC guy needs you to do calc work, you have the wrong HVAC guy...