How hot do a pair of Pass Labs X600 amps run ?

600 watts converted to heat would produce just over 2000 BTU/hr.

Don't know about the conversion, but surely not all of the energy is dissipated as heat. However, if they are Class A 150 wpc, I would imagine they run pretty hot, unless the heat sinking is very extensive.

The 600 white papers say 150 watts. They act like there is more. The heat sinks are huge, and do get good and hot. Each amp weighs in at 150#.

As long as the heat sink temperature is not excessive, say above 120-130 deg F, it's normal for a pair of Class A amps to run warm enough to heat the room. When I run mine all day in the winter, the rest of the rooms in the house drop 10 degrees since the T-stat is in my listening room.

I have an X350 that I leave on continuously. It's roughly the same as one x600 monoblock. The top is slightly warm but the heat sinks are usually around the 'mug' temperature of a 3-5 minute old cup* of coffee.

I would say that it generates

A) Less heat than my ARC VT-100, old Aleph 2's, and likely
my BAT VK-5i tube preamp.

B) More than my old 185 W McCormack DNA-1, 200w Ayre V-1x,
and all 100-200w non-aleph amps I have used.

C) Around the same as my 4 KT88 tube AES 25 tube amp, and
possibly my 2 300B tube Cary 300-SEI

* The cup is glass, 3mm thick, green. My employer's stunning interpretation of an inspirational and appropriate substitute for employee pay increases. Rather pretty.

** Actually one of a set. The other being utilized as a spit cup in the upstairs bathroom.

*** Now that I think about it, I am strongly considering migrating the first away from coffee duty, and into a new role as a receptacle holder for decimated shellfish casings. Opinions ?