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

According to Pass they idle at 600 watts.
I'm not an engineer, but my research translates
600W to 4,000 BTU. What have owners experienced?
That idle figure gives about a 150 watts of class A continuously. I have a pair running at this moment as I write. They are breathing sublime life into the toughest speaker load known to audio. The blue back lit dial is resting quietly in it's customary ten o'clock idle setting while the music flows at 70 to 80 hertz, my comfort range.
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 ?
Think about a block of metal that's 19x12x22 inches that is hot to the touch but not so hot that you couldn't keep your hand on it. This is in your room radiating heat. For a typical listening room, this isn't terrible. Then there would be two for stereo. Another way to think about it would be to imagine a lightbulb array of comparable wattage -- the great majority of a light bulb's wattage is radiated in heat, not illumination. 600 watts of heat from an X600 would be like six 100 watt light bulbs. (Or one 150 watt light bulb, per the wattage cited in the above posts.) Notably, the heat radiated might actually decline very slightly as you turn up the volume, so long as you stay in class A mode, since more of the power draw would be consumed in making sound. Of course, it might get a teensy bit hotter when you start peaking into class AB. The X600 is a fine amp. Good luck.
to heat.

Conservation of energy. The energy is always there, though the form may change.

Draw 600 watts of electricity in an amp and 100% will be converted to heat. Even if some is used to produce sound, this sound will degenerate into heat as it is absorbed or otherwise dissipated.
What's your electric bill like running these babies? and without?...
In a house with 62 light bulbs, all of which are left on too much due to kids, the initial extra cost of the monos was absorbed without raising WAF ire, and that is a good thing.

All of the 600 watts are lost to heat when not running. I suppose, at peak 1800 watts, that too eventually winds up as heat. The speakers are huge radiators.
The heat sink temperature on my 600's is about 114 degrees Fahrenheit at idle. The amps contain a thermal cutout that will shut them down if the heatsink temperature exceeds 167 degrees Fahrenheit. This is considerably cooler than the heat sinks on my old Aleph 1.2 amps.
Ah! and thus the 200 fully class A watts XA housed in the formidable X - 1000 chasis. This should give pause to owners of the trim mega watt "class A" amps that abound.
0ops ... 4,000 BTU was for a PAIR of X600's idling at 600W each.