It's not a Pass but I have a Krell KSA 300S that puts out a lot of heat when I'm playing music loud. At idle it's warm but after an album or two at 95 dB it's too hot to touch. At idle the amp uses around 400 watts. I only turn it on when I'm going to listen to music.
I am lucky to live in the land of cheap electricity (central Washington state) so this has not been too much of a problem. We get fairly cold winters so the heat in winter is welcome but it also gets hot during the summer (100+). During the summer I'm careful not to run the amp for any longer than necessary. It definitely makes the room warmer and the heat pump has to work harder. I've listened for any sound difference between startup and 1 hour later and it sounds the same to me.
I'm thinking about upgrading at some point to a pair of Pass monos. If I do this I would go with the Class A/B line partly due to the heat and partly do to the lower cost. There are a lot of very expensive amps out there that are Class A/B and I believe that we are at a point where the sonic advantage between Class A/B and Class A amps are minimal. I'm running low sensitivity/low impedance speakers so I'm going to have to go with a big amp that can put out at least 200 watts and handle low impedances. A Class A amp with this capability is very heavy, hot, and expensive.
@devinplombier I have a Krell KRC2 that also has no on/off button. I'm the original owner of this preamp and it has remained on all of its life. I had it recapped a few years ago and it's going strong. It's Class A and it's fairly warm when idle. When the shop recapped it they raved about it and said it was one of the best designed and built preamps they had seen.