Is 24 inches enough space for this class a amp?

Get on Amazon there are small fans you can get for audio that are quiet and can just leave on or put a temp controll device on them.25$each run off 5v USB or the back of many amps have 5v power out back for that. With this it does not matter if you forget and leave it on. I have several and my krell keeps cool under full volumn.heat is the enemy of most things. In pure class a the transistors run full power all the time and that generates heat but that's why the sound good. Enjoy the cool music.

+1 @mark200mph. I use these for my Pass.

https://acinfinity.com/receivers/

And maybe play some "cool" jazz. 😀

Yes cool jazz and ac infinity a match made in heaven

I think you have enough open space

it wasn’t playing music, just on, tubes warm, not blasting bass

you could buy an indoor/outdoor thermometer and watch the temp change in two locations, learn something.

you have a plenum/concealed space above the sheetrock. you could install a very quiet exhaust fan (they are noise rated) with a short piece of insulated ductwork, separately switched, independent of the hvac, any time just slowly/quietly move/transfer the hot air above that area of the room to the space on the other side of the sheetrock

use a switch that lights up when on, my office exhaust fan is so quiet, I leave it on sometimes. It needs a damper that automatically closes when off. not a cheap bathroom exhaust fan, a low volume, low speed, low decibels, and a short piece of ductwork with insulation for sound.