Hi,
The 28's in the front open rack are stacked with a 7B-SST(center duty).
Use to leave them on 24/7 but my power bill was a tad up 40-60 a month more with 7bs.
Now I power up 15-30 min before listening,the 28's are bit warmer than the 7B-SST(even with the 7 on top).
I'll say the 28's after 4hrs or so are a comfortable warm where you can put your hand on them and its comfortable.
They don't heat up my 12 x19x7 room,I think if they did that they would need rebiased as I know how hot that can get(happened a few yrs back).
The 7B-SST2's are just for surround duty

,just cuz I always wanted monos all around.
Heat from the 28's,I wouldn't be concerned as I know I can have my hand on them for as long as I want and is comfortable.
My Vac tube pre is on 24/7 and she's warmer than the thre bad boys up front and can leave my hand on also.
I'll try a couple picts and you'll have an idea of how they are stacked ect:
