I chose a Simaudio pair of monoblocks based on their sound and their cool-running temp. Mine were the W-10's - they had 750W/ch into 8 ohms, 1400 into 4. If you really cranked up the music, they would start generating some heat, but compared to a Krell or the Ayre I have now, not even close in terms of heat generated.
I don't know if this holds over their whole line and/or their newer models, but I could leave the monos on all the time in a medium-sized, enclosed room and not have issues.
