That temp sounds about right due to the F@h and the room temperature. The upper left hand corner (looking at the iMac from the front) is where the power supply is. It is normal for it to get very warm/hot in that part of the enclosure, especially on the top and rear.. The fans are located at different parts of the iMac - mainly where the CPU, hard drive, and graphics card are. The power supply heat vents out the horizontal slot across the back, along with the exhaust from the fans.
I would guess that if the temp of the room dropped by 5-10º and you paused the folding overnight, it would probably be cooler to the touch. I can verify that it is still within the normal range and spec and should do no harm. The fans will kick up if they are needed.
If you had Temperature Gauge Pro, you could manually adjust the fan speeds to a higher RPM to cool it down...at the expense of noise.
C