According to the caresheet (which you can find here):
http://ball-pythons.net/forums/showt...s%29-Caresheet
it should be between 88-94*F. I keep mine around 91*.

What I did with mine was I foiled and taped the entire top of my screen cover and I left a square about 6"x6" or so above the cold side, just big enough to fit my CHE and for air to circulate. I also didn't use the foil tape, I used HVAC duct tape (which is duct tape made specifically for air conditioning purposes i.e. ductwork and whatnot). I don't know if that would make a difference, though.