I'm going to use it where my torts sleep in my shed. during the summer when it 70 at night it was a good 95+ in the shed but its now gets down to 75-65 during the night in the shed which is way to cold for my torts.
For which species do you want this? Your russians are fine at 65-70. If you want to keep the sulcatas out there you'll need to make a big insulated closed chamber.
I have two of these in my garage. They are wrapped in 1.5" rigid foam, except for the fronts, and they maintain 80 degrees all winter long with a couple of CHE's on thermostats. My overnight lows drop into the high 40's during winter in my garage.