You can use another uth and thermostat for the rest of the tub and set it so it's around 80 under substrate, I have used this method for 3 snakes and currently still do with 1 (rest switched to rhp) and I have not had any problems and my house stays at 60-65 all year around. Plus using another uth for cool side would be cheaper than running a space heater. Make sure you are taking the temp of your uth under the substrate right against bottom of tub over uth and that it is no hotter than 94 but 92 would be better so you have wiggle room, if your using paper towels then set it so it's 90 under the paper towel.
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