I might not be understanding you correctly but do you have the UTH inside the T8? If you do, it shouldn't be in there.

The UTH should be on the outside of the T8 on the bottom. That's how the HerpStat probe can sense the heat tape temperature and adjust it accordingly.

Personally, I only run RHPs in my terrariums and that's more than enough. However, where I keep them doesn't get that cold.

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