I currently have 3 different enclosures set up. I have undertank heaters on all three, appropriately sized per the instructions. I’ve heard that the risk with these is they can make enclosures too hot, but I’ve only experienced the opposite.

Without overhead basking lights or ceramic heat emitters, the cage temperatures stay in the 60s during the winter, when I’m at work and the woodstove isn’t running. In the summer when I don’t have a fire going, the cages stay pretty close to room temp, again only if the overhead heat is off. My enclosures are all bioactive, with live plants and 2”-3” of substrate, no drainage layer. So I have to keep the BP’s heat emitter constantly on with a thermostat. My emerald swift is a high elevation lizard, so she actually does quite well with the basking light on a timer.

I don’t mind relying on the overhead heat with screentop cages, but I’d like to turn a few 10gal aquariums into vertical uprights. Overhead heat won’t work through solid glass.