Heating it is an unbelievable pain. I keep my house very cold and the Critter Cage is all glass with a screen top so the fluctuating temps of the house is a big factor on the temp inside the Critter Cage. To heat the tank I am using an UTH and an ESU Reptile Bi-Light (20 inch) that holds two lamps (product description here) that I can use to adjust the temps. The most I’ve had to use was two 75w bulbs (humidity killer), the least was one 50w. My limited knowledge of thermodynamics gave me the idea of extra thick substrate, a background on three sides, and as much “stuff” in the tank as possible, which as helped to stabilize the temps a lot. I have also used different things to cover the screen top with varying degrees of success. I think one I get the Plexiglas in (ruined the first one) that it will be stable enough to trust a thermostat with.