I have 5 sulcatas that live outside all year and this year we are having what I would call a normal winter. Temperature's have actually been below average, a few days straight below freezing with a low of 19F last night. I've been keeping track of the wattage being used to keep them warm for a couple weeks now. For all 5 house's it's been around 575 watts on average. Some using more than others. I don't use separate thermostats everything is on rheostates. This way the wattage use is constant and not fluctuating up and down. 2 of the houses have a Stanfield heat mat a chicken brooder heater from Tractor Supply and as small electric oil radiator heater. One has a Stanfield mat a oil filled heater and a CHE. One has a Stanfield mat a a couple heated tiles that I made. And the last one is heated with just my home made heated ceramic tiles. The inside temps are reading at this moment 86.9, 85, 86,7 85, 91. I feel that the proper insulation and layout of the heaters is what helps my system work and keeps the electric use low and affordable.