Yeah, my reptiles need the heat more and to be kept more steady than my dogs, but if it weren't for the dogs I'd turn the thermostat down when boyfriend and I leave for work and let the snake room operate on the electric heater, which does an effective job in that upstairs bedroom, to save on gas, so there's that. More so, though, the dogs need air flow/cooling in the summer. Boyfriend keeps corns which are native, so as long as there's a breeze through an open window they do fine in the summer, and my ball python collection only struggles with the humidity during that time. We still have to run either a few fans or an AC unit for the dogs when we're not home in the summer, as our double-coated breeds (husky and german shepherd) don't tolerate the 90-degree weather well. The argument could be made both ways then, as far as electric and gas costs for maintaining endotherms vs. ectotherms. From a sustainability standpoint, I think a higher percentage of the product I go through for my reptiles is ecologically friendly compared to to dogs. Soiled wood shavings can be easily repurposed as mulch or compost, and I go through less plastic buying bales of aspen for the 50-ish snakes in the house than I do for the two dogs and two cats buying 35 and 20lb bags of food.