I use an under the tank heater stuck to the bottom of my viv. I put paper towel taped over it on the inside so that the snake can't lay directly on the heater if they burrow. Then the substrate goes over that. In the winter my house gets very cool, so I will use a heat lamp on the warm side to keep the air temp on the cool side in the 70's. Otherwise, the temps drop down into the low 60's. Some people live where it's so warm that the air temp keeps the viv pretty warm and you won't need anything.