Insulate the heck out of the house, it is cheaper to keep the heat in than to replace it.
We keep a small chest freezer for frozen mice/rats/rabbits in the snake room. The exhaust from it helps warm the room. In the winter we close the door to that room, in the summer we actually have to keep a fan going to blow the air out as otherwise it would get too hot in there.
Use well-insulated enclosures made from melamine or PVC that are designed for reptiles.
Racks can be covered with a blanket to help keep heat in the tubs.
We also have a generator as it's common to lose power due to downed power lines during ice storms.