I agree that flexwatt has plenty of problems, but at the time that was the best thing available. The first rack I ever built was heated with hot water (Melanine shelves with a groove routed for 3/4" vinyl tubing that was hooked up to a small pump sitting in an aquarium that was heated with an aquarium heater. Hot water from the aquariumm was pumped up to the top shelf and drained back and forth through the rest of the shelves until it drained into the aquarium again) It actually worked pretty slick but I was never able to get it very hot. Worked okay for corn snakes though.