how big is the air gap between the floor and the rack. It helps atleast up here due to the fact that floors can get cold in the winter. i have about a 5 inch gap between the rack and the floor. casters and bottom of the cage. i have one rack with 3 different size tubs in it. I guess when i built it i was smarter than i thought. I have 4 41 quart tubs on the bottom 6 27 quarts above that and 16 hatchlings on the end of the tape. suprisingly enough i have a difference of 2 degrees in hot spots on all the cages and all my cool sides are at 82 degrees. i don't know how i did it but its awsome. i bet i could build the same rack again and not have that kind of luck. my snakes move better in the new rack than they did with the old rack. i moved 3 snakes from aquriums into this rack. kind of the reason i built the rack to begin with. They all seem happy. Im running it all on 4 inch 6 watt tape and a cheap rehastat. i keep telling myself that i should get a helix or something for it but i think it might mess up something good that i have going