I have both back & belly heat in two different racks; I can't tell a difference between them as far as my animals go. Neither seems to have any effect on feeding response/digestion/overall health, etc. that I've been able to tell, anyway. The room I keep my animals in is maintained throughout the year with either heat or cooling to maintain the proper ambient temps overall but other than that, nothing is any different between the racks aside from how the Flexwatt is situated. I don't really have a preference either way between them and the one rack I purchased directly from Animal Plastics I got with belly heat; the other I bought used and it came with back heat. Do what works for you; pros/cons to both but either will work fine if used within the specifications it was designed for and with a thermostat or thermostatS to control the output/act as failsafes.