It really depends on your room temps and how stable the temps stay. Back heat heats up the air so it has to be set higher than belly heat. Belly heat just provides that one hot spot.

I originally had a back heat rack with a single piece of 11 inch flexwatt running behind it. It worked out great. It provided the perfect temperature gradiant. The air and space closest to the flexwatt was 90 degrees and the cool side was a nice 80. However, my room only stays 75ish. In order to achieve the 90 hot spot, my flexwatt ran like 120 degrees. I switched to belly heat because of this. According to the manufacturer, Flexwatt shouldn't be used over 100-105 degrees. And Rich from Reptile Basics have pointed out certain potential dangers when it exceeds recommended temps for extended periods of time. It also shortens the life of flexwatt. (Its another thread here with the title "flexwatt over 100?" Or something similar. Can't remember the exact name)

Once I changed to belly heat, the flexwatt no longer has to run as high. I currently have it at 95 to achieve a 90 hot spot in the tubs. The reason being because its not solely heating the air temp to provide the right hot spot temps.

Thats just my experience with back and belly heat. I like back heat more, but for the safety of my home and animals, I didn't feel comfortable running the flexwatt that high to achieve perfect tub temps. Like I said before, it really depends on your room temperature and how stable it is.

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