The entire bottom is covered with two separate heat mats one at 80 and one at 90 degrees ambient is 77 with my room temp at 78. Its adequate however I'm not impressed with tubs, at least in the sense they get tons if hype. It does keep humidity great but room temp is very important.
First picture, that tub never seen good ambient temps and was replaced with the second and although it's good the room is quite balmy.
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