Um my vet bills last yr would disagree with you!
In order for the ambient temp method to work properly you have to have a very tightly controlled room. Most do not have that much control over their room and have cold parts and such, on that case you do need a hot spot, perhaps not 90 degrees, but you do need hot spots, otherwise your keeping your snakes in the 70s and that will make them sick.
Also if you like feeding large meals this method may not work very well for either.
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