This can be made to work one wall can be made as radiant heater that can make some difference to air temps. there are two issues radiant heat tends not to heat air but objects these objects heat the air. It is a very inefficient method it can work. I would suggest that the bigger issue is the tub itself, they simply do not hold heat in at all. Very poor insulators, sometimes adding insulation can be effective as well. I would suggest that this will require the use of a proportional t-stat as the snake can easily contact the wall and during an on cycle the temp cane easily be in the 160º range with an on off system.