Murdog,
I may not be the one to give you a good answer for this, but I set my old Coleman (6 person tub) on a low temperature until a few hours before each use, and it was not bad on electric, at all. I'm in an all electric home in a rural area and our rates are high, so if I could handle it, my bet is that you can, as well. Also, your tub is newer so I bet it is even better on energy use than my old Coleman was.