Here is my last post on that sublect:
This is going to be my final post on this subject ... maybe.
At 7:00 AM with the air temp at about 27 F and I will assume the overnight temps were a little lower, my tub is at 84 F.
My conclusion is: my tub, an Artesian Cayman, a full foam tub in temps ranging in the 20's to mid 30's, will hold it's temp above freezing for at least a week. It dropped 18 F in 64 hours (about 2 1/2 days).
Other thoughts: NJDave with A LOT more experence than I stated about temps above and below the seating area and I will say that I agree to what he said.
A couple of things I would like to point out about my tub and NJDave or anybody please feel free to shoot holes into my therory ... this is how I learn.
My tub does have tubes that are off the circ pump running to all the pumps (I don't know about my 3rd therapy pump though) that keeps the water above freezing by circulating some water into the pipes. My tub clears it's water from it's pipes every 12 hours so it would exchange the water in the plumbing with fresh warm water unless the water in the pump frooze. I believe my tub gets a little boost from solar heating as it gets about 7 hours of winter sunlight whenever the sun shines.
I now have the piece of mind that IF my heater goes out and it maintains electric, my tub will not freeze solid.
OK, I'm done!