Tank Heater vs.Recirculating Hot Water

westend wrote:
Your math looks solid but establishing Delta T at 80f isn't necessary (unless you want the water in the fresh water tank the same as the water heater). To establish a continual temp of over 32f (perhaps 40f is a better target), you'll need to know the amount of heat loss at ambient adjacent to the tank and supply lines. Your experimental method of temp measuring in tank will probably bring best results. Off hand, if camping at 0f with cabin temps above 65f, with assumed fresh water temp of 40f, assumed tank placement and lack of total insulation, circulating hot water into the system a couple of times during the night should get it done.

West,
Thanks for the confirmation on the calculations.
I had no intent or reason to raise the temperature of the fresh tank above 40 degrees. The reason for Delta T was to determine how many BTUs would be transferred if the tank got to that temperature so I could roughly compare it to a typical RV tank heater. I don't know how many KW a tank heater uses, but I see that they heat the tank to a median of 54 degrees (cycle between 44 and 64 degrees).
My tank is insulated on five sides but the bottom only has a thin layer of corplast over it. So, of course, the water always has contact with all of the surface area on the bottom of the tank, which is also where the most heat transfer will occur.
I like your WAG (unless it is more than that???) of my only needing to run the system just a couple times per night to get the job done.
I guess that I'll just have to implement it and then wait until it gets cold enough to test it out.

Steve