Dave D. wrote:
Just watched the video, now I get what is meant by the OP's use of the term "recirculating." He is describing recycling cold water back to the main tank. To me, I was thinking "instant on" recirculating hot water, which creates a loop from and back to the hot water tank, which is driven by a recirculating pump, different than the main pressure pump. This loop is always heated, and when a hot water fixture is used the pressure drop in the loop turns on the main pump which actually provides the driving force for water to come out of the faucet.
This would keep the hot water from freezing; the back-to-main-tank loop would not. With properly insulated lines it should not pull too much extra duty from the hot water tank. This is how it works in my house -- even in rooms farthest away from my boiler/hot water tank I have hot water right away.
That works great in a residential application but in the RV, I only want the pump to run when needed, not constantly. Battery conservation. I only need 6 seconds of run time on the pump to get hot to the sink. A residential setup has a recirculating pump that runs all the time, at preset times on timer, or at a set temperature. Typically, the loop is taken from the last fixture in line and so should the return line in this setup. My pipes are all insulated and have 1" foamboard plus the TC wall insulating them from the outside in cold temperatures. The pipes are also run together with insulation tube over them and the heater vent hose next to them. The pipes are pretty well protected from freezing.
