Yeah, for supplemental heat, an RV owner with forced air furnace might choose a different appliance. I already have a different appliance, a propane fired heater that is vented and uses no electricity.
I'm also thinking of this as supplemental heat rather than the main source. My goal is to bring the fresh water tank to an equilibrium between ice cold and room temperature. At the same time, I could be drawing a bit of supplemental heat from the system.
I was worried about any type of adverse conditions ensuing from using the potable water in a heating situation like mentioned. Roy B has the closest application to what I envision.