The design required that I move the hot water heater to a new location. I had a very well insulated 250 gal. water storage tank left over when a solar pool heating system was abandoned. The tank was extremely well insulated and in an interior room that was always at a comfortable temp as well, even with a good amount of fresh air ventilation. It was essentially free and the new tankless heater was the main expense. Aside from the case of beer for the bright plumber.