I wrote:
> You mean, the cell is a torus? With the cooling water flowing through the > middle? > The problem with that would be: Why bother putting the copper shell around the steel cell? If it is a torus, you can dispense with the copper shell, and put the heater directly on the outside of the stainless steel cell. In the 12 kW tankless water heater, the two electric resistance heaters have a torus shape, with a copper pipe running through the middle. - Jed
