Building heating with a domestic water heater

Milenius

I want to do summer heating with a domestic water heater. I plan to use a double wall heat exchanger to transfer the heat from domestic water to the heating hot water loop. Since most commercial water heaters don't have taps on the water tank, I plan to use tees at the inlet/outlet to the water heater.

Is this possible? What sort of valving arrangement will I have? There is also a domestic water return loop.