I have a gas fired hot water heating system distributed to 4 zones, two of which are copper baseboard and two of which are cast iron radiators. The boiler water is heated to 160 degrees for circulation to all zones. Domestic hot water is via a separate gas fired hot water heater. A friend has a home with all new copper baseboard through 5 zones and a 6th zone which circulates boiler water through some sort of heat exchanger for domestic hot water. His boiler circulates water at 190 degrees. Is his water temperature too high? Is my water temperature too low? Any insights would be appreciated.