I remember very vaguely, when installing a water heater that I read something about using the water heater as the water heater for the heating system. Where can I find manual or how to do that?
Thanks

Its normally the other way around. Hot water heating systems can be set up to provide hot domestic water via a heat exchanger. This is not something easy to do once you have completed putting in a new water heater. This would have been an alternative to a newwater heater.