TOPIC: water heater/space heat combo

Hi all.  I inspected a home that had hydronic baseboard heaters, heated by the water heater that also supplied the potable water.  There were cold in/ hot out lines for the potable water and cold in/hot out lines for the space heat.
The seller made a disclosure that the potable water is used for the space heater as well.  I think he is incorrect but I wouldn't mind having some expert opinion on this as well.  (Tomorrow I am planning to call the manufacturer, GSW.)
I am aware of systems that have no separation between the two but they have to have a provision that allows the water in the space heater to recirculate to prevent stagnation.  That works fine if the lines go to an air handler but if the water has to circulate periodically through baseboard heaters, it would automatically heat the home some, even in the summer.
Aside from that, systems that do not have a separation between potable water and space heat water would not have two sets of lines going into and out of the heater would they?

Eagerly looking forward to any reply,
Thanks.