Solar heating systems are provided which utilize an integrated fixture for transferring heat from a solar collector to a lower-temperature loop, e.g. a domestic hot water system or radiant heating system. The fixture provides a heat exchanger for transferring heat from the solar collector to the lower temperature loop. The fixture may also include a casting, in which are formed solar collector supply and return ports, lower temperature supply and return ports, a solar collector pump volute, and a lower temperature pump volute. The systems also include two pumps, and a temperature optimization control that varies the speed of at least one of the pumps depending on the temperature of the liquid in the solar collector.