Abstract: This invention is directed towards a low-cost solar heating system, or apparatus, which has substantially increased energy efficiency over fixed flow systems. The apparatus of this invention includes a closed flow system including flow lines for fluid such as liquid or air, to and from a solar collector panel, flow lines from the solar collector panel to storage means, and a circulating pump in the system for circulating fluid from the storage tank to the solar collector via a pump supply line. The preferably fixed-flow circulating pump is actuated by a thermally responsive switch set at a predetermined temperature setting, for example, 100.degree. F.