Abstract: A solar energy system for heating water is disclosed. The system comprises a closed piping circuit in which water is pumped through a heat exchanger and storage tank which are not exposed to freezing temperatures up through a solar collector which may be so exposed. Protection against damage from freezing is provided by enabling drain-back of the water from exposed portions of the system and replacement with air when there is no water circulation.When water is circulating, a surge pipe bypassing the storage tank provides unimpeded flow of the full volume of water while extracting entrained air which is conveyed to the storage tank. Thus, solar-heated water does not flow through and is not stored in the storage tank during operation of the system, and the cost and inconvenience of insulating the storage tank in order to inhibit large energy loss is avoided.