Abstract: A metal collector plate with black paint on its face is mounted in a heat insulated space with a dual pane transparent member transmitting solar rays to the face of the plate. The front face of the plate is spaced from the transparent member providing a passage for free flow of air upwardly along the painted surface. The back side of the plate is divided transversely for exposure to two air chambers, the lower air chamber receiving incoming cool air which becomes pre-heated by contact with the back side and then flows through suitable passages through the lower edge of the plate into the free flow passage, and the upper air chamber receiving heated air from the free flow passage through slots at the upper edge of the plate and additionally providing for contact between the heated air and the back side of the plate. A differential thermostat control for flow of air through the collector unit is operated by heat sensor probes in the cold air intake and hot air chamber.