An air temperature regulating assembly is provided having a packed rock bed through which air may flow between outer and inner spaces by way of interstices between rock units in order to transfer heat to or from the rock bed, in use. Dampers control the flow of air between the outer space, the inner space, an enclosed air space the temperature of which is to be regulated by raising or lowering it and the surrounding atmosphere. A fan moves air within the assembly. The rock bed is in the form of a pile of rocks having an upper surface that is inclined and directed in the general direction of the sun to directly absorb solar energy. The outer space is defined between the upper inclined surface of the rock bed and a transparent cover spaced upwardly from the surface of the rock bed.