Abstract: Several alternative forms of construction are disclosed, for enhancing build-up of solar-generated heat into a building or part thereof, while the sun is shining or the outside temperature is relatively hot, and for minimizing heat loss from the building when the sun is not shining or the outside temperature is lower. In the preferred form of disclosed construction, a member which is blackened for maximum heat absorption from the sun's rays changes its shape when it becomes heated, and acts as a valve, opening up for maximum inflow of solar heated air when the sun's rays fall on the blackened surface or it becomes heated from surrounding air, and closing when the temperature falls or the sun's rays no longer heat the blackened surface, so that flow of warm air to the outside or to a colder surface is halted, to minimize heat loss.