Abstract: An apparatus for the utilization of air and solar energy and for the recovery of heat, e.g. in a building, comprises a heat exchanger formed along a wall of the building structure which, on the one side, is heated by lost heat from the building and, on the other side, is heated by solar energy. Air is inducted to flow from the ambient environment through the heat exchanger to be heated by solar and lost-heat energy and then passes to a heat exchanger, preferably forming part of a heat pump, from the thermal energy of which air is recovered and used, e.g. for heating the building.