Abstract: Spaced exterior and interior windows define a solar plenum having communication with one isolated chamber of an adjacent dual chamber bay, the second chamber of which is in communication with the outside ambient or the inside building space air. Dampers for the solar plenum are automatically operated by thermally sensitive devices in the two isolated bay chambers, one of the devices controlling the direction of damper movement and the other device controlling damper actuation. The two dampers can completely close the solar plenum or vent it to the outside ambient for dissipating heat or to an interior space requiring solar heating. A solar screen in the plenum increases the thermal efficiency of the window arrangement. In a modified form, only one thermally sensitive device is provided which is in communication with the solar plenum and is connected to operate the two dampers to either completely close the solar plenum or vent it to the outside.