Abstract: A ventilator for a glass block window is provided that has a high insulation value, is simplified in construction, and is easily repaired. The ventilator includes a unitary frame arranged to be accommodated in the glass block window and a sash for selectively closing and opening the central opening of the frame. The sash includes a unitary sash frame, an insulated glass window assembly inserted into the sash frame through an open front side of the sash frame, and spring clips which releasably retain the window assembly within the sash frame. The frame, the sash frame, and the spring clips are each vinyl extrusions. The ventilator also includes a bubble seal at an interface between the frame and the sash frame when the sash is closing the central opening of the frame. The seal is integral with the sash frame and preferably is coextruded with the extrusions of the sash frame.