An improved method of installing a storm window in a prime window includes application of locking clips at predetermined locations around the frame of the prime window. The storm window is positioned over the prime window and swung into place, whereupon the storm window frame snaps and is locked into place by the clips. Bulb seals around the storm window frame compress between the storm window frame and the frame of the prime window to insure a complete and reliable seal against the elements and maximize sound abatement.