They also fit directly into the existing window opening and are available in many different sizes. Before installing, repair damage to the main window including replacing cracked glass or painting and mending damaged wood around the frame. Buy the replacement window to fit your main window. To ensure you are buying the correct size, measure the old storm window or the existing window opening. Since the storm window attaches directly to the window stop, it should be approximately the same size as the main window.
Test fit the window to make sure it is the correct size before installing.
Using an exterior grade panel adhesive or caulk, apply to the outer edges of the window stop at the top and sides distributing as evenly as possible. It is not necessary to apply adhesive to the bottom edge until the storm window has been installed and fastened. Predrill pilot holes, which assist in fastening during installation. They should be drilled about 12 inches apart and centered directly over the window stops. Press the storm window into the opening, pay close attention to the side stops and make sure to center the window between them.