An "add-on storm" is suspended from hooks and held closed with a gate hook and eye. They are exchanged for screens in warmer months. A "combination storm" is screwed into the exterior trim. The sashes and screen slide in tracks and can be raised and lowered to fit the season.

The type of frame material on a storm window unit is important because it contributes to the storm window's heat conductivity and maintenance. Wood, aluminum, or vinyl are the most often used window frame materials.

Most storm windows have aluminum frames and tracks, although wood and vinyl frames are more resistant to heat transfer. There are some disadvantages to wood frames. Wood weathers with age and expands and contracts according to weather conditions. Wood-frame storms installed during the winter may not close easily during the summer, and those installed during the summer may fit loosely in the winter.

A wood frame also requires three times more material than a metal frame. This results in less glazing, and consequently, less solar heat gain and view. Wood frames also require the most maintenance.

Vinyl frames are usually made of polyvinyl chloride with ultraviolet light (UV) stabilizers to keep the material from breaking down. Vinyl frames are a better insulator than aluminum, but may be difficult to locate. Vinyl frames may expand and warp at high temperatures. In hot climates, colors other than white will fade. To have the best of both worlds, you can choose an aluminum or vinyl-clad wooden frame.

-- Tips courtesy of HomeAdvisor.com