While modern folk think of storm windows mostly in terms of energy efficiency, the old-timers developed them as additional protection against damage from tropical storms, nor'easters and other harsh weather. Much is made of the fuel-saving benefits of storm windows during winter, but they also reduce cooling costs in summer. If you have important decisions to make regarding storm windows -- or windows in general -- understanding how they work and how they've evolved in recent decades can save you a lot of money and headaches.
Two Panes Are Better Than One
Storm windows work by first acting as a barrier to air loss, and well-fitting storm windows almost eliminate it. In winter, they reduce drafts by preventing cold air from entering, saving fuel and making the house more comfortable. When they hold back summertime heat infiltration -- or cool air loss -- your air conditioner's cooling load goes down. This not only reduces cooling costs and makes the house more comfortable for your family, it can also prolong the life of the air conditioner by preventing it from becoming overtaxed.
Once you tighten your house with storm windows, you get another big benefit. The dead air space between the storm and the sash acts as a barrier to heat transfer. Without this natural insulator, heat would easily pass through the window to the outside in winter. In summer, the heat would transfer inside, making your cooling unit work more. As a bonus, because the panes are warmer in winter, you'll see less condensation of water vapor from cooking, showering and the like.
High Tech Boosters
Recent decades have brought big changes to storm windows that increase their energy efficiency. Once available only on full, double-glazed units, a low-emissivity -- low-e -- coating acts as an infrared barrier that slows down heat transfer through the glass. Useful in winter because they reduce heat loss, low-e coatings also reduce heat gain in summer by blocking infrared energy -- heat -- from the sun and outside air. Shade from trees and awnings advance the summer energy benefit of your high-tech storms even more.
Modern storms with all the bells and whistles give homeowners many options. Outright replacement with double-glazing was once the standard practice when dealing with old, drafty windows. Homeowners can now get the benefits of modern window technology without the full expense of demolition and replacement. This can also be helpful if you like your charming old windows or the local historic preservation board requires that you keep them.