One popular notion is that replacing your current windows is the only way to cut energy loss and save money.
So, it would seem that there can be no better way to improve cracked window glass, foggy glass, air infiltration around the edges, and dated window sashes than to replace them with newer and better ones. Even lower-cost windows, with low-e coating and double-glazing, can be so technologically advanced that they far exceed the performance of old windows.
But sometimes replacing windows is not a viable option. Installing new windows all throughout a house is an incredibly expensive proposition. Plus, claims that some window companies may advance, that the new windows will pay for themselves with energy savings, may not be true for all. It may take many years to recoup the cost of whole-house replacement windows with attendant energy savings.
While it is true that replacement windows are, in many cases, the best way to slow energy loss, there are retrofit alternatives that cost less and offer nearly the same performance as new windows. So, for many homeowners, retrofit window modifications are the easiest and cheapest solution.
What Retrofit Windows Are
Retrofit windows are modifications to existing windows that improve the windows' energy-saving capabilities. Retrofit window solutions can include modifications such as storm windows, interior window panels, and interior thermal blinds.
A report by The National Trust For Historic Preservation finds that "retrofit strategies come very close to the energy performance of high-performance replacement windows at a fraction of the cost."
This means that three retrofit window methods will save nearly the same amount of energy as entirely replacing the windows. Factoring in retrofit windows' low cost in relation to replacement windows' high cost, the scales begin to tip in the direction of window retrofitting.
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Exterior Storm Windows
Homeowners often install exterior storm windows with an eye toward saving energy and money, yet they find that their efforts count for little.
The problem is not so much the storm windows as the approach to purchasing and installing the storm windows.
Some homeowners may purchase poor-quality storm windows that permit air leakage. Or they may install them with little care. More than anything, relying on storm windows alone to fix bad windows is never a solution. Storm windows are a supplement to a home's windows but they will never approach the weathertight nature of true windows.
Complicating matters is the fact that many homeowners lack the skills or inclination to install storm windows where they are most needed: the upper floors.
The highest value storm window is a low-e single-clear operable exterior storm; aluminum triple-track frame. While better quality storm windows are available, this window provides the best value, when the cost is factored in.
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Interior Window Panels (Inside Storm Windows)
Interior storm windows, sometimes called invisible storm windows, are installed parallel to your existing window and improve the thermal and air leakage performance of the window.
Interior storm windows are similar to shrink-fit window film insulation that attaches to window trim with double-sided tape. The difference, though, is that window film is flexible and temporary, while interior storm windows are solid acrylic and semi-permanent.
Interior storm windows attach via magnetic strips or compression gaskets and can remain in place for as long as the homeowner desires. By contrast, shrink-fit window film only lasts one season, if that.
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Cellular Blinds (Interior Insulating Blinds)
Interior cellular blinds are made of lightweight fabric and open and close in an accordion fashion. When the blind is fully extended, a honeycomb-like structure forms a thermal shield between the cold window and the warm interior.
Some cellular blinds install at the top of the window frame, much like mini-blinds. Better cellular blinds run along weather-stripped edge tracks to keep the blinds in place and the cold out.
Equally effective are quilted window blinds. These are made of thick, quilted fabric that rolls up and down.
One obvious downside of using thermal blinds as your retrofit window solution is that they are not transparent. They can only be used at night or, if you wish, during the day (thus not allowing natural light into the house).
Yet as nights lengthen and days shorten throughout the winter, there are far more opportunities to pull down the blinds and push back the cold.
10 Things You Should Know About Retrofitting Historic Windows / The National Trust For Historic Preservation
Saving Windows, Saving Money: Evaluating the Energy Performance of Window Retrofit and Replacement. National Trust for Historic Preservation.