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Home Energy: Shedding some light on windows

Question: We're working with a homebuilder in a large retirement community in Florida, and I see that one of our options is to choose either clear insulated window glass or tinted insulated glass. Any recommendations on our best choice?

Answer: There's been a fair amount of research on window options in recent years, so I can give you some thoughts on the choices you've got available.

Generally, if you have windows that face north, or windows facing any other direction that are well-shaded, the clear insulated glass can work well. If the east-, west- or south-facing windows are not properly shaded, though, you're going to get some serious glare and overheating problems, especially in a hot climate.

In considering your other choice, note that the phrase "tinted windows" can mean a lot of different things, depending on such factors as what they really are and where the tint is put. If the tint is in the glass of the outer pane, for example, then the heat it absorbs will be conducted or radiated back to the outdoors. Some of the sun's heat can also flow across air space in the glass to the inner pane, which is clear, so that pane will become warmer. Windows are available that have coatings on the inner surfaces of the glass that will reduce some of the radiant heat transfer from the hot pane into the home.

I asked Ross McCluney, a nationally known windows expert what he suggested for you, and he recommends double-pane insulated glass and frames in hot climates to improve overall performance in both winter and summer and help reduce peak electric usage. Your best choice is to put these better windows into the home now and start enjoying their benefits rather than waiting until you need to replace the windows in the future.

As for the window tints, he notes that there are big differences between types of tinted glass — made by putting dyes or other chemicals into the glass or a coating on the glass when it is made — as opposed to window films that you can apply in your home. If you already have clear windows in your home and can't afford replacement windows now and don't have good exterior shades, tint on your windows will give you some extra protection from the sun. Getting the right windows when the home is being built is the right way to enjoy maximum savings and comfort, however.

Consumers can verify the expected performance of different types of windows by reading the numbers from the National Fenestration Rating Council energy performance label that comes with windows. In your situation, note that a high Light-to-Solar Gain ratio (greater than 1.0 and hopefully closer to 1.5) — a figure obtained by dividing the visible transmittance (VT) by the window's solar heat gain coefficient (SHGC) — can assure you that you're getting a glazing system more suited for a hot climate, rather than one that will allow maximum solar radiant heat and trap it inside for cold weather comfort.

Visit the council's Web site for information on energy performance labels on windows and how you can use the information to choose the best window for your climate. These energy performance ratings will help you compare windows on such measures as how well they prevent heat from escaping, how well they block heat caused by sunlight, how much light they let into the house, how much air leakage there will be, how well they resist condensation, and other factors.

You can get a great deal of information on windows at the Florida Solar Energy Center that can help you choose the specific questions you need to ask your builder. Windows that keep a home comfortable and energy-efficient in one part of the country may be the worst choice for a home in a different climate.

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