Energy Efficient Windows

Overview

If you're replacing your windows to upgrade your home's energy efficiency, you should consider a complete home energy audit and retrofit at the same time. New windows are expensive and unless you have a tightly sealed and well-insulated house, you may not be getting your money's worth out of your investment.

Are Energy Efficient Windows Right for You?

The first thing that many people think about when trying to make their home more energy efficient is replacing their old, single-paned windows with new, double-paned, tripled-paned and/or low-E windows. While this will increase the efficiency and comfort of your home, it's also very expensive compared with other energy efficiency upgrades that will provide as much, if not more, benefit in terms of energy savings, utility bill savings and reduced carbon output. However, if you need to replace your windows anyway, you should definitely do it with high-efficiency windows and take advantage of tax credits for them.

If new windows are the right choice for you, there are a few things you should know before you buy, because different climates have different window needs. The efficiency of a window is determined by U-factors in cold climates and solar heat gain coefficients (SGHC) in warm climates.

Window U-Factor: In a cold climate, you should look for windows with a low U-factor. In order to be eligible for the 2010 federal tax credit, your windows must have a U-factor of 0.30 or lower. U-factors are made lower by the low-E coating on the windowpanes, which reduces the transference of heat from one side of the pane to the other. In other words, the low-E coating is going to help keep heat (expensive to produce) inside your home during the winter months. U-factors can be improved even more by purchasing panes filled with argon or krypton gas.

Window SGHC: If you live in a hot and sunny climate, you should look for windows with an SGHC rating or 0.30 or lower as well. This will qualify you for the tax credit and provide you with a window that is designed to keep solar radiation out of your home. Low-E coatings and gas filled panes also play a role in improving SGHC.

For mixed climates, your best bet is a window with low ratings for both the U-factor and the SGHC. While heat can be transferred easily through low-quality windowpanes, another problem area can be around the glass inside and outside of the frame where air leakage occurs. Air leakage problems can be solved with insulation, caulking and weather stripping, which is something an energy auditor can advise you on.

As we've mentioned above, new windows are expensive, so you'll want to combine this investment with insulation and air sealing for the rest of your house; this way, you'll enjoy the appearance of new windows with the energy savings benefits of reduced heat loss. For more information that will assist you in making smart decisions about this investment, contact an energy auditor who can help.

What Kind of Windows Do You Have?

There are a lot of new and different windows out there, but we'll make it easy for you in determining how energy efficient the different types are. Either they're really old and single pane (and hopefully you've got storm windows for them), they're kind of old and double pane, or they're new in the last 20 years, in which case, they're fine.

Single Pane: We're talking old school windows here. A single pane of glass, set in a wood frame. Nothing fancy. If you're unsure about whether you've got single or double pane windows, you can do a little trick. When it's dark outside, light a match and hold it up to the window pane. If you see a single reflection of the match, you've got single pane windows.

Single with Storm: If you've got single pane windows but you use storm windows in the winter, we've made this special category just for you. It may be a pain to install them each winter and take them out each summer, but it's worthwhile for your utility bills and your home's comfort if you can't afford the major upgrade to modern windows.

Double Pane: Double pane windows made before the 1980s fall into this category. Anything since 1990, even if it's a double pane window, we categorize as being "modern high efficiency." If you know your windows are old but you're not sure if they're single or double pane, you can do the match trick. When it's dark outside, light a match and hold it up to the window pane. If you see two reflections of the match in the glass, you've got double pane windows.

Modern High Efficiency: There are a lot of types of windows being made today and a lot of fancy terms being used to describe them: triple and quadruple pane windows, filled with argon or krypton, with low-e coatings. To make this easy, we're grouping all windows made since around 1990 into the category of modern high efficient. If your windows are less than 20 years old, this is your category.

There are certainly performance differences within this category from window to window that will have some impact, but it won't be much of a difference when compared to your overall home's energy efficiency. If you're not sure how old your windows are, the match test will come in handy again. When it's dark outside, light a match and hold it up to the window pane. If you see three reflections of the match in the glass (even if one of them is faint), you've got modern high efficiency windows. If you only see two reflections, then you've got double pane windows.

Don't worry if the seals on some of your windows are broken. It may be difficult to see through, but it doesn't affect the energy efficiency of your windows.

Last Updated: April 2010

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