How and Why to Choose Energy-Efficient Windows

Reader Contribution by Jennifer Tuohy and Home Depot
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Ever since I began researching sustainable living more than a decade ago, I have heard the same thing over and over again: The single most important step you can take to make your home “green” is to swap out your old windows with shiny, new, energy-efficient ones.

The U.S. Department of Energy estimates that the amount of energy lost annually through windows costs consumers $35 billion. Heat loss and heat gain through and around windows accounts for between 10 and 25 percent of our heating and air conditioning usage, the largest consumer of energy in a modern home.

According to Energy Star, energy-efficient windows can save 7 to 15 percent of this energy loss (with storm windows, that figure rises to 25 to 50 percent), saving between $27 and $111 a year on energy bills for a 2,000-square-foot single-story home with storm windows or double-pane windows, or $126 to $465 if your home has single-pane windows. That’s a significant saving both for your pocket and the planet.

If your home already has storm windows or double paned windows, you can take steps to further improve their efficiency by caulking and weatherstripping. Window treatments will also help keep heat inside in the winter and outside in the summer. However, if your windows are old, damaged and/or single-paned, there is no doubt that you will save a lot of energy by replacing them with Energy Star rated windows.


How Do I Choose an Energy-Efficient Window?

According to the American Council for an Energy-Efficient Economy the following are the key considerations to incorporate into your window buying decisions:

Warranties and Installation. Choose windows with good warranties, particularly against the loss of the air seal. Help mitigate any problems with this by making sure to have experienced contractors install your windows—and check to see if the installers can provide a warranty as well.

Energy Star Rated. Look for the Energy Star label, which includes requirements tailored for the four broad climate regions of the U.S. Additionally, to be Energy Star compliant, windows must have an NRFC label, which indicates the window’s performance ratings with regard to U-Value (how well the window prevents heat from escaping), SHGC level (how much solar energy is transmitted through the window), Visible Light Transmittance (measured on a scale between 0 and 1, the higher it is the more light can pass through), Air Leakage and Condensation Resistance. Here is an example of the NRFC label: 

Bigger is Better. Maximize energy performance by choosing windows with larger unbroken glazing areas instead of multi-pane windows, to reduce air leakage.

Choose Efficient Frame Materials. Based on your home’s age, look and location, different materials will work better for you than others. Here’s a look at the most popular options:

Wood: Still the most common material, it insulates well, but is not as durable as the other options and is significantly more expensive. If you go with wood, look for FSC certified wood.
• Aluminum:
This metal conducts heat, making it the least efficient option. However, it is impervious to moisture, insects and rot that plague wood. It will corrode when exposed to sea air, so it’s not a good choice for coastal climates.
• Vinyl (PVC):
Vinyl frames insulated with fiberglass are the most efficient choice, as vinyl insulates better than wood, and it is also about half the price. However, the manufacture of PVC produces toxins and the material itself is not biodegradable, but its longevity goes a long way toward countering that particular eco-concern.
• Fiberglass:
Fiberglass frames and wood-polymer composite frames are fast becoming a common option for high-efficiency windows. They insulate well, are stronger than vinyl and cheaper than wood. The frames can also be filled with foam insulation to enhance its thermal properties.

Opt for Extra Air-Tightness. ACEEE recommends considering air leakage specifications (listed on the NRFC label) carefully when selecting windows, but as a rule of thumb, opting for casement and awning windows over double-hung and other sliding windows will provide a stronger seal.

Get a Glaze. A Low-E coating, a transparent layer of silver or tin oxide, is becoming a standard option due to its ability to reduce the solar heat gain without reducing visibility as much as tinted glass. According to Energy Star, these coatings reflect infrared light, keeping heat inside in winter and outside in summer.

Layer Your Windows. Double-glazed windows insulate almost twice as well as single glazing does, and of course, triple glazing further increases the efficiency, and is an excellent way to reduce noise pollution.

Go Wide. Double-glazed windows rely on the air space between the panes of glass for increasing the energy-efficiency of the window. The wider the space, the less heat can be conducted through it, although it can’t be much wider than one inch or it loses efficacy.

Get Gas. Replacing the air between panes with a gas such as argon has also become a standard option in energy-efficient windows. The gas is denser and has a lower conductivity, reducing heat loss significantly.

Pick Proper Edge Spacers. The piece that holds the panes of glass apart, the edge spacer, provides the airtight seal for your window. Steer clear of aluminum spacers, which have a high conductivity, and instead opt for non-metal materials such as silicone foam or butyl rubber. ACEEE also advises to pay particular attention to warranties against seal failure.

Windows are literally holes in our walls that allow all that precious energy to leak out of our homes. Unless you are considering living in a windowless box, upgrading to energy-efficient windows still remains the greenest thing you can do for your home.

Photo credits Energy Star

Jennifer Tuohy provides advice on home energy efficiency for The Home Depot. Jennifer’s green home tips are designed to help homeowners improve the insulation effectiveness of their homes. To view Home Depot windows installation services available in your area, you can visit the company’s website. 

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