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Windows and Energy Efficiency


Windows can make or break the energy efficiency of a home. Heat gain and loss through the glass is responsible for 25%–30% of residential heating and cooling energy consumption, according to the U.S. Department of Energy.

When selecting windows for new construction or replacing a home’s existing windows, choose the most efficient options you can afford.

If that’s not an option for you, your windows could benefit from some simple fixes to increase the efficiency and comfort of your home.
Here are some suggestions from the DOE:
  • Check windows for air leaks. Then add caulk and weatherstripping to seal any leaks.
  • Add window treatments and coverings to further seal out the elements.
  • Add solar film to the interior side of windows.
  • Add shading on the exterior, such as awnings, outside blinds or overhangs.
  • If windows need to be replaced, there are many options to consider, and some are more energy efficient than others. The Efficient Windows Collaborative offers up tips for picking panes in Texas.
  • Make sure windows meet your local energy code, and look for the Energy Star label.
  • Look for energy-efficient properties on the National Fenestration Rating Council, or NFRC, label.
  • Compare annual energy costs for a typical house by using a computer simulation on the EWC website, efficientwindows.org.
  • Ensure proper installation for optimal performance and to avoid air and water leaks.
Here’s a guide to some of the window jargon you may come across.
  • U-factor: the rate of heat loss. The lower the U-factor, the better a window resists heat flow.
  • Solar heat gain coefficient: the fraction of incident solar radiation. A low SHGC means a window transmits less solar heat.
  • Visible transmittance: the amount of visible light transmitted. The higher the VT, the more light is transmitted.
  • Air leakage: The lower the AL, the less air will pass through cracks.
  • Condensation resistance: how well a window resists condensation inside. The higher the rating, the more resistant to condensation a window is.
Having an understanding of energy-efficient properties helps make choosing new windows easier.

The DOE recommends the following when selecting new windows based on the climate:
  • In colder climates, consider gas-filled windows with low-e coatings to reduce heat loss. In warmer climates, select windows with coatings to reduce heat gain.
  • Choose a low U-factor for better thermal resistance in colder climates.
  • Look for a low SHGC. Low SHGCs reduce heat gain in warm climates.
  • Select windows with both low U-factors and low SHGCs to maximize energy savings in temperate climates with both cold and hot seasons.
  • Look for whole-unit U-factors and SHGCs, rather than center-of-glass U-factors and SHGCs. Whole-unit numbers more accurately reflect the performance of the entire product.
The benefits of high-performance windows can go beyond heating and cooling savings.

High-quality windows can:
  • Improve visibility and the infiltration of daylight.
  • Enhance comfort by controlling drafts and reducing direct sunlight with proper coatings.
  • Reduce condensation with warm interior surfaces and insulating frames.
  • Reduce the fading of fabrics and furnishings by blocking ultraviolet radiation with coatings.
  • Reduce peak heating and cooling loads, which may allow for the downsizing of heating and cooling equipment or a reduction in overall energy costs.
  • Make the home quieter by preventing noise from penetrating.


Posted: 11/5/2020 2:44:31 PM
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