Feb 13, 2013 5:00 PM  PST

GreenPointers: Windows

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GreenPointers: Windows

Our series of GreenPointers provides helpful tips for a healthier, greener home in a variety of topics. Today's topic is Windows.

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Windows give us a view out into the world, but that's not all they do. They also play a big role in how energy efficient and comfortable our homes are. During the warm months, older single-pane windows can allow unwanted heat into the home, and in the winter, they can account for as much as 25% of the home's heat loss.

Today's high performance double-pane windows reduce heating and cooling costs and keep homes more comfortable. If replacing single-pane windows with high performance windows isn't in your budget, consider lower-cost options such as applying solar control window film or installing storm windows.

Here are a few ways to make your windows more efficient.

Step 1


  Solar control window film can be applied to existing windows to reduce solar heat gain through the glass while still transmitting light and providing visibility. Look for products with a solar heat gain coefficient (SHGC) of 0.40 or lower, or shading coefficient (SC) of 0.44 or lower. The lower the SHGC or SC, the less heat the film will allow in.

Window film should only be used on single-pane windows. Consider using solar control film on all east- and west-facing single-pane windows to reduce heat gain into the home. Window films can be applied by a commercial installer; do-it-yourself products are also available at most home improvement stores.

Step 2


  Storm windows are temporary windows installed over the standard window to improve energy efficiency and comfort. Some storm windows are designed to be installed on the window's interior, while others are mounted on the exterior. Measure existing windows and order storm windows from a window supplier. Storm window panes are typically mounted in the winter to provide additional insulation and wind protection, and then removed in the spring.
Step 3


  These days, windows are available in a dizzying array of options. Today's high performance windows have many features that make them stand out over basic single-pane windows, including:
  • Multiple panes of glass, with an air- or gas-filled space between them, to provide better insulation
  • Improved frame materials to reduce heat transfer and insulate better
  • Special low-e coatings on the glass to keep heat inside in the winter and outside in the summer
  • Warm edge spacers between the panes of glass to reduce heat flow and prevent condensation
In addition to the energy savings you will receive, there are many other reasons to replace existing single-pane windows with high performance windows. Your old windows may have rotted frames or sashes, or you may want to cut down on noise from outside or reduce drafts inside. Or perhaps you simply want to bring more daylight into certain rooms.

When shopping for new windows, choose double-pane products with a U-factor of 0.40 or less. In addition to a low U-factor, the windows should have a solar heat gain coefficient (SHGC) that suits your climate and the window's orientation. Choose windows that use wood, fiberglass or vinyl frames which insulate much better than aluminum frames.

Visit www.efficientwindows.org for help in choosing the best criteria for windows in your climate and for your specific application. Check with your local utility company for rebate programs for high performance windows.


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