Green your life at home, work & play

Interested in windows? September 7, 2010

The three purposes of a window in a temperate area are for ventilation, sunlight, and viewing.  The average cost per window for a replacement is between $300 and $700.  To replace all windows in a one-story, three-bedroom home with 10 windows can range from $3,000 to $10,000 depending on the cost per window.  To replace more windows in a two-story home with more windows can cost between $10,000 and $20,000. Find out how windows are rated to find out what suits you best.

Windows are rated by their U-factor and Solar heat gain coefficient (SHGC). A window’s U-factor is the rate at which it conducts non-solar heat flow, or how well a window prevents heat from escaping. This is measured in Btu/hr-ft2-ºF.  The lower the U-factor, the greater the insulation and more energy-efficient the window.  The SHGC is the fraction of solar radiation admitted through the window by being directly transmitted or absorbed, then released into the home as heat.  The lower the SHGC, the more efficient because of its less solar heat transmitted and greater shading ability.  A window with a high SHGC rating is collects solar heat gain during the winter effectively, and a low rating reduces cooling loads during the summer by blocking heat from the sun effectively.  The SHGC rating desired depends on the factors such as climate, orientation, and surrounding shading.

Visible Transmittance is also a measurable way to determine a good and bad window.  This measures the amount of light that comes through a window. The higher the VT, the more light is transmitted. This would be more desirable on the north side of a home for more passive solar heating, but not on the east or west sides.  Air Leakage is another rating that measures the air infiltration around a window, expressed in cfm/sq ft. The lower the air leakage, the better.

Windows are rated by the National Fenestration Rating Council (NFRC), who also certifies and labels doors and skylights. This label provides a reliable way to determine window’s energy properties to compare products easily for your interests. Some windows are more energy efficient than other, such as double-pane, low-e and argon filled windows. Look for the Energy Star designation as a starting point, as well as the NFRC label to compare between windows. You may also qualify for a tax credit, so check first before making a purchase. Finally, use a window selection tool such as this one to determine which window is best for your geographic area and needs.


One Response to “Interested in windows?”

  1. Theresa Says:

    This was very helpful! Window shopping can be very confusing, but now I know a little bit more about what I should look for.

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