Thinking About Energy Efficient Windows for Your Home?

To determine whether a window is energy efficient for your home, there are two variables that a person should look at.  The first variable is called the Solar Heat Gain Coefficient (SHGC) and the second variable is the U-Factor.  These two variables should always appear in the window’s manufacturer label to help a person decide before they purchase the window.

energy efficient windows and fan

This shows a good efficiency combo of new windows and a ceiling fan.

The SHGC determines how much heat in the form of solar radiation will pass through the window and into a home.  The SHGC is measured with a number that varies from about 0.2 to 0.8.  The lower the number, the better the window is at rejecting heat from the sun.  A clear glass clear usually has a SHGC of 0.8 and a shaded glass has SHGC numbers lower than 0.67.  Not necessarily the shading color, but the shading technology and window thickness will determine how low the SHGC of the glass can be.  There are windows with very dark shading that have higher SHGC’s than windows with lighter shadings.  SHGC is sometimes confused with shading coefficient (SH).  When given the shading coefficient, multiply it by 0.87 to get the SHGC.


The U-Factor in a window determines the insulation capacity of the window.  This means that during the winter, it keeps the heat in your house from going outside.  Just like the SHGC, the lower the U-factor value, the better. U-factor values range from about 0.4 to 1.2.  Single pane, 1/8 inch thick windows have a U-factor of 1.2.  Windows that are double pane and 1/4 inch have U-factor values of 0.7 or lower.  The value depends on the window frame, the thickness of the window, the type of glass, the gas inside a double pane window, and if there is any special coating on the window.  A very popular coating for lowering U-factors in windows is called low-e coating.  This coating is placed on the interior side of a window to help with the insulating effects of it by rejecting heat from a warm room back into the room.  Low-e windows are good at preventing heat from leaving a room while at the same time letting light pass through.

There is a large variety of types of windows to choose from.  So when deciding between styles, shape and color of a window, make sure and look at the SHGC and U-factor value as well. Selecting the correct type of windows will keep a house comfortable, nicely decorated and lower the heating and cooling bills.

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