Energy Efficient Replacement Windows

The most important factor in determining whether to purchase a window is its energy efficiency.  To define energy efficiency in a window, there are two very important variables to look for in the glass: the Solar Heat Gain Coefficient (SHGC) and the U-Factor.  Every glass manufacturer should have this information available to the public, and you should not purchase a window if those values are not provided.

What is Solar Heat Gain Coefficient?

Solar Heat Gain Coefficient (SHGC) is a ratio that defines the amount of solar radiation that goes through a glass.  The lower the SGHC number is the better.  The values range from around 0.2 to 0.8 and anything lower than 0.4 is considered very good.  If you want to block solar radiation heat from your house during a hot summer, then purchase windows with low SHGC values.

SHGC is sometimes confused with shading coefficient (SH).  If you are given the shading coefficient number of a window, multiply it by 0.87 to get the SHGC number.

Definition of U-Factor

The U-factor of a glass defines the rate at which heat passes through the glass.  Like the SHGC, the lower the value the better.  Windows with low U-factors will offer great insulation to a house or building during a cold winter.  Double-pane windows are a necessity for cold winters since they are much better at insulating than single-pane windows.  U-factor values range from about 0.4 to 1.2, so make sure and get a window with a value of 0.6 or less if you live in a cold city.

Replacement Windows

If you’re thinking of replacing the existing windows in your home, here are some rule of thumbs to follow:

  • Use the Energy Star website to find stores in your area that sell Energy Star qualified windows.
  • The National Fenestration Rating Council (NFRC) has a comprehensive database of windows and window manufacturers in the US so you can search for exactly the type of window you want.
  • Quality vinyl frame windows are better at insulating the house than traditional aluminum frame windows.
  • Always check the manufacturer’s label that shows how energy efficient the window is.  The label should at least have the SHGC and the U-Factor values.
  • After installing the windows, make sure and seal the window sills with insulating caulk as they are usually the first place where air infiltration will enter a room.
  • If you live in a city with cold winters, always get double pane windows
  • Windows come with different shades, but the SHGC is the most important factor in blocking out solar heat from a house.

The video below shows a step-by-step process on installing replacement windows.

When replacing windows in your home, think of style and home decoration, but also think of saving energy and comfort.  Carefully selected and installed windows can significantly reduce heat loss in the winter and prevent heat gain in the summer while lowering your utility bills.

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