Save Money with Energy-efficient Windows
January/February 2006
Steve Maxwell
 |
PELLA WINDOW CORP.
|
It pays to install better windows in your home. According to the
U.S. Department of Energy, installing energy-efficient windows can
reduce your heating and cooling bills by up to 25 percent.
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There are three main factors that affect a window's energy
efficiency:
- The first is heat flow through the glass and frame, which is
generated by the temperature difference between the inside of your
home and the outside environment.SOLUTION: Double- or
triple-pane windows are the best way to increase R-values (the
resistance to heat flow) because they increase the number of
barriers between the outdoors and the interior of your home.
Microscopically thin layers of clear metal oxides applied to the
glass during production, called 'low-emissivity' or 'low-e'
coatings, further help to reduce radiant heat transfer between
panes of glass by reflecting some or all of the infrared radiation
and heat flow exchanged between window panes.
- The second major factor is solar heat gain, also referred to as
the solar heat gain coefficient (SHGC). The SHGC measures how much
of the sun's energy (both visible and near-infrared light) striking
the window transmits as heat into the room.SOLUTION: In cold
Northern climates, you will want high solar heat gain to capture as
much of that passive solar energy as you can; an SHGC of 0.55 and
higher is recommended for this region. In hotter Southern climates,
however, a lower SHGC of 0.4 or less is suggested to keep the solar
energy out. In climates where heating and cooling are equally
important, an SHGC between 0.4 and 0.55 is best.
- The third factor that affects a window's energy efficiency is
air leakage. This is the air that flows through cracks between the
sash and the frame, or at the point where the window connects to
the wall.SOLUTION: The lower the leakage value, the better;
look for windows with air-leakage rates of less than 0.3 cfm/foot
(squared).
Read more about these high-performance, energy-efficient windows in
the December/January 2005 issue of
Mother Earth News.