Glass and the energy efficiency of windows and glazed doors
When buying a window, a skylight or a glazed door, the type of
glass used in them is crucial.
Frames
and sashes are important, the gas between the glass panes
is important, the thermal breaks are important in aluminum
windows, but the type of glass is crucial…
According to US DOE EERE
over 25% of the heating and cooling energy bills in a typical
home
are due to bad inefficient windows, door and skylights, and
namely to the type of glass used. Glass is a crucial element in
the home energy efficiency battle. Clear single glass is highly
inefficient and causes too much energy to be lost, and too much
sunlight to enter in homes when unwanted.
Low-E
coating glass and Low
E2 glass (also called solar low-E, or spectrally selective glass)
are the most common types of glass for boosting the
energy efficiency of windows, glazed doors and skylights.
Note:
The energy efficiency of a glass pane is mainly measured by the
U-factor and the SGCS coefficient, which are contemplated in
rating labels as those of Energy Star. For more information on
them, see: Rating of windows, doors
and skylights
Cold and
temperate climate glass
In cold and temperate climates you should look for windows, doors, and
skylights with a low emissivity glass, capable of limiting as
much as possible energy losses...
To obtain that,
the low-E double (or triple) pane,
used in
conjunction with gases (argon, krypton, carbon dioxide...)
filling the spaces between panes,
is the ideal;
low-E (low-emissivity) coating highly reduces heat loss
through the windows, skylights and glazed doors.
Hot
climates glass
In hot climates, where cooling costs are higher than heating costs, you should look for windows, doors, and
skylights with a low SHGC (Solar Heat Gain Coefficient): 0.4 or
less...
To obtain that, solar control
glass (also called Low E2 and spectrally selective glass) is the
best option. This glass is a good insulator and is the best on
limiting solar heat gains due to its capacity of blocking infrared and some
ultraviolet rays...
Besides, its high capacity to
reduce solar heat gains allows more glass area to be added
without increasing cooling costs.
Impact resistant glasses and tinted glasses
Besides e-low glass and Low E2 glasses, there
are also impact-resistant glasses (to improve the safety in
areas prone to flying debris or high winds), tinted glasses (to
improve privacy or control solar heat gains…) and hydrophilic
glass exterior coatings to reduce the frequency of cleaning.
Low E2 glass or
darker tinted glazings?
In hot or even in temperate climates, we can
put the alternative: should we use darker tinted glazing or Low
E2 glass?
Darker tinted glazing is a good option to provide lower solar
heat gains, but it isn't as efficient as Low E2 glass and yield
a decreased outdoor visibility, particularly at night.
See also:
Windows, Doors and Skylights basics
Frames and sashes
Advanced Doors
Skylights
Weatherstripping
Caulking
Rebates and Tax Credits
Back to top Advanced Energy Efficient Skylights
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