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Glass Panes
Windows, Skylights & Doors


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
 
 

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