Glass Options Mean Energy Savings

Why an Energy Efficient Window?

If you are in the market for new windows or replacement windows, one factor to consider is the energy efficiency of the window. More states are starting to adopt Model Energy Codes, which means that if you are building a new structure or even buying replacement windows, the windows must meet certain energy efficient criteria. This is due to the fact that in 1990 alone, the US spent $20 billion on heating energy to offset unwanted heat losses or gains in commercial and residential buildings. This number represents one quarter of all the energy used for space heating and cooling. Most of this heat loss or gain occurs through windows and doors. A smart shopper should look for an energy efficient window and have it installed properly, as an improper installation will defeat the purpose of the window's energy efficient design. As a window becomes more energy efficient, the price of the window will be higher, but the higher price will be justified when you see the savings you obtain in your heating and cooling bills.

What Glass Options Make a Window Energy Efficient?

There are many ways to boost the thermal efficiency of a window though glass options. Most windows today use insulated glass units (IGUs), as these perform better than a single pane of glass. A single pane of glass has an insulating value of approximately R-1. The single pane window can account for considerable heat loss or gain in a home. The traditional approach to a more energy efficient window has been to add more panes of glass to the unit, because the multiple panes increase the ability of a window to resist heat transfer. These multiple pane IGUs can be improved upon by adding an inert gas such as Argon or Krypton to the airspace between the panes of glass. The inert gas improves the thermal efficiency of an IGU because the molecules of the inert gas are heavier than air molecules, and this means that it takes a longer time for heat to transfer through these molecules. Low-E glass is another option to consider for energy savings. Low emissivity glass is placed on the outside pane of the IGU and the Low-E coating will reduce heat loss in the winter, yet reflect the re-radiated long wave energy from macadam, or other similar objects in the summer, thus keeping the home cooler. To find out more about the Guardian Acclimate RLE Glass that Air-Chek Window Depot uses, visit Guardian's site at http://www.guardian.com.

Another factor to consider when looking at glass options is the amount of air-space between the panes of a double paned IGU. The U.S. Department of Energy's Energy Efficiency and Renewable Energy Network (EREN) has conducted tests on IGUs and found that the optimum air-space between glass panes should be between 1/2 inch and 5/8 inch for maximum insulating values. At Air-Chek / Window Depot, our double pane IGUs have 9/16 of an inch air-space.

Cut-Away Views of a double glazed and a triple glazed IGU

On the left is a standard Air-Chek 3/4" IGU with single strength clear glass and aluminum spacer. On the right is a triple glazed unit with Guardian Acclimate RLE low emissivity glass on the outside and inside panels, and clear single strength clear glass making the middle panes. The brown material inside the spacer is a molecular sieve which absorbs moisture from within the sealed unit. The gray material is hot melt butyl which is used to hermetically seal the IGU. The double pane unit is shown with 9/16 aluminum spacer and the triple unit is shown with warm edge thermo plastic spacer. The air space between the panes of glass can be filled with either Argon or Krypton gas to improve the thermal efficiency of the unit.

Independent Lab Test of Ultra Double Hung

Below is a chart showing the overall thermal performance of our Ultra Double Hung window. The first column lists the components of the IGU, and the 2nd and 3rd columns give the U-Value (1/R-value) of the overall product. These test results are from 1999.