• Multiple Layers of Glazing: Each layer of additional glazing improves the efficiency of a window, as dead air between panes prevents conduction of heat. Proper spacing of panes prevents convection loops from occuring between the window panes, further reducing heat loss.
• Tinted Glazing: Tinted glass and tinted window films reduce the amount of the sun's heat entering the building. The shading coefficient (SC) of a window is the amount by which the window reduces heat gain. The lower the shading coefficient, the less solar heat is admitted. New glazings reduce the heat gained by your house without reducing visibility as much as older tinted glass and films. Visible light transmittance (VLT) is the measure of the amount of light that comes through the window. Select a window with a VLT of 0.60 or higher.
• Frame Material: Wood, vinyl or fiberglass frames conduct less heat than aluminum frames, increasing window efficiency.
• Thermal Break: A material that doesn't transmit heat well, such as plastic, sandwiched inside the metal parts of the frame. This reduces the heat being transferred through the frame. Thermal breaks can be used in the spacer between panes of glass in multi-pane windows as well as in the main body of the frame.
• Low-E Glazing: A special window coating that helps prevent the warmth inside your house from escaping through the glass in the winter (pyrolitic). A variation (solar control) is designed to block heat from the summer sun. Low-E coating can reduce energy use by up to 35 percent.
• Gas Fill: An inert gas such as argon is used instead of air between the window panes. Inert gases have a much better insulation value than air.
• Condensation: Condensation is the buildup of water droplets on a cold window pane. This can occur on the inside of single pane windows, and in between the panes of multiple pane windows. Condensation on single pane windows can damage windowsill and wall surfaces if extensive. Condensation between the panes of multiple pane windows indicates a problem with the seal between the panes.
• U-Value: U-Value is a measurement of heat flow. The lower the U-value, the more slowly the window transfers heat in and out of your home.
• R-Value: R-value is a measurement of heat resistance. It is the inverse of the U-value, so the higher the R-value the better the window resists heat transfer.

For more windows terminology, visit the Efficient Windows website.

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