How Do Double Pane Windows Insulate?
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Windows and Panes
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With the price to heat and cool an average home going through the roof, saving energy has become a high priority for many homeowners. After you've insulated your attic and walls, it's time to turn your attention to your windows. According to Paul Fisette, writing for the Building and Construction Technology department of the University of Massachusetts, Amherst, "Most (windows) are 10 times less efficient than the wall area they replace. An average home may lose 30 percent of its heat or air conditioning through its windows."
Insulating Windows
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An average single pane window will have an R-value (a measure of heat flow resistance) close to zero. A single pane of glass will keep the wind from blowing through the house but provides almost no protection from conductive heat loss.
Double-glazing is the practice of putting two panes of glass separated by dead air space in the window frame of 1/4 to 1/2 inch. The air between the panes of glass slows the transfer of heat and can double the insulating properties of the window.
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Improved Insulation
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The insulating properties of a double glazed window can be improved by filling the space between the panes with a less conductive inert gas like argon. Argon is a safe, nontoxic gas that is part of the air we breathe every day. Being less dense than air, argon transfers heat more slowly.
Low-emissivity glass is treated with a clear, heat-reflective coating that further decreases loss by blocking the transfer of heat in the form of infrared radiation.
Double and even triple glazing in combination with argon gas and low-emissivity coatings can block heat loss or gain and trim a significant portion off your energy bill.
More Than Panes
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Insulating the glass will greatly reduce heat lost through window openings. Glass covers only a portion of the window opening. Heat loss through the frames can be significant as well. Aluminum window frames can transfer heat quickly. Vinyl is not quite as conductive. Wood, while expensive, is the best natural insulator commonly used for window frames.
Many window manufacturers now make aluminum and vinyl windows with "heat breaks," or strips of insulation built into the frame. Sandwiching an insulating material into the frame during construction can bring the R-value of the window up considerably. The higher the R-value, the more efficient the window becomes.
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