Consumption and Conservation

What changes have been made to make windows more efficient?

Windows can account for 10 percent to 25 percent of a residential heating bill. During the winter months in cold climates, there may be significant heat loss through the windows. Conversely, during the summer and in warm climates, air conditioners must work harder to cool hot air from sunny windows. Until recently, clear glass was the primary glazing material used in windows. Although glass is durable and allows a high percentage of sunlight to enter buildings, it has very little resistance to heat flow.

Glazing technology has changed greatly during the past two decades. There are now several types of advanced glazing systems available to help control heat loss or gain. The advanced glazings include double- and triple-pane windows with such coatings as low-emissivity (low-e), spectrally selective, heat-absorbing (tinted), reflective, or a combination of these; windows can also be filled with a gas (typically xenon, argon, or krypton) that helps in insulation.


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