A window has several components: the frame, the sash and the glazing. The frame is the structure that surrounds the perimeter of the window. It's typically made of wood, aluminum or vinyl. The sash is usually made of the same material as the frame. It surrounds the glass. The glazing is the glass. A window with a single pane of glass is called a single-glazed window. A double-glazed window has two panes of glass separated by a narrow space filled with argon or krypton gas. Double-glazed windows are often referred to as double-insulated, or thermopane, windows.
Single-Glazed Vs. Double-Glazed
Single-glazed windows insulate against the outdoors by blocking the exchange of heat. They also generate some heat through the greenhouse effect, in which sunlight that strikes the glass surface is converted to heat waves. Double-glazed windows function in the same way as single-glazed. However, their insulating power is increased by the cushion of gas that fills the space between the panes because this layer further blocks heat exchange.
Double-Glazed Vs. Thermopane
Thermopane was a brand name of double-glazed insulated windows. According to DwellGreen, C.D. Haven invented Thermopane insulated glass in the 1930s. A German company, Behr GmbH & Co. KG, owns the Thermopane trademark as of early 2012, according to the U.S. Patent and Trademark Office. Although Behr GmbH & Co. KG manufactures glass, there's no evidence that the company manufactures or markets a Thermopane brand. Thus, there’s no difference between a double-insulated window and a "thermopane" window. The term thermopane is used generically, albeit inappropriately, to refer to a double-insulated window.
Low-emissivity, or Low-E, is a feature of modern double-glazed windows. The term refers to a metal oxide layer applied to the exterior face of the interior glazing. This layer provides additional protection against heat loss while allowing sunlight through. A Low-E double-glazed window offers about the same degree of insulation as a triple-glazed window. A triple-glazed window has three panes of glass separated by two gas-filled spaces.
The primary benefit of double-glazed windows is that they're more energy efficient than single-glazed windows. However, different double-glazed windows provide different degrees of efficiency. Ratings help consumers make smart purchase decisions. The U-Factor measures heat transmission from the difference between interior and exterior temperatures. Lower numbers are better. The Solar Heat Gain Coefficient represents the speed with which solar heat passes through the window. These and other ratings can be found on a window's National Fenestration Rating Council label that serves as an independent consumer guide to energy efficiency.
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