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Bob Crager
Bob Crager of Lewis Street Glass is a 26 year veteran in the glass business. Lewis Street Glass is a leading Wichita Glass company, serving the entire Wichita/Sedgwick County area since 1919. They do anything and everything having to do with glass, both residential and commercial. They also do Auto glass. They are located at 743 South Market, facing Kellogg on the South, and you can reach them by phone at (316) 263-8259. You can email Bob Crager at bcrager@lewisstreetglass.com
Glass
2004-10-01 15:07:00
Reducing heat loss
: We have been saving to purchase new windows for our home. What are some things to look for to be the most energy efficient?
ANSWER: Manufacturers usually represent the energy efficiency of windows in terms of their u-values (conductance of heat) or their r-values (resistance to heat flow). If a window's r-value is high, it will lose less heat than one with a lower r-value. Conversely, if a window's u-value is low, it will lose less heat than one with a higher u-value. In other words, u-values are the reciprocals of r-values (u-values = 1/r-value). Most window manufacturers use r-values in rating their windows.Usually, window r-values range from 0.9 to 3.0 (u-values range from 1.1 to 0.3), but some highly energy-efficient exceptions also exist. When comparing different windows, you should ensure that all u- or r-values listed by manufacturers: • Are based on current standards set by the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE), • Are calculated for the entire window, including the frame, and not just for the center of the glass, and • Represent the same size and style of window. The following five factors affect the R-value of a window.1. The type of glazing material (e.g., glass, plastic, treated glass) 2. The number of layers of glass 3. The size of the air space between the layers of glass 4. The thermal resistance or conductance of the frame and spacer materials 5. The "tightness" of the installation (i.e., air leaks (see last month's column). Traditionally, clear glass has been the primary material available for window panes in homes. However, in recent years, the market for glazing, or cutting and fitting window panes into frames, has changed significantly. Now several types of special glasses are available that can help control heat loss and condensation.Low emissivity (low-e) glass has a special surface coating to reduce heat transfer back through the window. These coatings reflect from 40% to 70% of the heat that is normally transmitted through clear glass, while allowing the full amount of light to pass through.Heat-absorbing glass contains special tints that allow it to absorb as much as 45% of the incoming solar energy, reducing heat gain. Some of the absorbed heat, however, passes through the window by conduction and re-radiation.Reflective glass has been coated with a reflective film and is useful in controlling solar heat gain during the summer. It also reduces the passage of light all year long, and, like heat-absorbing glass, it reduces solar transmittance. Storm windows can increase the efficiency of single-pane windows, the least energy-efficient type of glazing. More Next Month…
 
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