Energy Efficient Windows...Continued

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-value = 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: (1) are based on current standards set by the American Society of Heating, Refrigeration, and Air- Conditioning Engineers (ASHRAE), (2) are calculated for the entire 3. Traditionally, clear glass has been the primary material available for window panes in homes. Window, including the frame, and not just for the center of the glass, and (3) represent the same size and style of window.

The following five factors affect the
R-value of a window.

     • The type of glazing material (e.g.,
        glass, plastic, treated glass)
     • The number of layers of glass
     • The size of the air space between the
        layers of glass
     • The thermal resistance or conductance
        of the frame and spacer materials
     • The "tightness" of the installation.

New technologies and advancements in today's window marketplace make upgrading a necessary and cost effective way to both beautify your home, as well as ease energy costs both in the summer and the winter.