Energy Efficient Windows

Windows bring light, warmth, and beauty into buildings and give a feeling of openness and space to living areas. They can also be major sources of heat loss in the winter and heat gain in the summer. In 1990 alone, the energy used to offset unwanted heat losses and gains through windows in residential and commercial buildings cost the United States $20 billion (one-fourth of all the energy used for space heating and cooling). However, when properly selected and installed, windows can help minimize a home's heating, cooling, and lighting costs. 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.