Window Performance Criteria for Energy Star Certification

Not all replacement windows are the same—the Energy Star seal sets the best replacement windows apart. There are certain standards that an energy-efficient replacement window must meet to earn this seal, which indicates that it is among the best on the market for providing quality performance. Two of the most important are U-factor and the solar heat gain coefficient.

  • U-Factor: One of the most important measurements of an energy-efficient replacement window is its U-factor. This measurement determines how well a replacement window insulates against heat transfer. The lower this number, the better the window insulates against thermal change. For Energy Star qualifications in the Northern region, homeowners should seek a U-factor of 0.32 or lower.
  • Solar Heat Gain Coefficient: The second most important measurement, SHGC is a performance measurement that determines how well a window blocks heat from the sun. As with U-factor, the lower the number, the more insulated the window. An SHGC around 0.35 is a good starting point.
  • Double Panes and Gas Fills: Single-paned windows quickly transfer heat from one side of the window to another, making them woefully inefficient. Double panes with gas trapped between the glass resist this heat transfer and improve the energy efficiency of the window. Gas fills are ideal, because they insulate far better than air alone.
  • Low-E Glass: Special low-emissivity coatings are typically applied to the inside windowpane. These coatings resist the transfer of heat from inside the home and help to prevent ultraviolet light from penetrating a room.
  • Warm Edge Spacers: Often nested inside the frame itself, these spacers are designed to keep the panes of glass a uniform distance apart no matter what the temperature inside or outside the home. This increases the effectiveness of gas fills.

Wallside Windows’ replacement windows proudly bear the Energy Star seal. Learn more about our factory and our products when you visit our website, or give us a call at (313) 908-5243 with any questions.