NFRC - Winter Insulating Performance

Keeping your home comfortable and energy efficient with windows


pdf For a printable version of the NFRC Window Performance Sheet, Click Here

winter insulating performance
summer solar control
Sound Control
UV Protection window
Insulation performance is measured to determine how effectively a window keeps heat in a home. Better insulation in windows means lower energy costs, and just as important: improved comfort on cold winter days. Insulation performance is measured in U-values. The U-value is a measure of heat loss through a window; therefore a lower U-value means better insulation performance. In the past, windows typically had U-values of around .48. Gilkey System 10 Windows (with R 10 glass) are truly energy efficient, offering glass that is 50% better at keeping winter heat in your home compared to Low-E with argon gas. This superior performance will make your home more energy efficient and comfortable. The chart below compares the insulating performance of different glazing products.

You should select a window with lower U-values if:
  • Reducing heating costs is a factor in your window investment.
  • Your home has large areas of glass.
  • Improving the insulating value of your windows may be necessary to comply with local energy codes.
  • You sit near your windows in the winter.
NFRC Winter Performance comparison