NFRC - Winter Insulating Performance

Keeping your home comfortable and energy efficient with windows

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

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.