U-Value or U-Factor in Replacement Windows

U-Value (U-Factor)

When replacing your windows, you will likely run into a number of different

The U-value, also called the U-factor, is a measurement of non-solar heat transfer through a window. The amount of heat gained or lost through a window can significantly influence heating and cooling costs in the home, especially in colder climates. A lower U-value indicates lower heat transfer and better insulation properties. A U-value of 0.3 is considered good, although some high-efficiency windows now surpass that.

The U-value is measured by determining the difference between the temperature inside and outside the window. This measurement generally applies to the entire window, including the glass, frame, and spacer. A second measurement, called the center-of-glass U-factor measures only the heat transfer of the glass itself, but this measurement is used infrequently.

Low-emittance coatings, argon or krypton gas fills, and spacers with low thermal transfer can all contribute to a lower U-value.