u-value, definition of

U-value applies the factor of time to the heat-loss measurement. U-values measure heat that escapes per hour through a window. Windows typically have two U-values: one for the glass and one for the window, including the frame.

• What is R-Value, U-Value and how do they relate to insulation?
  How the R-value of a buildings insulation or home is calculated and the factors that effect the final R value, and how to use it.

• R-value to U-value Calculator
  R-value to U-value conversion calculator