In windows there are always three different U-values:
- Uw (w = window) – overall value of the window
- Ug (g = glazing) - U-value of the glazing
- Uf (f = frame) – U-value of the frame
The heat transfer coefficient Uw relates to the entire window. This value also incorporates the U-values for the glazing and the frame Uf. The overall value Uw is also influenced by the linear heat transfer coefficient (g = glazing) and the size of the window.