Uf = heat transfer coefficient for the window frame (f for frame). In order to assess the quality of a window in terms of its thermal insulation, the insulation value of the frame-sash combination, which is described by the so-called Uf value, is crucial. The often published total value of a window Uw , on the other hand, is very strongly influenced by the selected glass pane, so that it does not make a direct statement about the frame quality.
The information listed in the table on bauwion page 312 | Wooden windows and wood-aluminium windows apply to the coniferous woods fir, pine and spruce. Due to the higher bulk density, increased Uf values must be taken into account for other types of wood, e.g. meranti and larch + 0.1 W/ m²K, oak + 0.2 W/ m²K.
Unit of measurement: W/ m²K
Source: bauwion
