U-VALUE WINDOW / Calculation

  • There are basically three U-values for windows:

    • U w (w = window) total window value
    • U g (g = glazing) U-value of glass
    • U f (f = frame) U-value of the frame
    • The heat transfer coefficient U w applies to the entire window. This value includes U-values for glazing U g and frame U f. The total value of U w also affects the linear heat transfer coefficient g (g = glazing) and the size of the window.

    Learn more about the different U-values of the Deceuninck window system


  • U g

    Typical U-values for glass panel insulation are:

    • Double insulating glass 24 mm with argon filling: 1.1 W / m2 K
    • Triple insulating glass 36 mm with argon filling: 0.7 W / m2 K
    • Triple insulating glass 44 mm with argon filling: 0.6 W / m2 K
    • Triple insulating glass 36 mm with krypton filling: 0.5 W / m2 K


  • The value of the profile display width is taken in f w.


  • The value of ψg glazing of the edge joints is mainly influenced by the insulating glass gap material. Aluminum is used as the standard material with the worst thermal. Thermally enhanced spacers are called “thermal edges”. The spacers are made of stainless steel or plastic, which further improves the value of the angle seal by increasing the level of the insulating glass profile.

    Examples of -W values:

    • Aluminum spacing: approx. 0.08 W / mK
    • Thermal edge spacing: approx. 0.04 W / mK


  • The heat transfer coefficient for windows and doors U w is usually calculated in a standard window size, 1.23 mx 1.48 m.


    At smaller dimensions, the U-value deteriorates and larger windows achieve better values. This is because with glazing, better U-values are possible compared to the frame material and so the thermal value can be achieved with larger glass surfaces.

    According to EnEV 2009, the value of U w must not exceed 1.3 W / m 2 K in normal glazing. Windows with a U value of 0.8 W / m 2 K are used as a passive laboratory standard.

    U-w value calculation:

    The following formula is used to determine the heat transfer coefficients:

    U g = glazing heat transfer coefficient
    Uf = frame heat transfer coefficient
    psg = linear heat transfer coefficient of insulating glass seal
    A g = glass surface
    A f = framed area
    A w = A g + A f
    l g = circumference of the inner edge of the frame profile
    (or the visible circumference of the glass plate)

    Learn more about the different U-values of Deceuninck window systems.