Windows · Thermal
Uwp calculator: a door or window with a panel
Uwp = (Ag·Ug + Ap·Up + Af·Uf + lg·ψg + lp·ψp) / A: each part's area times its U-value, plus the edges of the glass and the panel, over the whole size. A 1000 × 2100 mm door with a 100 mm frame, glass of Ug 1.1 above a 700 mm panel of Up 0.8, comes to 1.23 W/m²K; the same door all glass, 1.36 W/m²K.
The Uwp formula, EN ISO 10077-1
The worked example: the opening inside a 100 mm frame is 0.8 × 1.9 m. The panel takes 0.8 × 0.7 = 0.56 m², the glass 0.8 × 1.2 = 0.96 m², and the frame the rest of the 2.10 m², 0.58 m². The glass edge is 4.0 m long: (0.96 × 1.1 + 0.56 × 0.8 + 0.58 × 1.3 + 4.0 × 0.08) / 2.10 = 1.23 W/m²K.
A panel usually insulates better than double glazing and has no spacer, so it pulls the figure down twice: less glass area and a shorter glass edge.
What this page does not do
- It does not take a drawing. Glazing bars, transoms and side lights change the areas and the edge lengths; for those, add each light’s area and perimeter by hand or use the whole-window U-value page.
- It does not certify. A declared Uw or Ud for CE marking comes from the standard sizes and tested or calculated values; this is the same sum for your own size.
Questions people ask
- What is Uwp?
- The U-value of a window or door that has an opaque panel in place of part of the glass. It is worked out like Uw, with the panel's area times its U-value and the heat lost at the panel's edge added in (EN ISO 10077-1).
- How do you calculate the U-value of a door with a panel?
- Add each part's area times its U-value (glass, panel, frame), add the glass and panel edges times their ψ, and divide by the whole door size. A 1000 × 2100 mm door with a 700 mm panel of Up 0.8 under Ug 1.1 glass and a Uf 1.3 frame gives 1.23 W/m²K.
- Does a panel make a door warmer than glass?
- Usually: a panel of Up 0.8 in place of 700 mm of Ug 1.1 glass takes the example door from 1.36 to 1.23 W/m²K, by having less glass and less glass edge.
- What ψ value should I use for the glass edge?
- 0.08 W/mK for an aluminium spacer in a wood or PVC frame and 0.11 in a metal frame with a thermal break, the defaults of EN ISO 10077-1; warm-edge spacers come lower, from their maker's data.