Energy cost calculator

According to Institut für wirtschaftliche Ölheizung, old windows represent the weakest link in the house. Depending on their structural condition, they can account for loss of between 10 and 40 litres of heating oil per square metre of window area every year. For an average window area of 30 m2 in a single-family home this amounts to between 300 and 1,200 litres of heating oil. Save yourself this waste. By installing new windows, you can minimise the energy loss through your windows. Replace your windows now and save doubly!

Calculate energy costs

, W/m²K
, € / Ltr. Heating oil
, € /10 kwh

Key figures

K value or U value listing by construction type, change in K value requirements for windows in accordance with German Thermal Insulation Ordinance (WSVO) and German Energy Saving Ordinance (EnEV)


WSVO I K 3.5 W/m²k for windows

WSVO II K 3.1 W/m²k for windows

WSVO III K 1.8 W/m²k for windows (equiv. K value 0.5, check via calculation of solar heat gains)

EnEV K 1.3 W/m² for windows (usual calculation value, not limit value)

Sources: K values, Sanco Glass Book, WSVO 1977 / 1984 / 1995 and EnEV 2002.

We cannot guarantee that the old windows exhibit the stated thermal transmittance values (K or U values). 
Furthermore, we cannot guarantee that the specified savings potential will actually be achieved.