New windows: Calculate an estimate of the heat savings
Old and new windows can have different insulating performance. The calculator combines the window area and energy data and shows how the change can affect the heat loss and heating cost of your home.
Result
Use figures for the whole window
The U-value of the glazing does not necessarily describe the whole window. The sash, frame and joints also affect the heat loss. So use the total value of the window when that is what the calculator asks for.
The contribution from the sun can differ before and after a replacement. Orientation and choice of glass matter. The result shows whether solar gain is included, or whether the calculation only describes a change in transmission loss.
Guide to comparing windows
Measure the windows to be replaced
The same facade can have several window types. Work out the area and energy data for the relevant groups, so a small modern window is not treated like a large old window.
Example of transmission difference
If the total U-value is improved by 1 W per m² and degree on 20 m² of windows, 2,500 degree days give about 1,200 kWh less transmission loss in the simple calculation. Other energy contributions are not included in this example.
Replacing windows can also be about maintenance and comfort. These factors are not automatically a cash heat saving. Enter the total project price, and consider comparing several solutions. Installation, sealing and the condition of the building must be assessed specifically when you get quotes. Use the insulation savings calculator if you are also looking at other parts of the building envelope.