Energy calculator
What would new windows save you?
Tell us roughly what windows you have and how you heat your home. We'll work out the heat they lose in a year, and what our double or triple glazing would save.
Each year, about
£94 less on heating
1,442 kWh less mains gas · 260 kg less CO₂
Heat lost through 13.0 m² of windows: 2,271 kWh now, 973 kWh with double glazed glazing (57% less).
How we work it out
A window's U-value is the heat it loses per square metre for every degree between inside and out. Over a year that is the U-value × the window area × the degree days × 24 hours. We use about 2,600 degree days, typical for Cumbria and the Scottish Borders.
Our U-values are our own (double glazed 1.2, triple 0.8; building regulations ask for 1.6). The figures for your windows now are typical ones for their kind, and the boiler is taken as 90% efficient. Carbon uses the UK government's conversion factors, roughly.
It counts the windows only, not draughts round old frames, which new windows also stop. It's a guide: our survey measures your windows and gives you the real figures.