Upgrade impact
Current window heat loss
0 kWh/year
After upgrade
0 kWh/year
Annual bill saving
£0
Annual CO₂ saving
0 kg
Payback and recommendation
Methodology
How the window upgrade model works
The calculator uses simplified whole-window U-values: around 5.0 W/m²K for single glazing, 3.0 for older double glazing, 1.4 for modern double glazing, and 0.8 for triple glazing. Frame type and exposure add a modest adjustment because poorer frames and exposed sites can make a visible difference to realised heat loss and comfort.
Annual heat loss is estimated with a simplified heating-degree style approach rather than a room-by-room SAP model. The goal is to screen whether glazing upgrades are likely to be a high-impact bill saver or more of a comfort, condensation, and acoustic improvement project.
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