Window energy ratings use the same coloured-bar label as fridges and washing machines. The scale runs from E at the bottom to A++ at the top. It is a useful shorthand, provided you know what goes into it.
What the rating measures
A Window Energy Rating considers the whole window, frame and glass together, and balances three things:
- Heat lost through the window, expressed as its U-value
- Heat gained from the sun through the glass, known as solar gain or g-value
- Heat lost through air leaking around the seals
The result is an energy index in kilowatt-hours per square metre per year. A window that gains as much heat from the sun over a year as it loses scores zero and is rated A. Positive scores earn A+ and A++.
| Band | Energy index (kWh/m² per year) |
|---|---|
| A++ | 20 or more |
| A+ | 10 to under 20 |
| A | 0 to under 10 |
| B | -10 to under 0 |
| C | -20 to under -10 |
Rating or U-value?
A U-value measures heat loss alone: the lower, the better. An energy rating also rewards solar gain. Two windows with the same rating can therefore behave differently. One may insulate superbly but admit little sun; another may insulate less well but collect more free heat.
For a shaded or north-facing window, the U-value is the figure that matters. For a sunny elevation, the rating gives a fairer picture. Building Regulations accept either: band B or better, or a U-value of 1.4 W/m²K or lower, for replacement windows.
What we fit
Our uPVC windows are made from a six-chamber 70mm profile and glazed with argon-filled, low-emissivity units and warm-edge spacers. They are A-rated as standard with double glazing and reach A+ and beyond with triple glazing, with U-values as low as 0.8 W/m²K.
