Updated June 2026 · CW Doors & Windows
What is A-rated double glazing?
Window Energy Ratings (WER) work like the labels on your fridge — A to E, with A best. Here's what each rating actually means in real heat loss, and which one is worth paying for.
The rating scale
C: Building Regs minimum — but most reputable installers don't fit C-rated.
B: Old standard, no longer common.
A: Current industry standard. U-value around 1.4 W/m²K.
A+: Better than standard, typically with low-emissivity coatings and warm-edge spacers. U-value around 1.2.
A++: Top of the BFRC scale, usually triple-glazed. U-value around 0.8.
Which rating to specify
A-rated covers 95% of UK homes. The cost-benefit drops off sharply above A.
A+ is worth specifying on north-facing rooms or properties with significant heat loss.
A++ (triple glazing) is overkill for most Leicester homes — payback is 40+ years on energy alone.
What gets you the rating
Low-emissivity (Low-E) coating on one pane.
Argon gas fill between the panes.
Warm-edge spacer bar (composite, not aluminium).
A well-sealed frame to prevent heat bypass at the perimeter.
Does the rating change the price?
On the windows we fit, A-rated glazing is our standard rather than an add-on, so the from £450 fitted price already includes it. The rating comes from the whole window: the frame chambers, the glass coating, the gas fill and the spacer bar between the panes.
If you are comparing quotes, ask each company for the rating of the full window, not only the glass. A cheap quote that uses a lower rated unit can look similar on paper but lose more heat for the next twenty years.
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