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Window Energy Ratings (WER)

The Window Energy Rating scheme rates windows from A++ to E based on overall thermal performance. Understand what the ratings mean and how to choose.
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A++ to E Scale
BFRC Certified
Part L Compliant

What each energy band means for your home.

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Band A++ & A+

The highest-performing windows. Net energy gain — the window lets in more solar energy than it loses through heat transfer. Typically triple glazed with warm-edge spacers.

Band A & B

Excellent performance. Most quality double glazed windows with Low-E glass and argon fill achieve Band A or B. Significantly exceeds Building Regulations minimum.

Band C (Minimum)

The minimum acceptable rating for Building Regulations compliance under the alternative WER route. Equivalent to approximately 1.4 W/m²K U-value.

Band D & E

Below current Building Regulations minimum. Often found in older double glazing from the 1990s-2000s. If your windows are rated D or E, replacement will yield significant energy savings.

Expert Knowledge

How Window Energy Ratings Work

The Window Energy Rating (WER) scheme is administered by the British Fenestration Rating Council (BFRC). It provides a simple A++ to E scale that combines three factors into a single rating:

1. Solar Heat Gain (g-value): How much free solar energy the window lets in. Higher is better — it means your windows are passively heating your home.

2. Thermal Transmittance (U-value): How much heat escapes through the window. Lower is better — it means less energy wasted.

3. Air Leakage (L-value): How much warm air escapes through gaps in the window. Lower is better — it means a tighter seal.

The WER formula balances these three factors. A window could have an excellent U-value but poor solar gain and still achieve a lower rating than a window that's slightly less insulating but captures more solar energy.

Pane Relief and WER:

Our sealed units are a key component in the WER equation. By specifying Low-E glass with optimal solar gain characteristics and argon fill for low U-values, our units help window manufacturers achieve Band A or above consistently.

Building Regulations let you demonstrate compliance using either U-value (≤ 1.4 W/m²K) OR WER (Band C minimum). The WER route can be advantageous for south-facing windows where solar gain contributes positively to the rating.

Common Questions

Frequently Asked Questions

Everything you need to know about our double glazing repair and replacement services across the South West.

  • WER ratings are not mandatory, but they provide an alternative compliance route for Building Regulations Part L. You can demonstrate compliance through either a U-value calculation or a WER band rating. Many consumers find the A-E scale easier to understand than U-values.

  • Our standard sealed units with Low-E glass and argon fill typically contribute to Band A or above when fitted in modern frames with good thermal breaks. The final WER depends on the complete window (frame + glass + seals), not just the sealed unit.

  • The WER label is issued to the finished window (frame + glass), not to sealed units alone. Your window manufacturer or installer will provide the WER certificate. We provide U-value and g-value data for our sealed units to help them calculate the final rating.

  • A similar scheme exists for doors (DSER — Door Set Energy Rating), but it's less widely used. Part L U-value requirements apply to all glazed doors regardless of whether they have a DSER rating.

High-Performance Sealed Units

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