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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

Answers to the questions we're asked most.

  • 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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