What Are Window Energy Ratings (WER) and How Do They Differ from U-Values?
When choosing new windows or doors, you’ll often see terms like energy rating and U-value.
Both measure how well a product keeps heat inside your home — but they do it in different ways. Understanding the difference helps you choose designs that save energy, lower heating costs, and keep your home comfortable all year round.
What Is a Window Energy Rating (WER)?
The Window Energy Rating (WER) is an overall score that shows how energy-efficient a window is.
It’s based on the familiar A++ to G scale, where A++ is the best and G is the least efficient.
The rating is calculated using three factors:
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U-value – how well the window keeps heat in
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Solar gain – how much natural warmth from sunlight it lets in
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Air leakage – how airtight the seals and frame are
WER gives you an easy-to-understand comparison between different windows, so you can quickly identify which products offer the best performance.
What Is a U-Value?
A U-value measures the rate of heat transfer through a material — essentially, how much warmth escapes through your window.
It’s expressed as W/m²K (watts per square metre per degree Kelvin).
The lower the U-value, the better the insulation.
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1.2 W/m²K or lower is excellent for double glazing
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0.8 W/m²K or lower is exceptional and typical of triple glazing
U-values are often used by architects and builders because they provide precise technical detail about thermal performance.
WER vs U-Value: The Key Differences
| Feature | Window Energy Rating (WER) | U-Value |
|---|---|---|
| Measurement type | Overall window performance | Heat loss only |
| Includes solar gain and air leakage | Yes | No |
| Better when… | Rating is higher (A++) | Number is lower |
| Ease of comparison | Simple for homeowners | More technical |
In simple terms:
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WER gives an overall view of energy efficiency.
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U-value provides a detailed measurement of insulation.
For most homeowners, WER is the easier way to compare products — but both are important for long-term energy savings.
Why These Ratings Matter
Windows and doors with strong energy performance help to:
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Keep your home warmer in winter and cooler in summer
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Lower your energy bills
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Reduce your carbon footprint
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Improve comfort and sound insulation
At Home Build Doors, our aluminium, composite, and flush PVC ranges are engineered to deliver high WER ratings and low U-values — combining sleek design with exceptional efficiency.
Ready to Upgrade?
Explore our full range of high-performance windows and doors at Home Build Doors and discover how better insulation can enhance comfort, reduce energy use, and transform your home.
Start your quote today at homebuilddoors.co.uk.