If you’ve been looking at new windows, you may have come across window energy ratings (WER). These ratings are similar to the energy labels you see on fridges or washing machines. They tell you how efficient a window is at keeping heat in your home.
Understanding WER helps you make a better choice when buying windows, saving you money on bills and improving comfort.
What Do Window Energy Ratings Mean?
A window energy rating (WER) shows how much energy a window will save or lose in your home. The system works with a traffic-light style label, from A++ (most efficient) down to E (least efficient).
The rating is based on three things:
- Heat loss – How much heat escapes through the window (U value).
- Solar gain – How much free heat from the sun enters through the glass.
- Air leakage – Whether warm air escapes or cold air enters around the frame.
All three are combined to give an overall rating.
Why WER Matters for Homeowners
Knowing about WER is useful because it affects:
- Energy bills – Higher-rated windows keep more warmth inside, so you use less heating.
- Comfort – Rooms stay warmer in winter and cooler in summer.
- Condensation – Better efficiency reduces moisture build-up on the inside of glass.
- Resale value – Buyers prefer homes with energy-efficient features.
With energy costs still high, choosing windows with good ratings can make a big difference.
The WER Rating Scale
The WER system is straightforward:
| Rating | Performance |
|---|---|
| A++ | Best efficiency, maximum heat retention |
| A+ | Very high efficiency |
| A | High efficiency, good for most homes |
| B | Decent performance, meets regulations |
| C | Acceptable minimum under UK standards |
| D–E | Poor performance, not recommended |
In the UK, windows installed today usually need to be at least C rated under GOV.UK Building Regulations.
WER vs U Values
Both WER and U values measure energy performance, but they are slightly different:
- U values – Measure just heat loss. The lower the number, the better.
- WER – Gives an overall rating, combining U value, solar gain, and air leakage.
For example, a window might have a low U value but still only get a B rating if it doesn’t allow much solar gain. WER gives a broader picture that’s easier for homeowners to understand.
Typical Ratings for Different Windows
Different types of glazing and frames achieve different ratings:
- Single glazing – Rarely rated, very poor efficiency.
- Older double glazing – Often D rated or below.
- Modern double glazing – Usually A to B rated.
- Triple glazing – Commonly A+ or even A++.
So, if your home still has old double glazing, upgrading to new windows could easily move you up to an A rating or better.
How Are Window Energy Ratings Calculated?
The ratings are created by independent bodies such as the BFRC. They test and certify windows based on:
- Glass type – Low-E coatings, thickness, and number of panes.
- Gas filling – Argon or krypton gas between panes improves insulation.
- Spacer bars – Warm edge spacers help reduce heat loss around the glass edges.
- Frame material – uPVC, timber, or aluminium frames with thermal breaks.
- Design quality – How airtight the whole window unit is.
Only certified products can carry the official energy label.
Benefits of Higher-Rated Windows
Upgrading to A-rated or better windows offers many advantages:
- Lower heating bills – Savings can add up year after year.
- Fewer draughts – Keeps living spaces more comfortable.
- Noise reduction – Many modern designs also block outside noise.
- Eco-friendly – Using less energy reduces your carbon footprint.
- Better property value – Buyers increasingly look for energy efficiency.
For many households, the upfront cost is balanced by long-term savings.
Choosing the Right WER for Your Home
So which rating should you go for?
- Budget-conscious buyers – C or B rated windows still meet standards and improve insulation compared to older glazing.
- Long-term investment – A or A+ windows provide greater savings over time.
- Eco-friendly focus – A++ windows offer the very best performance.
It’s worth comparing costs, as the most efficient windows may cost more upfront but deliver higher savings in the long run.
WER and Building Regulations
UK law requires replacement windows to meet minimum standards. As of now:
- The minimum requirement is C rating or a U value of 1.6 W/m²K or lower.
- New builds usually require even better performance, often A rated or above.
When choosing an installer, make sure they are registered with FENSA or an equivalent scheme to ensure compliance.
Comparing Different Window Types by WER
Here’s a simple comparison to show how different styles can perform on the WER scale:
| Window Type | Typical WER |
|---|---|
| Casement windows | A – A++ |
| Sash windows | B – A |
| Bay windows | B – A+ |
| Flush fit windows | A – A+ |
Performance will vary by manufacturer, glazing, and frame design.
How to Check WER Before Buying
Before you choose windows, ask your supplier for the official WER label. You can also:
- Look for certification by the BFRC.
- Check local authority standards with LABC.
- Use installers approved by FENSA.
These steps make sure your windows meet legal standards and deliver the efficiency promised.
Summary
Window energy ratings (WER) are an easy way to compare how efficient different windows are. The scale runs from A++ to E, with A++ being the best.
For most homeowners, choosing windows rated A or above is the best balance of cost, comfort, and energy savings. If your home has older double glazing, even moving up to a B or A rating can cut bills and improve comfort.
When shopping for new windows, don’t just look at the style — always check the WER label. It’s one of the simplest ways to make sure your home is energy-efficient and ready for the future. Get in touch with one of the team using this link on any questions regarding WER rating for our windows.
