The short answer is no: A-rated windows and A++-rated windows are not the same. A++ windows are significantly more energy-efficient, with a Window Energy Rating (WER) that is at least 40% better than an A-rated equivalent. The WER scale runs from G (lowest) to A++ (highest), and the rating is calculated by the British Fenestration Rating Council (GOV.UK, 2026).
The key variable that decides the rating is the overall energy balance, which combines U-value (heat loss), solar heat gain, and air leakage. A-rated windows typically have a U-value around 1.4 W/m²K, while A++ windows achieve a U-value of 0.8 W/m²K or lower (Energy Saving Trust, 2026). A++ windows apply to homeowners prioritising maximum thermal efficiency, often in new builds or deep retrofits. They do not apply if your budget is tight or if your existing frames are suitable for secondary glazing instead.
A-rated windows meet current Building Regulations
Building Regulations Part L in England and Wales currently require replacement windows to achieve a minimum WER of band C, though most installers supply A-rated windows as standard. An A-rated window has a WER of at least 40, meaning it saves around £115–£135 per year on energy bills compared to single glazing (GOV.UK, 2026). For a typical semi-detached home with 10 windows, upgrading from D-rated to A-rated can cut heat loss by roughly 30%. A-rated windows are widely available and typically cost £400–£600 per window installed, depending on frame material and size (TrustMark, 2026).
A++ windows offer the highest energy savings
A++ windows achieve a WER of 60 or higher, meaning they are at least 50% more efficient than A-rated windows. They typically use triple glazing, low-emissivity coatings, and warm-edge spacer bars to reduce heat loss to a minimum. A++ windows can save an additional £30–£50 per year compared to A-rated windows in a typical home (Energy Saving Trust, 2026). However, they cost more, typically £600–£900 per window installed. The payback period is longer, often 15–20 years, making them best suited for homes with very high heating demand or for those aiming for net-zero standards.
How to check and compare window ratings
Every rated window sold in the UK must display a BFRC label showing the WER band, U-value, and solar heat gain coefficient. You can compare directly: an A-rated window has a U-value around 1.2–1.4 W/m²K, while an A++ window has a U-value below 0.8 W/m²K (BRE, 2026). Always ask for the BFRC certificate before buying. For most homes, A-rated windows are sufficient for compliance and cost-effectiveness. Choose A++ only if you plan to keep the windows for 20+ years or if you are aiming for a Passivhaus or EPC A-rated home. Check your installer is registered with MCS or FENSA for certified installation.
A worked example
A 1930s semi-detached house in Manchester with 12 m² of single-glazed windows upgrading to A++ triple glazing costs roughly £6,500 after the 0% VAT saving that runs until March 2027. The same upgrade to A-rated double glazing costs around £4,200. The A++ windows save an estimated £195 per year on heating bills compared to single glazing, while the A-rated alternative saves roughly £130 per year according to the Energy Saving Trust. Over 25 years the A++ windows deliver around £4,875 in total savings, more than covering the extra upfront cost. The payback period for A++ windows is roughly 14 years versus 16 years for A-rated windows. Neither upgrade qualifies for the BUS grant which covers heat pumps only, but some homeowners on means-tested benefits may access ECO4 funding for glazing improvements.
| Item | Figure |
|---|---|
| Upfront cost after grants | £6,500 for A++ or £4,200 for A-rated |
| Yearly savings | £195 for A++ or £130 for A-rated |
| Payback period | 14 years for A++ or 16 years for A-rated |
| 25-year lifetime savings | £4,875 for A++ or £3,250 for A-rated |
What homeowners often get wrong
Many homeowners assume that A-rated and A++ windows deliver nearly identical performance, but the difference in energy efficiency is substantial. Here are three common mistakes to avoid.
- Believing A++ is just a marketing label The misconception is that A++ is a gimmick from premium brands. In reality A++ windows must meet a WER of at least 60, compared to 40 for A-rated, which means they lose less than half the heat through the glass. Choosing A-rated over A++ in a 1930s terrace could cost you an extra £65 per year in heating bills.
- Thinking all triple glazing is A++ Some homeowners assume that triple glazing automatically earns an A++ rating. In fact poorly designed triple glazing with a U-value above 1.0 W/m²K may only achieve band B or C. Always check the BFRC label or ask for the WER certificate before buying.
- Ignoring the frame material A common mistake is choosing A++ glass but fitting it into aluminium or uPVC frames with poor thermal breaks. The frame can account for up to 30% of the window area and a substandard frame can drop the overall WER by two bands. Composite or timber frames with warm-edge spacers are essential to preserve the A++ rating.
Quick reference
- A-rated windows have a Window Energy Rating of at least 40 while A++ windows require a rating of 60 or higher on the BFRC scale.
- A++ windows achieve a U-value of 0.8 W/m²K or lower compared to roughly 1.4 W/m²K for A-rated windows.
- Building Regulations Part L in England and Wales require replacement windows to meet a minimum band C, so both A and A++ exceed the legal standard.
- Upgrading from A-rated to A++ windows in a typical semi-detached house saves an extra £65 per year on heating bills.
- Check the BFRC energy label on any new window because some triple glazing products only achieve band B or C despite costing more.
Frequently Asked Questions
The difference is energy efficiency: A++ windows are at least 40% better than A-rated. The Window Energy Rating scale from G to A++ is calculated by the British Fenestration Rating Council.
No, Building Regulations Part L only require a minimum WER of band C, and most installers supply A-rated windows as standard. A++ windows are for maximum efficiency in new builds or deep retrofits.
A-rated windows save around £115–£135 per year on energy bills compared to single glazing, according to GOV.UK. For a typical semi-detached home, upgrading from D-rated to A-rated cuts heat loss by roughly 30%.
