The A++ window energy rating is the current top band for thermal efficiency in the UK
If you are replacing windows, you will see labels with ratings from E to A++. The A++ rating is the highest possible band for heat retention and the lowest for heat loss. This system is managed by the British Fenestration Rating Council (BFRC) and applies to the whole window, not just the glass (BFRC, 2026).
A++ is the highest window energy rating on the BFRC scale, with a U-value of 0.8 W/m²K or lower. It typically requires triple glazing, low-e coatings, and warm-edge spacers, costing £800-£1,200 per window installed but saving up to £420 per year on heating.
- A++ is the highest BFRC energy rating band in the UK.
- A++ windows achieve a U-value of 0.8 W/m²K or lower.
- Triple glazing with low-e coatings and warm-edge spacers is standard.
- Installed cost per A++ window ranges from £800 to £1,200 in 2026.
- Upgrading from single glazing can save £195-£420 per year on bills.
- The A++ window energy rating is the current top band for thermal efficiency in the UK
- What an A++ rating actually promises for your home's heat loss
- How much A++ windows cost to buy and install in 2026
- The typical annual energy savings from upgrading to A++ windows
- Quick numbers — A++ window performance and cost summary
- The payback period for A++ windows and whether it makes financial sense
- Eligibility rules and how to verify an A++ window installer in the UK
- The direct answer to "what is a window energy rating A" for homeowners
A++ windows are typically triple-glazed. They use low-emissivity coatings to reflect heat back into the room, warm-edge spacers to reduce heat loss at the edges, and insulated frames. These features together give the highest performance on the scale.
What an A++ rating actually promises for your home’s heat loss
The key measure is the whole-window U-value. A++ windows have a U-value of approximately 0.8 W/m²K or lower. That means they lose heat at a much slower rate than older windows. For comparison, a typical single-glazed window has a U-value of around 5.0 W/m²K, and standard double glazing (rated D or E) is around 2.0 to 2.8 W/m²K (BFRC, rating criteria, 2026).
The BFRC rating also accounts for solar heat gain (the G-value) and air leakage. However, the U-value is the main factor that drives energy savings. A lower U-value means less heat escapes through the window on cold days.
How much A++ windows cost to buy and install in 2026
Installed cost for a standard-sized A++ window, roughly 1.2 metres by 1.2 metres, typically ranges from £800 to £1,200 per window. A standard A-rated double-glazed unit of the same size costs between £400 and £700 (Energy Saving Trust, window replacement cost guide, 2026).
The higher cost is driven by the extra pane of glass, low-emissivity coatings, and argon or krypton gas fills. Triple-glazed A++ windows are heavier and require stronger frames, which also adds to the installation cost.
The typical annual energy savings from upgrading to A++ windows
Replacing single glazing with A++ windows can save a typical three-bedroom, gas-heated semi-detached home around £180 to £250 per year on heating bills. Upgrading from standard double glazing (rated D or E) to A++ typically saves £40 to £70 per year (Energy Saving Trust, window replacement energy savings calculator, 2026).
The savings depend on the size and number of windows, the type of heating system, and the current condition of your existing windows. If you have very draughty single glazing, the saving will be at the higher end of the range.
Quick numbers — A++ window performance and cost summary
| Metric | A++ window | A-rated window | Single-glazed window |
|---|---|---|---|
| Whole-window U-value | 0.8 W/m²K or lower | 1.2 W/m²K | 5.0 W/m²K |
| Solar heat gain (G-value) | 0.50–0.60 | 0.50–0.60 | 0.80–0.85 |
| Air leakage (m³/h/m² at 50 Pa) | Below 0.5 | Below 0.5 | Often over 2.0 |
| Installed cost per window (1.2m x 1.2m) | £800–£1,200 | £400–£700 | Not commonly installed new |
| Annual saving vs single glazing | £180–£250 | £100–£150 | — |
| Annual saving vs A-rated double glazing | £40–£70 | — | — |
Sources: BFRC, rating criteria, 2026; Energy Saving Trust, cost and savings data, 2026.
The payback period for A++ windows and whether it makes financial sense
If you replace single glazing with A++ windows, the typical payback period is 8 to 12 years. This assumes annual savings of around £200 and a total cost of £2,000 to £2,500 for an average home with three to four windows (Energy Saving Trust, payback period estimates, 2026).
If you already have standard double glazing (rated D or E), upgrading to A++ takes much longer to pay back. The payback period is often 15 to 20 years or more, because the annual savings are smaller — typically £40 to £70 per year. In that case, the financial case is weaker unless you also value improved comfort and reduced draughts.
Eligibility rules and how to verify an A++ window installer in the UK
Installers must be registered with FENSA or CERTASS to comply with building regulations for replacement glazing in England and Wales. The windows must carry a BFRC label that shows the A++ rating (GOV.UK, Part L building regulations, 2026).
You can check the BFRC online register to verify that a specific window model has a genuine A++ rating. Always ask the installer for a certificate of compliance after installation. If the installer cannot provide a BFRC-rated window label, the product may not meet the claimed rating.
The direct answer to “what is a window energy rating A” for homeowners
A window energy rating A means the window has high thermal efficiency. The whole-window U-value is around 1.2 W/m²K or better, with low air leakage and moderate solar heat gain. A++ is the highest sub-band within the A rating (BFRC, rating scale, 2026).
The rating is shown as a coloured label on the window, similar to appliance energy labels. New window installations must meet at least a B rating under Part L building regulations in England and Wales. A++ windows exceed this requirement and are the best option for minimising heat loss (GOV.UK, Part L building regulations, 2026). How to check your window energy rating label Triple glazing vs double glazing cost comparison
Frequently Asked Questions
A++ is the highest band on the BFRC scale for thermal efficiency. It means the whole window has a U-value of 0.8 W/m²K or lower, offering the best heat retention and lowest heat loss of any rating.
Installed cost for a standard 1.2m x 1.2m A++ window is £800 to £1,200 per window, according to the Energy Saving Trust (2026). This is roughly double the cost of a standard A-rated double-glazed unit.
A++ windows have a whole-window U-value of approximately 0.8 W/m²K or lower, as defined by the BFRC rating criteria (2026). This is significantly better than standard double glazing at 2.0-2.8 W/m²K.
Yes, for homes with single glazing or very old double glazing. Annual energy savings of £195-£420 on a three-bed gas-heated home can offset the higher upfront cost over time, per Energy Saving Trust figures (2026).
A++ windows have a U-value of 0.8 W/m²K or lower, while A-rated windows typically have U-values around 1.2-1.4 W/m²K. A++ uses triple glazing and advanced coatings to retain more heat.
