What Is a Window or Door Energy Rating?
In the UK, window and door energy ratings are a straightforward way to compare how energy-efficient a product is. Most ratings are issued by the British Fenestration Rating Council (BFRC) and follow a scale from A++ (most efficient) down to E or G (least efficient). These ratings factor in how well a product retains heat, resists drafts, and even how much solar heat it allows in.
The rating system helps homeowners:
- Lower heating bills
- Improve indoor comfort
- Reduce carbon emissions
According to the Energy Saving Trust, upgrading to energy-efficient glazing can save up to £155 per year on heating costs for a typical semi-detached house (source).
The National Fenestration Rating Council (NFRC) also operates a voluntary programme in the U.S. that tests, certifies, and labels products using metrics like U-factor and Solar Heat Gain Coefficient (SHGC), which are also used in UK evaluations.
Key Energy Performance Terms Explained
Understanding these values will help you compare products confidently:
- U-Value: Indicates how much non-solar heat passes through the product. Lower values mean better insulation. UK Building Regulations typically require windows to achieve a U-value of 1.4 W/m²K or better (as per Approved Document L). NFRC values reflect the entire window including frame and spacer.
- Solar Heat Gain Coefficient (SHGC): Measures how much solar radiation is admitted through the window, absorbed, and released as heat inside the home. A low SHGC is ideal for warm climates or south-facing windows to reduce overheating.
- Air Leakage (AL): Measures the amount of air that passes through gaps. A lower AL rating means better sealing and less heat loss. Ratings assume proper installation.
- Visible Transmittance (VT): The fraction of visible light that enters the space through the glazing. Higher values allow more daylight in.
- Light-to-Solar Gain (LSG): The ratio of VT to SHGC, indicating how efficiently daylight is admitted without contributing to heat gain.
- Condensation Resistance (CR) (optional): Describes how well the window resists the formation of condensation on interior surfaces.
How Are Energy Ratings Calculated?
Energy ratings are determined by assessing:
- Thermal insulation (U-value)
- Solar gain (SHGC)
- Airtightness (AL)
- Visible light transmittance (VT)
The BFRC rating label balances these factors into a single grade (A++ to E). This makes it easier to compare products, even for non-experts. NFRC labels used in ENERGY STAR® certified products provide a similar breakdown in North America.
EPC Ratings and Whole-Property Energy Performance
Energy Performance Certificates (EPCs) measure a home's overall energy efficiency, with ratings from A (most efficient) to G (least efficient). They are mandatory for homes being sold or rented. The certificate includes:
- Estimated energy costs
- Environmental impact rating
- Recommendations for improvement (e.g., low-E glass, insulation upgrades)
As of 2021, all new rental properties are expected to meet at least a band C by 2025, and all existing tenancies by 2028 (gov.uk).
Improving your glazing can directly enhance your EPC rating. Replacing outdated windows with A+ rated double or triple glazing is among the most impactful upgrades.
What Energy Rating Should You Look For?
- A++ Rated: Ideal for new builds and passive house standards
- A to B Rated: Excellent performance for most properties
- Below C Rated: Not compliant with latest regulations; should be upgraded
Current Building Regulations (June 2022 update) require new and replacement windows to meet a minimum U-value of 1.4 W/m²K.
Internorm & Energy Ratings: Premium Performance
AT-ECO supplies high-performance window systems from Internorm, Drutex, and other leading manufacturers. Many of our Internorm triple-glazed products exceed A++ standards with U-values as low as 0.62 W/m²K.
Case Study: At Stockhouse Farm in Surrey, our Internorm triple-glazed systems were installed across a series of award-winning A++ Passive House terraced homes. These high-performance windows and doors deliver outstanding thermal efficiency, achieving an A++ energy rating while maintaining a stunning, traditional design aesthetic. The project was recognised with the Evening Standard Eco Living award for its exceptional energy performance and design quality.
Real-World Energy Savings: Appliance Comparisons
Beyond windows and doors, energy efficiency applies across the home. Consider these examples from the Energy Saving Trust:
| Appliance Type | A-Rated Annual Cost | G/F-Rated Cost | Potential Annual Saving |
|---|---|---|---|
| Washing Machine | £61 | £107 | £46 |
| Dishwasher | £67 | £134 | £67 |
| Fridge Freezer | £37 | £112 | £75 |
| Total Potential | £188 | ||
Energy-efficient choices throughout the home compound the benefit of upgraded glazing.
How to Check Ratings Before You Buy
- Look for BFRC or NFRC labels showing U-value, SHGC, VT, and more
- Check for ENERGY STAR® or EU Energy Label certification
- Scan QR codes (if available) for more detailed product specs
- Always ask for FENSA certification to ensure compliant installation
What You Can Do to Be Greener
- Use eco modes on washing machines and dishwashers
- Switch off devices instead of leaving on standby
- Upgrade lighting and insulation where possible
- Schedule a home energy audit for targeted recommendations
Conclusion: Energy Ratings Empower Better Decisions
Energy performance ratings make it easier to compare windows, doors, and even household appliances. When you understand what the labels mean, you gain control over comfort, costs, and carbon footprint.
