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What is Thermal Rating Register?
There are several energy rating schemes for windows, the most widespread being those operated by Thermal Rating Register, the British Standards Institute, British Fenestration Rating Council, and each, works in the same way.
The two most common are the Thermal Rating Register (TRR) and the British Fenestration Rating Council (BFRC) which are effectively the same thing for consumers: they are competing brands that calculate and issue identical Window Energy Ratings (WER). They use the exact same mathematical formula and physics to measure window efficiency.
Using the “Supermarket Analogy”
They are just different brands selling the exact same certified standard:
“Think of it like buying groceries. A ‘Traffic Light’ nutrition label on a loaf of bread means the exact same thing whether you buy it from Tesco or Sainsbury’s. BFRC and Certass TRR are just the Tesco and Sainsbury’s of window testing.”
Compare the Core Mechanics
Show that under the hood, they do identical work. You can present this using a quick overview:
| Feature | Thermal Rating Register (TRR) | British Fenestration Rating Council (BFRC) |
| Parent Body | Certass (UKAS-accredited) | GGF / FENSA family |
| Visual Label | A* to G “Rainbow” label | A++ to E “Rainbow” label |
| What it Measures | Whole-window performance | Whole-window performance |
| Formula Used | Heat Loss + Solar Gain + Air Leakage | Heat Loss + Solar Gain + Air Leakage |
| Legal Status | Fully satisfies UK Building Regs | Fully satisfies UK Building Regs |
Key Talking Points
- Same Math: Both systems take the window’s U-value (heat loss), G-value (solar gain), and L-value (air leakage) and plug them into the official UK government formula to generate the final grade.
- Equally Legal: A window rated “A” by the Certass Thermal Rating Register carries the exact same legal weight for Building Regulations compliance as a window rated “A” by the BFRC.
- Different Club Membership: If an installation company is registered with Certass, they use the Thermal Rating Register. If they are registered with FENSA, they typically use the BFRC. Neither is “better”; they are just tied to different trade certification bodies.
Letter ratings are given to window products based on the energy performance of the whole window, including the frame material, frame design, glass type and other components. An A rated window is more energy-efficient than a C rated window. The letter rating is calculated using a formula that takes into account the window product’s overall thermal efficiency, air leakage and solar gain (how much heat from the sun passes through the window).
https://www.ggf.org.uk/myglazing/news/window-energy-ratings/
The labels below are typical of the labels that you should see on your windows. They are supported by registered bodies which audit the window installers;
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| Certass Thermal Rating Register Scheme website: www.certass.co.uk Tel. No. 0845 838 | BSI Kitemark Scheme for WER Website: www.bsigroup.com Tel. No. 0845 076 5602 | British Fenestration Rating Council WER Scheme Website: www.brfc.org Tel. No. 020 7403 9200 |
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