01/09/2026
When you're comparing window quotes, the energy rating is a key tool in your decision making, so it’s important to understand it.
The BFRC scale runs A++ down to E, and it beats a bare U-value because it rolls three things into one score: heat lost through the whole window, free heat gained from the sun, and air leakage around it. Anything A or above is "energy positive" across a year it gains more warmth from sunlight than it loses.
Two things to check on any quote: that the rating covers the whole window, frame and all, not just the glass, and that it clears the current Building Regs minimum.