What A and A+ window energy ratings actually mean
When you compare quotes for new windows, you will see letters like A, A+ or A++. They look like the labels on a fridge, and they work in a similar way. Here is what they mean, what goes into them, and what to look for when you choose.
The rating scale
Window Energy Ratings in the UK are run by BFRC, which rates windows and doors on a scale from A++ to E. A++ is the most efficient. The rating covers the whole window as it is sold, frame and glass together, not just the glass.
What goes into the rating
The rating combines three things:
Heat loss, measured as the U-value of the whole window. The lower the U-value, the less heat escapes.
Solar gain, the free heat from the sun that comes in through the glass, measured as the g-value.
Air leakage, the draughts that get through the seals.
Because it weighs up all three, an energy rating tells you more than a U-value alone. Two windows with the same U-value can end up with different ratings if one lets in more solar heat or seals better.
The minimum for replacement windows
Building Regulations in England set a floor. Replacement windows in an existing home must reach a U-value of 1.4 W/m²K or a Window Energy Rating of at least band B. An A or A+ rated window goes beyond that minimum. Since 15 June 2022, replacement windows also need suitable trickle vents under the ventilation rules, so a good installer will talk to you about ventilation as well as warmth.
What makes a window perform well
Most of the difference comes from the sealed unit and the frame. Our windows are A to A+ rated. They use argon filled 28mm sealed units, which insulate better than air, and black Swiss spacers, the strip between the panes, which cut heat loss at the edge of the glass. Better sealed windows also reduce outside noise, which matters on busy roads.
Installation counts too. A highly rated window fitted badly will still be draughty, which is why every job we do is fitted by our own directly employed team, overseen by a surveyor and registered with Assure Certification.
Questions to ask in a quote
What is the energy rating of the whole window, and is it a BFRC rating?
What is the U-value of the window?
What gas fill and spacer are used in the sealed units?
Are trickle vents included where the rules require them?
Who fits the windows, and which scheme registers the work for Building Regulations?
If you would like to compare options in person, visit the showroom at 4 Hampden Square, Southgate, or book a free survey on 020 8361 0128. More on our energy saving page and our uPVC windows.