The difference between a glass figure and a whole-window figure, and why it matters when comparing quotes.
Almost every window quote says 'A-rated'. That single label hides several different measurements, and installers do not always quote the same one.
Learn the three numbers and comparison becomes straightforward.
The U-value measures how much heat passes through. Lower is better. Crucially, a centre-pane U-value for the glass alone is always better than the whole-window U-value that includes the frame — make sure two quotes are giving you the same one.
The g-value describes how much solar heat the glass lets in. High solar gain is useful on north-facing or cold rooms; low solar gain suits south-facing rooms and conservatory roofs that overheat.
The A to G rating combines heat loss, solar gain and air leakage into one band. It is a useful shorthand, but it is a band — two A-rated windows can still perform differently.
We'll state the specification and the U-value in writing so you can compare quotes properly.
Ask for the whole-window U-value. It's the fairest single figure for comparing quotes.
It depends on the price gap and the room. On a large, exposed elevation it is usually easier to justify.
Yes — a warm-edge spacer improves the edge performance of the unit and reduces cold spots at the perimeter.