What new double glazing saves

The headline figure is the one most people want: replacing single glazing with A-rated double glazing saves up to around £140 a year on a typical semi-detached house, according to the Energy Saving Trust. The savings boxes in the calculator above scale that figure to the number of windows you set, alongside a rough payback period, so you can see how the saving relates to the spend. Treat it as an upper guide rather than a promise, because the exact number depends on your house size, your region and, above all, what you are replacing.

That last point matters most. The big saving comes from swapping out genuine single glazing, which loses the most heat of any window. If you already have working double glazing, replacing it with new double glazing will improve comfort but save far less on the bill, because most of the gain was captured years ago. The honest way to read the calculator is as a comparison against single glazing, which is the scenario the Energy Saving Trust figure describes.

Heat, noise and the U-value

Beyond the pound figure, two physical changes drive the result. The first is heat loss. Modern double glazing cuts the heat escaping through your windows by roughly 30 to 50% compared with single glazing, because the sealed gap, the low-E coating and the argon fill all slow the transfer of warmth. The measure of this is the U-value, where lower is better. The second is noise: a sealed double glazed unit can cut outside noise by up to around 36 dB, which is the difference that makes a home on a busy road noticeably quieter.

Source: web/lib/research/u-values-wer.md. Lower U-values lose less heat; A-rated double glazing is the value sweet spot.

The table shows why the jump from single to A-rated double glazing delivers the saving, and why the further jump to triple is smaller. If you want the science behind these numbers, our guide to U-values explained sets out how the rating is measured and what counts as good in 2026.

Will the saving justify the spend

This is the real decision, and it is purely a glazing question, not a general bills question. Up to £140 a year against a window job that runs into the thousands means energy saving alone rarely pays the windows off quickly. The honest case for new double glazing is the combined return: the saving, plus the comfort, plus the quiet, plus the look and the value it adds to the home. People who buy windows expecting the bill saving to cover the cost are usually disappointed; people who weigh up the whole package are not. Our guide on whether double glazing is worth it works through that fuller sum.

To pair the saving with a real price, run your spec through the uPVC window calculator for the value route, the aluminium window calculator for slim modern frames, or the timber window calculator for a period home. Each shows the cost next to the same energy figure.

The verdict on energy savings

If you are coming from single glazing, A-rated double glazing is worth it on the energy side, and that gain stacks on top of the comfort, noise and resale benefits. If you already have decent double glazing, the energy case alone is weak, and you should be buying for other reasons.

Worth it Going from single to A-rated double glazing is Worth it for the energy saving, though comfort and quiet carry the case.

I am straight with people: do not buy windows to clear your energy bill, because the maths rarely works on its own. Buy them because the house is warmer, quieter and worth more, and treat the £140 a year as the bonus on top. Coming off single glazing is where the saving is real; swapping old double glazing for new is a comfort job, not a bill job.

Tom Bradley, FENSA-registered installer