The number that settles arguments: U-value
A window's U-value measures how much heat it lets through: lower is better. Tired old glazing sits far above any modern unit, a standard A-rated double glazed window sits comfortably low, and triple glazing sits lower still. The big prize, the leap that transforms cold rooms and heating bills, is captured by the move from old to modern, whichever modern you pick.
That is why the right way to compare quotes is to ask every installer for the U-value of the unit they are pricing, not the label on the brochure. Acoustic, toughened and self-cleaning glass each step the price up for their own reasons, and none of them is the same claim as better insulation.
When the third pane earns its keep
Triple glazing makes most sense where the conditions are hardest: exposed plots, north-facing rooms, bedrooms over passageways, and houses being pushed toward very low energy use, where every surface is being squeezed. The pane of glass nearest you stays warmer, which reads as comfort when you sit beside it on a cold evening.
It also suits homes moving to low-temperature heating, where cutting heat loss lets the whole system run gentler, the same logic that applies to radiators and insulation with a heat pump. What it does not automatically buy is silence: for traffic noise, well-specified acoustic double glazing often beats standard triple, because noise and heat answer to different physics.
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Price both. The premium for triple varies enough between installers that a rule of thumb is less useful than two numbers on the same page, and on a whole house, where a three-bed in uPVC casements lands around £7,500 in double glazing, the difference becomes real money.
If the house is average and the budget has a better home, modern A-rated double is the rational buy; if you are doing the windows once in twenty years on an exposed site, the third pane is cheap insurance. Either way, compare quotes from trusted window and door installers with the U-value written on each, and the decision mostly makes itself.
Compare window and door quotes
Up to three trusted window and door installers quote for the work. Free, no obligation.
Compare window and door quotes