ENERGY EFFICIENCY
Warmer rooms, lower bills, and a quieter home.
New windows and doors do more than smarten up the front of the house. They cut the heat you're losing, take the edge off outside noise, and make rooms comfortable to sit in year-round. Here's how it's measured — and what it means for you.
THE BASICS
What's a U-value?
A U-value measures how much heat escapes through something — in this case, your window or door. It's the rate of heat loss per square metre, so the lower the number, the less heat you lose and the better the insulation.
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That's the opposite of most ratings people are used to, where higher means better. With U-values, low is good. An old single-glazed window might sit around 5.0; a modern double-glazed unit is comfortably under 1.4.
FOR COMPARISON
Where different glazing sits.
Figures are typical whole-window U-values in W/m²K and vary by frame, glass and unit make-up. Bars are shown to scale for comparison.
THE OTHER RATING
Window Energy Ratings, A++ to E.
You'll also see windows given a Window Energy Rating (WER) — a traffic-light style band like you'd find on a fridge or washing machine. It rolls heat lost, heat gained from the sun, and air leakage into one simple grade. It runs from A++ at the top down to E.
A++
A+
A
B
C
D
A window can carry a higher band even with a moderate U-value if it captures more warmth from the sun. Both measures tell part of the same story.
THE RULES
What the regulations ask for.
Replacement windows: 1.4 or band B.
Under current Building Regulations (Part L) in England, replacement windows in an existing home must hit a U-value of 1.4 W/m²K or better, or carry a Window Energy Rating of band B or above. Either route is fine — they're two ways of proving the same thing.
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It's the installer's job to make sure of this, not yours. Everything we fit meets or beats these standards as standard, and your FENSA certificate is your proof it's all been done by the book.
Regulations summarised from Approved Document L (England) and correct at the time of writing. Different rules apply to new-build properties and in Scotland. We'll always confirm the right specification for your project when we survey.
WHY IT'S WORTH IT
What you actually get from it.
Lower heating bills
Less heat escaping means your heating works less hard to keep rooms warm. The savings build up quietly, every winter, for as long as the windows are in.
A quieter home
Better-sealed, multi-pane glazing dampens traffic, trains and general outside noise. A real difference if you're on a busier road.
Kinder to the planet
Using less energy to heat your home means a smaller carbon footprint. A small bit of the bigger picture, but it counts.
No more cold spots
That draught you feel by the window, or the room that never quite warms up — modern units and tight seals take the chill off and make the whole room usable.
Less condensation
Warm inner panes mean far less of that morning misting on the glass — which in turn means less damp and mould around the frames.
Added kerb appeal
Efficient windows are a genuine selling point. A good energy rating is one of the things buyers now look for, and it shows.
GOES HAND IN HAND