Thinking About Energy Efficient Windows? Start Here
As the colder months set in, many homeowners start to notice where their homes are losing heat, and windows are often the culprit.
Energy efficient windows are designed to keep more warmth in during winter, while also helping to prevent overheating in summer. They use modern glazing technology, improved frames, and airtight seals to reduce heat loss compared to older, single-glazed or outdated double glazed windows.
They also help with other everyday issues such as condensation and outside noise. While energy saving windows do require an upfront investment, they can pay for themselves over time through reduced bills and improved quality of life.
- How much can energy efficient windows save me on heating bills in the UK?
Up to 70% less heat loss can be achieved by replacing your old single glazing or poorly performing double glazing with modern A-rated energy efficient windows.Around £100–£300 annual savings are possible on heating bills for a typical semi-detached UK home. Detached or larger houses often see even higher savings, because they have more window area and greater energy demand. The key factors affecting your results include U-values, airtightness, total window area, property type, and existing insulation. - Should I choose double or triple glazing for my UK home?
While triple glazed windows are sometimes discussed as a good option, modern double glazing is sufficient for almost all UK homes, offering excellent thermal efficiency, comfort, and lower cost. It performs well in colder or exposed locations, north-facing rooms, or where reducing outside noise is important. - Which frame material is most energy efficient – UPVC, aluminium or timber?
UPVC’s multi-chamber design provides excellent insulation, aluminium with thermal breaks performs well but can be more expensive, and timber is a natural insulator but has a higher upkeep.Frame choice, opening style, and sealing (casement vs sash vs tilt & turn) all affect performance alongside lifespan, price, and sightlines. We recommend speaking with a Hazlemere advisor to find the right fit for your home’s needs and individual budget. - What U-value and BFRC rating should I look for?
U-value measures heat loss (W/m²K). A lower U-value is better, while the BFRC Window Energy Rating (A++ to C) shows overall efficiency. You should aim for whole-window Uw and WER targets suited to UK homes, and always compare like-for-like specs when choosing energy saving windows.
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The Science Behind Insulated Windows (Heat Loss & Solar Gain)
Insulated windows slow heat loss through conduction, convection, and radiation. Low-E coatings reflect heat back inside, gas fills reduce conductive losses, and warm-edge spacers minimise heat escape at the edges. Together, sealed units offer superior thermal performance, lower bills, and manage solar gain, letting sunlight in without losing warmth.
What is Low-E glass and how does it improve energy efficiency?
Low-E (low-emissivity) glass has a microscopic metallic coating that reflects heat back into your home while letting light through. Essentially, it keeps warmth inside in winter and reduces overheating in summer, helping windows save energy and improve comfort. Low-E coatings make modern glazing far more efficient than older units.
Gas fills & spacers (argon/xenon/krypton, warm-edge technology)
Gas fills like argon, xenon, or krypton reduce heat transfer between panes, while warm-edge spacers cut thermal bridging at the frame. They lower condensation risk, improve U-values, and help maintain a consistent indoor temperature. These subtle upgrades significantly boost energy efficiency and comfort in everyday use.
UPVC, Aluminium or Timber - Which Frame Is Most Energy Efficient?
UPVC frames insulate well, require little upkeep, and last decades. Aluminium with thermal breaks is strong, slim, and durable but less insulating than UPVC. Timber is a natural insulator, but upkeep costs are higher and energy efficiency performance can weaken as the frames don’t last as long.
Frame choice affects thermal performance, lifespan, sightlines, aesthetics, and real-world efficiency, especially when paired with quality glazing.
Which window styles are most efficient - casement, sash, tilt & turn?
Different types of windows affect energy efficiency differently through their seals. Talk to the team at Hazlemere for more information on draught proofing windows and the best energy efficient windows for keeping heat inside your home.
Styles such as casement and tilt & turn styles close tightly, minimising draughts and heat loss, while traditional sash windows can sometimes leak more air. Choosing well-sealed, high-performance styles ensures low heating costs and improved comfort in your home.
How Windows Are Rated in the UK (BFRC, WER & U-values)
UK windows are rated for energy performance using BFRC Window Energy Ratings (WER), from A++ to C, showing overall efficiency of the whole window. A U-value shows how much heat escapes and a lower number is better.
While related, WER accounts for glazing, frame, and sealing, whereas U-values focus on heat transfer. Comparing both ensures you choose genuine high performance windows, not just high-rated glass.
What is a window energy rating and how does the BFRC rating system work?
A Window Energy Rating (WER) shows how efficiently a whole window performs, from frame to glass and seals. The BFRC label runs from A++ (best) down to C, making it easy to compare products. Homeowners should use WERs to shortlist high performance windows, ensuring efficiency gains go beyond the glazing alone.
Why U-values are important (and how to read them)
U-values measure how much heat escapes through a window (lower numbers mean better insulation). Uw = whole window value, Ug = centre-pane glass only. Typical ranges:
- Single glazing: 5.0–6.0 W/m²K
- Old double glazing: 2.8–3.0 W/m²K
- Modern A-rated windows: 1.2–1.6 W/m²K. Focusing on Uw ensures true thermal performance.
What’s the difference between A, B, and C-rated windows?
A, B, and C-rated windows offer different levels of energy efficiency as part of the Window Energy Rating (WER) system. A-rated windows are the most energy efficient as they retain more heat and lower energy use, while C-rated windows will meet the minimum building regulation requirements and are the cheapest, but they won’t cut costs or improve comfort to the same level as A or B-rated windows.
The Window Energy Rating (WER) system has a scale of A+ to G, with A+ being the most efficient when it comes to saving energy. Moving from C to A-rated windows can make a noticeable difference in the comfort in your home, with fewer draughts, warmer rooms, and reduced bills.
Double Glazing vs Triple Glazing - Which Is Right for UK Homes?
For most UK homes, modern double glazing is sufficient, balancing efficiency, comfort, and cost. Triple glazing may suit colder regions, exposed sites, north-facing rooms, or homes where noise reduction is a priority, but comes with added weight, cost, and frame considerations.
The right choice depends on your property and goals, and our high performing double glazing is usually sufficient for most homes in the region.
The Bottom Line on High Performance, Thermally Efficient Windows
Choosing the right insulated windows comes down to understanding ratings and specs. We can help you compare WER and U value windows, weigh up double vs triple glazing, and provide advice on frame materials that balance energy efficiency, style, and upkeep.
As the homeowner, remember to check costs against realistic savings, plan for professional installation and ventilation, and always compare like-for-like from accredited installers, such as Hazlemere.
Our friendly and experienced advisors are ready to help you find the right window material and style to tackle rising energy costs and ease pressure on your current heating system.
By choosing carefully with Hazlemere, you’ll not only enjoy lower bills and greater comfort but also invest in windows that truly upgrade your home for many years into the future.
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Our friendly team will be pleased to help with any questions you may have.