If you’re noticing cold spots, persistent draughts, rooms that never quite stay warm, or energy bills that keep creeping up, the problem may not be your heating system at all – it could be the barriers meant to protect your home.
Windows and doors play a huge role in how your home holds on to heat, and even small weaknesses can have a big impact on comfort and energy use.
The good news is that upgrading to highly energy-efficient windows and doors is one of the most effective energy-efficient home improvements you can make.
Whether you’re comparing double glazing with triple glazing and wondering if the extra cost is worth it, or simply trying to stop draughts around an older door, this guide explains everything you need to know about highly energy-efficient windows and doors so you can make the best choice for your home.
Why Energy Efficiency in Windows and Doors Matters
Windows and doors account for a surprising amount of heat loss. External doors are often one of the draughtiest parts of any property, and depending on the age and condition of your glazing, a typical UK home loses around 10% of its heat through its windows alone. If you have single glazing or older, worn frames, the figure can be even higher.
That heat loss leads to:
1. Higher heating bills
When warm air escapes, you’re forced to turn the heating up or keep it on for longer. The most energy-efficient windows slow down heat transfer, reducing heat loss in the winter and heat gain in the summer, keeping indoor temperatures stable.
2. Higher carbon emissions
Cutting energy use isn’t just good for your wallet. It’s good for the planet. Upgrading to the most energy-efficient windows and doors is a straightforward way to lower your home’s carbon footprint.
How Energy-Efficient Windows Work
What makes a window energy efficient?
Energy-efficient windows aren’t just pieces of glass. They’re specifically engineered to slow heat loss.
Double Glazing
Now the standard energy-efficient glazing across UK homes. Double glazing uses two panes of glass to make up a window, separated by a spacer bar. The gap in the middle is filled with air or an inert, insulating gas like argon.
This gap acts like a thermal buffer, reducing heat loss in winter and keeping hot air outside in summer.
High-quality, well-installed and well-maintained double-glazed energy-efficient windows typically last 20-35 years or more – and even longer with regular cleaning, checking ventilation, maintenance and checking for damage to seals and gaskets.
Triple Glazing
Triple glazing adds a third pane of glass and another gas-filled gap, providing superior energy performance. Triple-glazed windows can have a U-value of less than 0.8 W/(m²K) – 50% better than double-glazed windows.
It does cost around 20% more but can be worth it if you live in a very cold or noisy area.
Low-E (low emissivity) Coatings
The most energy-efficient type of glass for double and triple glazing is low emissivity (low-E) glass. It has a thin metal oxide layer on one of the internal glass surfaces that reflects heat back into your home while still letting light in.
Benefits:
- reduces heat loss
- reflects harmful UV rays off the window and away from your home
- helps keep rooms cooler in summer
- reduces energy consumption and bills
Gas Fills (Argon, Krypton, Xenon)
Gas-filled windows use inert gases between the panes, to slow cold air transfer between them:
- Argon: most common, affordable, provides good insulation
- Krypton: better performance, more expensive
- Xenon: most expensive option, highest performance
This improves the overall energy efficiency of double and triple-glazed windows, helping to lower your energy bills.
Warm Edge Spacers & Thermal Breaks
Modern energy-efficient windows use warm edge spacers – pane spacers containing little or no metal – set around the inside edges to keep the glass panes apart, they reduce heat loss at the edge of the glass.
A thermal break is a barrier placed within the frame of a window or door that reduces heat transfer between the inside and outside. Thermal breaks are normally only needed when materials such as aluminium are used as the frame. This barrier helps to keep indoor temperatures stable, improve energy efficiency and reduce draughts, condensation and noise.
Quality of Frames & Seals
Even the most energy-efficient glazing won’t perform well if the frame or seals fail. Window frames and seals work hard in all weathers, so it’s no surprise they eventually wear out. Common reasons include:
- Weather and moisture: wood can swell, warp or rot in very damp conditions, and uPVC can expand and contract with temperature changes.
- Condensation build-up: moisture sitting on frames can encourage mould and gradually eat away at the frames and seals.
- Over-enthusiastic cleaning: using pressure washers might be quick, but the force of the water can cause damage.
If the seals are separate from the frame, they can often be replaced on their own. Where they’re built-in, it may be possible to replace just the glazed unit rather than the entire window.
Window Energy Ratings
Understanding Window Energy Ratings (WER) helps you choose the right energy-efficient windows for your home.
What is a U-Value?
A U-value measures how easily heat passes through a material. The lower the U-value, the better the insulation.
However, the U-value is not a complete measure of how energy-efficient a window is. The overall energy efficiency rating will give a better idea of this.
What Does an A-rating Mean?
The British Fenestration Rating Council (BFRC) is the UK’s most trusted and widely recognised rating organisation for verifying the energy performance of windows and doors. Its window energy ratings run on a scale of A++ (most efficient) to E (least efficient). The entire window is assessed to consider heat loss, draughts and solar gain.
An A-rated window:
- loses less heat
- helps lower heating bills
- reduces energy consumption
How to Read BFRC Energy Labels
On the left-hand side of the label, there’s a scale with different colours ranging from magenta for A++ down to orange for E. The lettered pointer will tell you the rating of your window.
This rating considers various factors like U-value, G-value (also known as total solar energy transmittance, measuring how much heat is transmitted through a window from the sun’s rays), air leakage, thermal heat loss and the overall energy efficiency of your window. An A++ rated window will be highly energy efficient, helping you save on heating costs.
Best Energy-Efficient Windows and Doors
What is the most energy-efficient type of window and door?
The most energy-efficient windows and doors tend to use high-performance glazing and well-insulated frames.
Top-performing window types
- Triple glazing: best overall thermal performance.
- Passive House–standard glazing: ultra-low U-value windows, often triple or vacuum glazing.
- Fixed windows: no moving parts or ability to open means they have superior sealing and the most airtight barrier.
- Inert gas fills: offer better insulation and durability than air-filled windows.
Frame Materials for Doors & Windows
- uPVC: low maintenance, durable, affordable and recyclable.
- Wooden: natural insulator, repairable and long lifespan with regular maintenance.
- Aluminium or steel: slim, incredibly strong and recyclable, may feature thermal breaks.
- Composite: consist of an inner timber frame coated with a protective aluminium or plastic layer. Excellent insulators, strong and long-lasting, plus low-maintenance. However, can be more expensive than uPVC and the frames can be chunky.
Upgrade or Replace Existing Windows
Not every draughty window needs replacing.
Retrofitting: Secondary Glazing & Draught-Proofing
Secondary Glazing
A more affordable alternative to full window replacement, can be done yourself depending on the type that is chosen. This involves adding a second pane on the inside of your existing window to increase energy efficiency. Common options include:
- Secondary glazing film: a thin, transparent plastic film that you can usually fit yourself. It’s the cheapest option but doesn’t last long and provides the least insulation compared to other secondary glazing methods.
- Magnetic secondary glazing: this uses magnetic strips or clip-fit mounting systems to hold an extra pane of glass or plastic in place on the inside of your window. It helps cut heat loss and is easy to remove or replace.
- Permanent secondary glazing: this uses made-to-measure frames (often timber or uPVC) and glazing, fitted on the inside of the window. It costs more but delivers strong insulation benefits, sometimes even better than replacing the windows. It’s also ideal for properties with restrictions, like listed buildings or homes in conservation areas.
Draught-Proofing
Good draught-proofing is one of the cheapest and quickest ways to improve comfort, cut heat loss and save money on your energy bills, without replacing your windows or doors.
For windows:
Windows that open
Stick draught-proofing strips around the frame, to close the gap between the window and frame.
There are two types:
- Self-adhesive foam strips are budget-friendly and easy to fit but may need replacing sooner.
- Metal or plastic strips with brushes or wipers attached that last longer but cost a bit more.
Make sure you choose the correctly sized strip. Too big and the window won’t close properly, too small and draughts will still sneak through.
Sliding sash windows
Foam strips don’t work well on these windows. It’s best to use brush strips or contact a professional.
Non-opening windows
Silicone sealant around the edges can seal gaps.
Thermal curtains or hollow blinds are also effective energy-efficient options for windows.
For doors:
There are four main draught hotspots on external doors:
- Keyhole: fit a small purpose-made keyhole cover.
- Letterbox: use a flap or brush-style draught excluder (measure your letterbox carefully first).
- Gap at the bottom: use a brush or hinged flap draught excluder along the bottom edge.
- Gaps around the sides and top: fit foam, brush or wiper strips like those used on windows.
Internal doors shouldn’t be draught-proofed, as you need a small gap to allow air circulation and safe ventilation around the home.
Full Replacement: What to Expect
Repairs work best for minor issues like broken handles, small seal problems or adjustment needs.
However, if window seals have failed completely, frames are warped, or energy efficiency has deteriorated significantly, this will only get worse over time. It’s better to invest in replacement windows for energy efficiency.
Replacement tends to involve:
- removing old frames
- fitting new ones
- making good interior plasterwork
- disposal of old windows and clearing of debris
Planning & Regulation
Replacement windows for energy efficiency don’t usually need planning permission unless:
- you live in a listed building
- you live in a conservation area
- you’re changing window size or installing a new window opening
- you’re adding a bay window
All replacement energy-efficient windows need to meet building regulations so it’s always best to check your local council’s planning website.
Energy-Saving Costs and Payback
Energy-efficient home improvements are an investment, but they can start paying back immediately.
Costs
Costs vary based on:
- frame material
- whether you choose double glazing or triple glazing
- whether you’re cutting in (adding) a new window or replacing an existing one
- size of window
- style and how many openings and locks are needed
- accessibility of installation
- whether scaffolding is required
A set of A-rated energy-efficient windows for a semi-detached house will typically cost around £12,000.
Typical Savings
Installing A-rated, double-glazed, energy-efficient windows, in a fully single-glazed semi-detached home can:
- save around £140 per year on your energy bills
- reduce your CO2 emissions by 380kg per year
Calculating the value of energy-efficient home improvements involves assessing the difference in U-values before and after window replacement. A standard method to estimate savings includes factoring in the temperature difference inside and outside the home.
To calculate savings from energy-efficient windows, compare the current energy bill to the previous year’s bill. Tracking monthly energy bill differences over time helps determine how long the savings achieved by fitting new windows will take to cover the cost.
If you’re looking for extra support with your energy bills and want to understand what help may be available, you can learn more here.
Maintenance and Energy-Saving Tips
Even the best energy-efficient windows don’t last forever. Over time, everyday use and the British weather take their toll.
When energy-saving window and door frames deteriorate or seals fail, your home loses more heat, your heating system works harder, and energy bills rise. These practical checks and small fixes help keep your home warmer for less.
According to Which?, the most common double glazing issues people report include:
- 34% – windows or doors becoming difficult to open or close
- 18% – windows or doors dropping over time so that they don't fit as well
- 15% – locks not working
- 12% – seals around doors or windows failing
- 9% – glass steaming up or problems with condensation
- 5% – double glazing cracking or shattering
Each of these affects insulation and can lead to unnecessary heat loss.
Keep an eye out for:
- Condensation between window panes: if you can see moisture trapped between the glass, your seals have failed. Companies offer repairs by drilling a tiny hole, removing the moisture and resealing the pane. In other cases, a glazed unit replacement or complete window replacement may be the better long-term fix.
- Draughts around frames: if you can feel cold air sneaking in, worn rubber gasket seals or loose hinges are often to blame. Replacing the seals so it’s airtight, or adjusting the hinges, can usually restore a snug fit.
- Sticking handles, locks or hinges: stiff locks or handles don’t always mean a full replacement is needed. Often, individual parts can be swapped out or hinges lubricated to get things moving smoothly again.
- Visible surface damage: look for discolouration or cracks on uPVC, oxidation or loose fixings on aluminium frames, and warping or soft, crumbly patches on wooden frames. These can be early warning signs that windows are starting to deteriorate.
- Unexplained rises in energy bills: if your heating habits haven’t changed but your bills have, heat could be escaping through ageing or failing windows and doors.
Minor issues that aren’t causing draughts, leaks or internal condensation may not need urgent work, but are worth monitoring. Small issues with energy-saving windows and doors can snowball into bigger, more expensive ones over time – and will increase heat loss.
Basic Maintenance Steps
A little bit of routine care can extend the life of both double and triple glazing and keep energy-efficient windows performing at their best:
1. Keep frames and glass clean
Use a mild detergent and soft cloth on glass and frames. Avoid harsh chemicals or abrasives that might damage coatings. Vacuum out debris from tracks and hinges so they can move freely.
2. Check seals regularly
Look along the edges of the glass. If you start to see moisture between the panes, the seal has failed.
3. Ventilate to control humidity
Open windows or trickle vents from time to time for fresh air circulation and to reduce humidity, especially after cooking, showering or drying clothes indoors. If moisture is a recurring problem, air bricks or a dehumidifier can help keep levels under control.
4. Lubricate moving parts
Use a suitable lubricant on hinges, handles and locking mechanisms once or twice a year. This helps prevent stiffness, reduces wear and keeps the window sitting correctly in the frame, which reduces draughts.
5. Inspect for cracks or damage
Cracks in glass or frames can worsen over time and reduce energy efficiency. If you spot one, it’s wise to get a professional opinion early, rather than waiting until it becomes a bigger issue.
Choosing a Reputable Installer
Confident DIYers can fit some secondary glazing systems, but removing and installing new double- or triple-glazed energy-efficient windows or a new external door should be done by a qualified professional.
There are many installation companies that will be able to fit replacement windows. However, if you want to make sure the installation work complies with building regulations, and have proof of that compliance that you can present if it’s needed in the future, it’s best to choose a FENSA Approved Installer.
FENSA is a government-authorised scheme that monitors building regulation compliance for replacement windows and doors. Every FENSA Approved Installer, from large national brands to small local companies, is assessed regularly to ensure its standards are continually maintained.
Or, choose an installer who’s registered to a competent person scheme. This is an easy way to make sure your windows are fitted to UK Government building regulations.
The Energy Saving Trust recommends getting quotes from at least three installers to help you get the best deal. You can find local, certified installers using TrustMark, which is a government-endorsed quality scheme for tradespeople. Check reviews, and make sure they give you a full quotation, so you can see exactly what you’re paying for.
For double glazing, the Glass and Glazing Federation (GGF) is a membership organisation whose members sign up to a consumer code. This means that you should get excellent customer service. If one of their members fits your windows but you’re unhappy with the work, you can use GGF’s free reconciliation service.
For more easy ways to cut heat loss and lower your bills, read our guide on how to save money on your energy bills in 2026.