The ultimate guide to energy-efficient windows and doors

27 August 2020 | Matt Mostyn

energy efficient windows

Draught-proofing your home is a constant battle between stopping draughts, allowing ventilation and letting people (and pets!) come and go as they please.

Whether they’re gaps in doors and windows, cracks between the floorboards, or gaps around pipework through external walls, spaces in the fabric of your home let cold air in and warm air out. And when you’re trying to make your home more energy-efficient, door and window gaps are one of the first things to tackle.

Luckily, stopping draughts can be comparatively cheap and easy, and often gives immediate results.

Draught-proofing your home could save you between £25 and £50 on your heating bills each year. And once you’ve stopped all those cold draughts giving you the shivers, you’ll find you can comfortably lower the setting on your thermostat, which could save you another £10 each year.

On the flip-side, completely sealing every single gap can result in stuffy, germ-ridden, polluted air in your home. Warm air can also hold much more moisture than cool air – so you could be creating ideal conditions for condensation and mould.

Your home particularly needs good ventilation where there are open flues or fires, and in rooms that produce a lot of moisture, like bathrooms, shower rooms, kitchens and utility rooms.

To help you maintain a suitable balance between cosy warmth and a healthy atmosphere, this guide answers the main questions about creating energy-efficient windows and doors.

What products are available if I want to draught-proof my doors and windows?

how to insulate your windows for Winter

There are several products available that work with either doors or windows. They all seem to have several different names, depending on the manufacturer, so it’s best to chat to a sales assistant to make sure you’re getting what you want.

  • Wiper seals (also known as dirt excluders) are metal or plastic strips that have brushes or wipers attached. The brush compresses slightly when the door or window is closed, creating a seal. These come in various sizes and work well on the bottom of doors, on sliding sash windows, or anywhere there’s an uneven gap or a warped surface.
  • Compression strips, draught excluder strips or tapes are self-adhesive foam strips that can ‘give’ when they’re compressed in a narrow space. These are used when a door or window closes against a frame. It’s important to choose the right size strip; if it’s too large it can actually stop the window closing properly – the opposite of what you want.
  • Silicone sealant for windows that aren’t designed to open (but are still a bit gappy).

There are also products for specific parts of your door:

  • Flaps and brushes for letterboxes – measure your letterbox first to make sure you get the right size.
  • A metal disc on the front of the keyhole, that falls back over the gap when you remove the key.
  • Hinged flaps to fill the gap between the bottom of the door and the floor.

How can I reduce the heat lost through the external doors in my home?

When it comes to heat loss, doors are usually far worse than windows. If your home has an ill-fitting, unsealed external door, you might as well knock a 6-inch hole in it and let the warm air blow out through that!

The best way to prevent heat loss through doors is to create a double-door airlock, by building a porch or conservatory outside, or adding a second door a few feet inside the original one. This works particularly well if you live in a Victorian terraced home where the front door opens onto a passage that’s the same width as the door.

With a double-door airlock, as long as everyone remembers not to open the second door until the first one is closed, you can considerably reduce the amount of hot air lost with every exit and entrance.

Which doors are the most energy-efficient?

First, look at the technical specifications, which include:

  • Glazing – a double glazed door means double the protection. With one of these, you can make your home extra warm and extra secure, reducing draughts and cold spots.
  • U Value – this is an energy efficiency assessment. Basically, the lower the U value, the more energy-efficient the door is!

Are wood doors energy-efficient?

Timber is a natural insulator, absorbing and retaining heat – and solid wood doors offer one of the highest levels of energy efficiency compared to other door types. 

Both soft and hardwood doors are great materials, but hardwood is more dense and hard-wearing. Although it can be more expensive and less sustainable than softwood. 

Things to consider when installing energy-efficient doors 

kid looking at window in Winter

Not all energy-efficient doors are truly ‘green’. Look out for the presence of lead and CFCs. The best doors are CFC-free and made with calcium zinc-based compounds. These are less damaging to the environment, but still hard-wearing enough to mean that the door will last for years.

If, like us, you care about sustainability, it’s also worth looking at the carbon footprint created through the manufacturing and shipping of the door. If ‘going green’ is important to you, look for a certified energy-efficient door made in one location, and then delivered directly to you.

This reduces the ‘product miles’ as much as possible, cutting down on all that fuel use and time on the road. That saves you money and protects the environment at the same time. Result!

Get Government help towards insulation costs with the Green Homes Grant

Interested in getting your hands on some very useful money-saving and energy-saving vouchers? The Green Homes Grant scheme helps homeowners and landlords in England with the cost of installing everything from insulation to heat pumps to solar thermal.

The vouchers are worth up to two-thirds of the cost of making your home more energy efficient  – up to a maximum of £5,000 per household. 

Find out more about the Government’s Green Homes Grant scheme

What are the most energy-efficient windows?

Let's talk about windows now! The easy, but expensive, answer if you’re looking for energy-efficient windows is to install double-glazing. It creates highly energy-efficient window insulation, and you can choose from a range of materials, all equally effective. The main contenders are uPVC, wood, aluminium, steel or composite.

If you’re on a budget, you can achieve similar results much more cheaply, simply by sealing up gaps in single-glazed windows. Then, as and when your windows need replacing, you can consider double (or even triple) glazing on a case-by-case basis. For example, sash windows are expensive to replace, even as single-glazed units, so it might not cost much more to upgrade to double glazing.

It can also be less expensive to install secondary double glazing, which is equally effective at stopping draughts and soundproofing, but can be quite fiddly to clean.

DIY home insulation

Here are some tips for stopping those gaps:

  • Apply draught excluder strips to the edges where windows close, being careful that the strips don’t actually stop the windows shutting.
  • If there are any gaps at the junctions where window frames meet walls or window ledges, seal them with silicone mastic.
  • Metal windows can sometimes develop small gaps. Seal them with silicone gel or specialist draught strips.
  • Hang heavy thermal curtains, or add thermal linings to your existing curtains – they can be very effective as a barrier to heat loss.

Energy-efficient window materials

  • Energy-efficient windows are made of two or three glass panes sealed in a single unit, and surrounded by a frame made from uPVC, wood or another material.
  • Double-glazed windows are made of two sheets of glass with a gap between – usually about 16mm.
  • Triple-glazed windows have three sheets of glass, and two gaps. This can make them better at insulating than many double-glazed windows (but not always). 
  • The gaps between the glass panes are filled with air, or an inert gas like argon, which is completely sealed.


Low emissivity (low-E) glass is the most energy-efficient type for double and triple-glazing, thanks to a microscopic coating of metal oxide. This coating reflects heat back into the home but still lets in the light from outside.

Pane gaps

The size of the gap between the panes can affect performances – but bigger isn’t always better! 16mm is often considered optimal, but smaller gaps may actually be better in some cases. 

Performance can also be improved by filling the gap with an inert gas such as argon, xenon or krypton. 

Pane spacers

These keep the panes of glass apart. More efficient windows generally have pane spacers containing little or no metal.

Frame materials

  • uPVC frames need no regular maintenance and can be recycled
  • Wooden frames can have a lower environmental impact, but require more maintenance
  • Aluminium or steel frames are slim and long lasting, and can be recycled
  • Composite frames have an inner timber frame covered with aluminium or plastic, reducing maintenance and making them more weatherproof

How much do energy-efficient windows save?

Double glazing can take a while to pay back your investment – but it’s long-lasting (20 years or more) and can make a home warmer and more comfortable by reducing draughts and cold spots. 

Fully insulated windows can also cut down your carbon footprint, reduce external noise (thanks to double glazing’s soundproofing qualities) and also reduce condensation.

These figures from the Energy Saving Trust show how much you could save each year if you replace single-glazed windows with double-glazed ones.

Energy ratingDetachedSemi detachedMid terraceBungalowFlat
A rated£120 - £160£85 - £110£65 - £90£55 - £75£40 - £60
B rated£110 - £145£75 - £110£60 - £80£50 - £70£40 - £55
C rated£110 - £135£75 - £95£60 - £75£50 - £65£40 - £50


For more ideas to help you save energy in your home, check out our energy saving tips article, which has loads of advice to help you cut your electricity bills and reduce your impact on the planet.

How to choose energy-efficient windows

The energy performance of a window is affected by a range of factors, so it’s not always easy to choose the right window based only on how it’s made. Luckily, there’s a rating scheme to help you find the most efficient one for you.

Energy-efficient windows use an energy-rating scale from A++ to E. Both frame and glass are assessed and given a rating that indicates the overall impact of fitting that window in your home.

To choose the most energy efficient window, look for the BFRC rating – and remember, an A+ rated window is more energy-efficient than one that’s C rated. 

Windows with an energy rating will also have a u-value. While it’s not a complete measure of how efficient a window is, the u-value reflects how easily heat passes through the material. The overall label rating will give you a good indication of the window’s energy-saving potential.

Some installers also offer a recycling scheme, where they’ll take away your old windows and recycle the materials. They’ll then reduce the cost of installment in return. How about that for a clever bit of sustainable initiative-taking?!

Find out more about choosing the most energy-efficient windows with our ultimate guide to double glazed windows. 

How do I find an installer to make my windows and doors more efficient?

installer to insulate windows

First, check out the Glass and Glazing Federation to find a member who works in your area. 

In England and Wales, choose an installer who’s registered with one of the official Competent Person schemes. These installers will give you a certificate that states your new windows have been fitted in compliance with regulations. 

In Scotland, each local authority has a building standards office. Check with them first to see whether you need a building warrant for your new windows.

More smart ideas to help insulate your home

There are all kinds of ways you can improve your home’s insulation levels when it comes to roof, loft, walls, windows and doors. Browse our handy user guides to learn more!

Roof and loft insulation

We lose much of our body heat through our heads – and the same goes for your roof! As much as a quarter of the heat in uninsulated homes wafts out through the roof. Filling your loft space with insulation could be a very cost-effective way to retain heat in your home and save on your energy bills.

Find out more in our guide to roof and loft insulation

Cavity wall insulation

Looking for a cost-effective way to retain heat in your home and save on your energy bills? Filling your cavity walls with insulation could be a very good idea. It’s estimated that cavity insulation could save you up to £160 a year in heating bills.

Find out more in our guide to cavity wall insulation

Solid wall insulation

Solid walls let twice as much heat escape as cavity walls. That’s bad for your bills, and bad for the environment. But it doesn’t have to be this way! Read more in our guide to solid wall insulation

Make your own draught-excluder

Finally, here’s our handy guide to creating your very own sausage dog draught excluder!

And don't forget your lightbulbs! Switching out old incandescants for energy-saving bulbs can really make the difference. Find out more in our complete guide

Looking for other ways to save money on your energy? Check out our most affordable energy plan, Better Smart and start saving on your gas and electricity bills today. 

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