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The ultimate guide to energy-efficient windows and doors

Draught-proofing your home is a constant battle between stopping draughts, letting people and pets come in and go out as they please, and creating adequate ventilation.

Gaps in the fabric of your home let cold air in and warm air out, whether they’re official gaps like doors and windows, or unofficial ones like cracks between the floorboards or around pipework through the external walls. So they’re one of the first areas to tackle when you’re trying to make your home more energy efficient.

Luckily, stopping draughts can be comparatively cheap and easy, and often offers 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 from creating sudden shivers, you’ll find you can comfortably lower the setting on your thermostat, which could save you another £10 each year. [1]

Here’s our handy guide to creating your very own sausage dog draught excluder.

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


Your home particularly needs good ventilation in places where there are open flues or fires, and 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.

DIY draught proofing your home OVO insulation

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

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 inside door works particularly well if you live in a Victorian terraced home where the front door opens onto a passage that stays much 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.

How can I reduce the heat lost through windows?

The easy, but expensive, answer is to install double glazing. It creates highly energy-efficient window insulation, and you can choose from a range of materials, all equally effective: uPVC, wood, aluminium, steel or composite.

However, 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 in each individual case. For example, if you have sash windows, these 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 up 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.

DIY home insulation

How much would double-glazing save me on my heating bills?

Double glazing can take a while to pay back your investment, but it’s long lasting (20 years or more) and can certainly make a home warmer and more comfortable, as it reduces draughts and cold spots. Fully insulated windows can also cut down your carbon footprint, shut off external noise thanks to double glazing’s soundproofing qualities, and reduce condensation.

These figures from the Energy Saving Trust show how much you could save each year if you live in a typical gas-heated home in England, Scotland or Wales, with single-glazed windows throughout, and replaced them all with double-glazed ones.

Energy rating Detached Semi detached Mid terrace Bungalow Flat
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


To find a more ideas to help you save energy in your home, try our Energy Saving Calculator, which was developed to help you cut your costs of electricity in your home.

What is A-rated double glazing?

Windows are rated by the independent British Fenestration Ratings Council (BFRC) on a scale of G up to A+, where A+ represents the most energy-efficient windows and G is the least efficient. So an A-rated double-glazed window would have reached the second-best level of energy efficiency.

The scale is called the WER (Window Energy Ratings), and it assesses the performance of door and window insulation based on:

  • How effectively it stops heat escaping (the U-value).
  • Its solar heat gain (g value) – i.e. how much sunlight can pass through the glass.
  • How little air can leak out through or around all the components of the door or window.

So a window’s overall rating depends on the total combined energy efficiency of its frame, double-glazing units and airtightness.

The WER label shows the rating by using a set of coloured bars, much like the energy efficiency labels found on electrical appliances. It also shows the product’s U-value, which is the measure of how easily heat can pass through it – the lower the better.

A- or A+-rated windows could include these features, which can increase a product’s energy efficiency but may also make it more expensive:

  • Low emissivity (Low-E) glass – this is the most energy-efficient glass. It often has an invisible coating of metal oxide, which lets light and heat in but reduces the amount of heat that can escape.
  • Gas in the gaps – the most energy-efficient doors and windows have argon, xenon or krypton in the gaps that keep the glass panes apart.
  • Pane spacers – these are set between the inside edges of the panes to keep them apart. The best ones (warm edge spacers) contain little or no metal.

DIY home insulation

I live in a conservation area – can I double-glaze my home?

If you live in a conservation area, an area of special architectural interest, or a listed building, any work you carry out must preserve or enhance the character of your home. You’ll need to talk to your local council’s conservation officer and ask which specific restrictions apply to your property. You may well be allowed to install double glazing, but it may need to be in a style and material that suits the building and replicates the original windows.

You’ll also need to check with your local planning office if there is an article 4 direction on your property, as this limits your permitted development rights.

If you are definitely not allowed to install double glazing, you may be able to achieve greater energy efficiency with blinds, shutters, heavier curtains or secondary double glazing.

What is secondary double glazing?

It’s a secondary pane of glass fitted on the inside of the existing window. It can’t be sealed as effectively as an integral double-glazed unit, but can still help to keep heat in, and cold air and noise out. It’s also much cheaper to fit, and experienced DIY-ers can buy kits to cut costs even further.

You can improve the performance of secondary glazing by using Low-E energy-efficient glass.

How do I find a double glazing installer?

Visit the Glass and Glazing Federation website to find double glazing installers in your area who’ve signed up to their consumer code. This should ensure you get excellent service, and if you’re not happy with the work you can use the Federation’s free reconciliation service.

If your home is in England or Wales, you could choose an installer who is registered with an official Competent Person scheme. If so, once they’ve finished the work, they’ll give you a certificate stating that your new doors and/or windows comply with the scheme’s regulations.

In Scotland, you’ll need to check with your local authority’s building standards office.

*Source and notes for graphs and table

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