All properties lose heat through their windows. But energy-efficient glazing keeps your home warmer and quieter as well as reducing your energy bills. That might mean double or triple glazing, secondary glazing, or just heavier curtains.

How much you could save
The benefits of energy-efficient windows
How energy-efficient glazing works
What to look for
Windows in period properties
Alternatives to double glazing
Installing energy-efficient glazing
Doors and conservatories


    How much could you save?

By installing double glazing in an entirely single glazed house you could save the following each year:

Energy rating


Semi detached

Mid terrace



A rated £130 - £175 £90 - £120 £80 - £105 £60 - £80 £50 - £65
B rated £120 - £160 £80 - £110 £70 - £95 £50 - £70 £40 - £60
C rated £120 - £150 £80 - £105 £70 - £90 £50 - £65 £45 - £55

These savings are for typical gas heated homes.


The benefits of energy-efficient windows

  • Smaller energy bills.
  • A smaller carbon footprint.
  • A more comfortable home: energy-efficient glazing reduces heat loss through windows and means fewer draughts and cold spots.
  • Peace and quiet: as well as keeping the heat in, energy efficient-windows insulate your home against outside noise.
  • Reduced condensation: energy-efficient glazing reduces condensation build-up on the inside of windows.

The costs and savings for energy-efficient glazing will be different for each home and each window, depending on the size, material and installer. Double glazing should last for 20 years or more.

To get a better idea of how much you could save by replacing your windows, use the Energy Saving Calculator at the Glass and Glazing Federation’s website, developed with the Energy Saving Trust.


  How energy-efficient glazing works

Double-glazed windows have two sheets of glass with a gap between them, usually about 16mm, to create an insulating barrier that keeps heat in. This is sometimes filled with gas. Triple-glazed windows have three sheets of glass, but aren’t always better than double-glazed windows: to choose the most energy-efficient window look for the BFRC rating.

Energy-efficient windows come in a range of frame materials and styles. They also vary, depending on:

  • how well they stop heat from passing through the window
  • how much sunlight travels through the glass
  • how little air can leak in or out around the window.

  What to look for

  • Glass: The most energy-efficient glass for double glazing is low emissivity (Low-E) glass. This often has an unnoticeable coating of metal oxide, normally on one of the internal panes next to the gap. This lets in light and heat but cuts the amount of heat that can get out. 
  • In between: Very efficient windows might use gases such as argon, xenon or krypton in the gap between the sheets of glass.
  • Pane spacers: These are set around the inside edges to keep the two panes of glass apart. For maximum efficiency, look for pane spacers containing little or no metal – often known as ‘warm edge’ spacers.

Frame materials

For all frame materials there are windows available in all energy ratings.

  • uPVC frames last a long time and can be recycled.
  • Wooden frames can have a lower environmental impact, but require maintenance. They are often used in conservation areas where the original windows were timber framed.
  • 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. This reduces the need for maintenance and keeps the frame weatherproof.

Energy rating

Some window manufacturers show the energy efficiency of their products using an energy rating scheme from A to G - like the one used for appliances such as fridges. The whole window (the frame and the glass) is assessed on its efficiency at retaining heat. The scheme is run by the British Fenestration Rating Council (BFRC). Find more information on the BFRC website.



Replacement windows will be more airtight than your original frames, so condensation may build up in your house due to the reduced ventilation. If your house does not have much background ventilation, look for replacement windows with trickle vents incorporated into the frame to let in a small amount of controlled ventilation.

If you start to see condensation building up around your windows, there may be a damp problem in your home. As a general rule damp occurs when there is inadequate ventilation, inadequate heating, inadequate insulation or a combination of these. If you’ve started to notice condensation in between the panes of glass in your double-glazing units then it is likely that the seal is broken, and the unit will need to be replaced.


  Windows in period properties

If you live in a conservation area or a listed building there may be restrictions on what you can do to your windows. There are a number of non-intrusive window insulation options available for historic homes such as heavy lined curtains, shutters, secondary glazing and sealed blinds. However, each historic building is considered individually so check with your local council to see what options are available to you.


Conservation areas

These areas are of special architectural or historic interest, meaning that any work you carry out on your home must preserve or enhance the character of the area. This does not necessarily mean you cannot replace your windows, but might mean you will need to get windows that complement the character of the building and area. Double glazing can be made to look like your building’s original windows, but for any changes you do need to contact your local council’s conservation officer for guidance.


Listed buildings

Listed buildings have tight controls on what you can change on the outside and sometimes the inside as well depending on their grading. Old sash windows in historic properties can be protected not only for their appearance but also the materials and methods used to make them. But secondary glazing can be a non-intrusive way of insulated historic windows from the inside, and may be granted permission.

There are other ways to make historic buildings more energy efficient but you will need to consult and apply for permission from your local planning authority.

See the Historic Scotland website for ways to make a historic home more energy efficient.


Sash windows

Sash window units are common features of period properties and can be a design feature. They consist of two vertically sliding frames, but are often badly fitting and made of single pane glass so have poor insulating qualities.

If you want to insulate your sash windows there are a number of alternatives to conventional double glazing. If you want to keep the design and look of the sash windows, there are units available that are in keeping with the original design; these are fitted and sealed to prevent draughts and incorporate double glazing to reduce heat loss. The frames don’t need to be plastic, but can be metal or wood with an insulated core.

An increasing number of double glazing companies offer double glazing in period properties. Replacing sash windows can be expensive, though, so good-quality secondary glazing may be worth considering.


  Alternatives to double glazing

If you can’t install double glazing – for example if you live in a conservation area, period property, or listed building – you can install secondary glazing, or use heavy curtains, or do both.


Secondary glazing

A secondary pane of glass and frame can be fitted inside the existing window reveal. This won’t be as well sealed as a double-glazing unit, but will be much cheaper to fit, and will still save energy. Low emissivity glass will improve the performance of secondary glazing.

Secondary glazing kits are available for the proficient DIYer to install themselves - these cuts down on costs and are a non-intrusive way of insulating your windows.


Heavy curtains, sealed blinds and shutters

Curtains lined with a layer of heavy material can reduce heat loss from a room through the window at night and cut draughts. Hollow blinds, fitted into place with a sealed frame, and sealed shutters will also help cut draughts and keep your heat in for longer.


  Installing energy-efficient glazing

Before installing double glazing, check with your local planning office if you:

  • live in a conservation area
  • have an article 4 direction on your property, removing the right of permitted development
  • have a listed building.

Most people will have double glazing fitted professionally.


Finding an installer


England and Wales

In England and Wales, the easiest way to make sure that your windows are fitted to the government’s building regulations standards is to choose an installer who is registered with one of the official Competent Person schemes. Installers registered with these schemes will give you a certificate when the job is finished which states that your new windows have been fitted in compliance with the regulations. Registered schemes for windows can be found at the competent person website.

If you use an installer who isn’t registered with one of these schemes, you will need to apply for building control approval before installing the window.  Go to the Planning Portal site to find out how to apply for building control approval.

As secondary glazing is more specialised than double glazing, there isn’t currently a central body that certifies these installations. The best thing to do is use the websites above to search for glazing companies and check whether they also provide secondary glazing. Remember always to get a number of quotes to get the best deal.


  Doors and conservatories


Energy-efficient doors

Like any other part of the home, doors can be insulated and draught-proofed to prevent heat from escaping. Buildings regulations state that installing a new door requires approval from the relevant buildings control body, and new external doors now generally contain integrated insulation to reduce heat loss and comply with the regulations.

A properly fitted new external door should include an effective draught-proofing system. Existing doors can be improved by fitting draught-proofing strips around the seals and the letterbox. Fitting draught-proofing to the doors and windows will save the typical household between £10 to £50 a year.



Even the best-quality glazing loses heat more quickly than an uninsulated cavity wall. This means that conservatories are not thermally efficient and should not be heated. Provided they are never heated, and the doors between the conservatory and the heated house are kept shut in cold weather, they can actually reduce heat loss by acting as an extra insulating layer outside your house. You can make the most of this by installing a sealed sliding door, and sealed blinds or heavy, lined curtains to separate the conservatory more effectively from the rest of your house.

If you heat your conservatory, any benefit you may have had will soon disappear along with the heat that escapes into the outside air. Double glazing, blinds and shutters can all reduce the amount of heat wasted, but it is not possible to bring a conservatory up to the thermal standard of even an averagely insulated room. If you want to save energy and money, save your conservatory for the summer.