Double glazed windows use two sheets of glass with a gap between them which creates an insulating barrier, whilst triple glazed windows have three sheets of glass. Both options can deliver a high level of energy efficiency. It is not the case that you have to use triple glazing to gain the most energy efficient window.
Energy efficient windows are available in a variety of frame materials and styles. They also vary in their energy efficiency, depending on how well they stop heat from passing through the window, how much sunlight travels through the glass and how little air can leak in or out around the window.
Some window and door manufacturers helpfully use a window energy rating scheme to show the energy efficiency of their product. This is similar to the one you may have seen on appliances such as your fridge, or washing machine. A-rated windows are the most efficient. To check a window’s energy efficiency before you buy, look at the energy label.
The costs and savings of double glazing will be different for each home and each window, depending on the size, material and installer.
The table below shows the potential saving on energy bills that can made when going from single to double glazing. It assumes all windows are replaced with B rated double glazing in a typical house (three bedroom semi detached home). Savings will also vary depending on how much you currently pay for your heating fuel, these savings are based on a gas heated home. More information on the assumptions can be found on our energy saving assumptions page.
If you want to find out how much you could save replacing your windows, use the Glass & Glazing Federations (GGF) Energy Saving Calculator, developed in collaboration with the Energy Saving Trust.
Replacement windows come in a range of styles and designs and there are particular features you should look out for to increase energy efficiency.
To find the right windows for your home, ask yourself these questions:
When choosing replacement windows, you can check its energy efficiency by looking at the Energy Saving Trust Recommended logo and BFRC energy label. The Energy Saving Trust endorses any windows rated B or above. The higher the energy rating, the more energy efficient it is. Unfortunately, at the moment there is no obligation for window manufacturers to label their products, however by opting for a high rated window you know you will be buying the most efficient.
For a list of all windows and their frame material and energy rating, visit the BFRC website.
Double glazing has two layers of glass with a gap of around 16mm between them. There’s also the option of triple glazing, which has three layers of glass. Both A rated double and tripled-glazed windows are available.
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. It lets sunlight and heat in but cuts the amount of heat that can get out again.
Very efficient windows might use gases like argon, xenon or krypton in the gap between the 2 sheets of glass.
All double glazed windows have pane spacers set around the inside edges to keep the two panes of glass apart. For a more efficient window, look for pane spacers containing little or no metal – often known as “warm edge” spacers.
The BFRC window energy rating scheme checks all the components to ensure the final window achieves the energy efficient standard claimed. This means that you just need to look for the A-G ratings and remember A is best! Alternatively, just look for the Energy Saving Trust Recommended logo which will only be found on glazing that is B rated or above.
The frame you choose will depend on your home and your personal taste. For all frame materials there are windows available in each energy rating.
Because replacement windows will be more airtight than the original single glazed frames, condensation can build up in your house due to the reduced ventilation.
If there is not a sufficient level of background ventilation in the room some replacement windows will have trickle vents incorporated into the frame that let in a small amount of controlled ventilation.
Condensation can sometimes occur on the outside of new low-e glazing. This is because low-e glass reflects heat back into the home and as a result the outside pane remains cool and condensation can build up in cold weather – this isn’t a problem.
When you plan an installation, you need to know about building regulations and what to do if double glazing doesn’t suit your property, as well as how to maintain your windows.
When you think about replacement glazing, you need to make sure your windows are installed correctly and comply with all the relevant regulations.
Under building regulations in England and Wales new and replacement windows must meet certain energy efficiency requirements:
However, if you live in a conservation area, have an article 4 direction on your property or have a listed building, additional regulations are likely to apply. Before you do any work, make sure you check with your local planning office.
An article 4 direction removes the right of permitted development, meaning that you will have to apply for planning permission before replacing any windows. This is often applied in Conservation areas.
To make sure regulations are complied with, there are certain rules about the way you can install windows:
FENSA guarantees that its installers and frames comply with building regulations. To find a FENSA registered installer, visit the FENSA website.
Certass is another scheme that registers and approves installers. To find a Certass registered installer visit the Certass website.
Ask your installer when you will get a certificate when installation is completed, which demonstrates the installation has been completed in compliance with building regulations.
If you can’t install double glazing – for example if you live in a conservation area or in a listed building – you have other options:
Curtains lined with a layer of heavy material can reduce heat loss from a room through the window at night and cut draughts.
They will save some energy, but should only be used as a short term measure.
Secondary glazing works by fitting a secondary pane of glass and frame, inside the existing window reveal.
This is likely to be less effective than replacement windows. The units tend to be not as well sealed, however it is considerably cheaper than double glazing.
It is also an ideal solution if you are unable to fit double glazing because you live in a conservation area or in a listed building.
Low emissivity glass is available for secondary glazing, which will improve the performance.
As double glazing should last for more than 20 years or more, you’re unlikely to upgrade often so it’s worth installing windows with a good energy rating straight away. Looking for the Energy Saving Trust Recommended logo is an easy way to ensure you are buying windows with a good energy rating.
Sometimes your windows will need maintenance, for example if the seal within the double glazed unit between the two sheets of glass fails. This leads to a build-up of condensation (misting) between the panes, and you may need to replace the glass unit – but you can usually do this without replacing the frame, which would be considerably more expensive.
As with installation, double glazed window units should only be replaced by registered installers or checked through the building control process.