How much heat is lost through windows?
A typical home loses around 10% of its overall heat through the windows. However, if your home only has single glazing or poor window insulation, then you could be losing much more than this.
The amount of heat lost also depends on the number of windows in the house and how well they're maintained.
What can I do to prevent heat loss through windows?
One obvious measure is to replace windows and doors, including frames, with double or triple glazing. This reduces heat loss through the windows and resolves any issues with draughts as well. This can be expensive, especially if you get the whole house done.
According to the Energy Saving Trust, a set of A-rated double glazed windows for a semi-detached house will typically cost around £15,000. However, along with making your home more comfortable, it could save you up to £140 a year on your energy bills.
How does double glazing work?
As the name suggests, double glazing achieves heat savings by having two panes of glass about 16 millimetres apart. This works best if there's a vacuum between the panes, or some manufacturers use a special gas instead, often argon. This is known as a sealed unit.
Having a deeper and accessible cavity of up to 100mm or more can sometimes be an option - the larger gap protects against external noise such as aircraft and traffic, and some suppliers offer triple glazing sealed units.
What types of window frame are available?
You can find energy-efficient windows made with any of the following main frame materials:
- uPVC, or plastic, windows generally contain steel for added strength. There's no need to paint uPVC window frames, which saves on maintenance costs. They can look quite basic though.
- Composite windows and doors consist of an inner timber frame coated with a protective layer. They’re generally available in a variety of colours but can be more expensive than uPVC.
- Wooden frames are the greenest option but require a fair bit of maintenance. They’re often used in conservation areas where the original windows had timber frames.
Aluminium or steel frames are sleek and long-lasting but they can be prone to condensation.
Does the energy efficiency rating apply to windows?
There's an A to G energy efficiency rating system that applies specifically to windows. Look for the BFRC energy efficiency label and ensure you use an authorised retailer.
It's worth remembering, however, that some uPVC doors and window frames are no more energy-efficient than wooden ones. The inefficiency of old windows and doors has as much to do with the glazing and draughts as with the material that the frames and non-glazed panels are made of.
If you want completely new window frames, consider triple glazing or low-emissivity (Low-E) double glazing. This is glass with a special coating which enables a better thermal performance than that of normal glass.
Should I change the size of the opening casements in my windows?
While you may want to save money by reducing the number of opening casements, or by specifying fewer and larger opening casements, this isn’t a good idea. It will create security and ventilation issues.
Larger opening casements make it harder to have a suitably low level of ventilation, and if they are accidentally left open, they create more of a security risk. Having said that, it's a good idea to have at least one larger opening casement in each room, as this can be used as a means of escape if there is an emergency.
How do I know my double glazing is working?
From time to time, sealed units can fail and will need replacing. You can usually tell when there's a problem as condensation or droplets will appear between the two panes of glass. Most suppliers offer a guarantee - usually 10 years - and will replace windows free of charge if they fail within the guarantee period.
Can I fit double glazing if I live in a conservation area?
If you live in a conservation area or in a listed building, there may be restrictions on what you can do to your windows. uPVC replacement windows are typically not allowed. Consider these options instead:
Slim double glazing
You may be able to replace your existing pieces of glass with sealed units, if your frames can accommodate them. Slim units are now available that are suitable for use in many original window frames without the need for replacements. These can have an overall thickness of as little as 12mm with a gas-filled cavity and 5mm perimeter seal designed to fit into Georgian-style windows to maintain the visually slim glazing bars. A traditional glazer should be able to fit them.
Secondary glazing
Secondary double glazing is another option, and one which is often overlooked. It's also a potential DIY option, and a strong option for use in conservation areas, as well as locations that suffer from noise pollution, such as under an aircraft flight path or near a main road. The basic concept is to put up a second wall of glazing on the indoor side of the existing pane.
Is double glazing my only option to prevent heat loss?
Double glazing is just one option. There are alternatives and some are cheaper. For many of the options, the services of a joiner or handyman might be needed. But, to save money, you can carry out many of them as DIY solutions. Options include:
Window film
Putting one of the temporary but purpose-made transparent films - a polymer membrane - on your windows is one way to create a very cheap form of double glazing. Alternatively, products like Ecoease secondary glazing attach to your windows with strong magnetic strips, so you can remove them when the weather gets warmer.
Silicone sealant
If you have small cracks or gaps around the window, you can fill these with a waterproof sealant. It’s durable, long-lasting and cheap to buy from DIY stores, but it can be a bit tricky to apply if you’re a novice.
Thermal curtains
Curtains lined with thick material can act as a barrier between your window and the rest of the room, reducing heat loss. Hollow blinds, installed with a sealed frame, can also help to improve room insulation.
What about temporary 'glazing' in winter?
Putting one of the temporary but purpose-made transparent films - a polymer membrane - on your windows is one way to create a very cheap form of double glazing. Alternatively, products like Ecoease secondary glazing attach to your windows with strong magnetic strips, so you can remove them when the weather gets warmer. Generally, you don't need many tools to do this, although a hairdryer is usually one of them - this creates the heat to make the film shrink until it's taut and smooth. You will also need double-sided tape - which is normally provided with the product - to adhere the film to the indoor side of the window frame.
What about keeping cool in summer?
Insulation isn't just about keeping your home warm when it's cold outside, it's also about keeping it cool when it's hot outside. External shutters are rare in the UK, but popular in France and other southern European countries. These provide added security, and protect against overheating in summer.
