At a glance
Windows let in useful warmth and light in winter, but in warmer weather sometimes this can be too much. Heat gain through an unshaded window in summer can be 100 times greater than through the same area of insulated wall. In winter windows can allow up to 40 per cent of your heat to leak out. This means you'll be using more energy to keep your home comfortable and paying higher energy bills.
Install double glazing or window films
Double glazing on windows and skylights helps keep heat in or out and also reduces outside noise. Double glazing is not just for cold climates—it's very useful for air-conditioned homes to keep cool air in. How well your double glazing will work can depend on how it is installed, what type of window frames you have, and the climate you live in.
Installing window films can be another cost effective option for reducing solar heat gain through existing windows. Some window films can halve the overall amount of solar energy passing through the window.
Your Home has more information about the many different types of glazing.
Install energy-efficient window frames
Look for the WERS (Window Energy Rating Scheme) label on products when installing windows.
The Heating Star rating shows how well the windows keep heat in. The Cooling Star rating shows how well they stop the heat from entering. Some doors and skylights also have a WERS rating. A 5-star rating is the maximum, and a sign of the best performance.
Depending on your climate, you may choose to focus more on heating or cooling, although in most climates you really want to focus on both to maximise year-round comfort.
Choose windows that can be opened wide and skylights that open to encourage natural ventilation. Just make sure they're airtight when closed.
Install window furnishings
Snug-fitting curtains and blinds on windows can prevent heat loss and gain as they trap a layer of still air next to the window. Window furnishings are a good way to deal with problems with existing windows. Heavier fabrics and multiple layers of fabric give the best thermal protection.
If you're installing blinds, look for an insulating fabric and ensure they're well-fitted to restrict air movement around the window to prevent unwanted heat loss or gain. For an energy-efficient option honeycomb or cellular blinds are an excellent choice as they trap air within cells and act like a double-glazed window.
If you're in a hot climate, use external blinds and awnings to provide shade in summer. Blinds which are white or near-white on the outside or have a reflective surface will reflect more heat back outside.
Fitted pelmets will prevent heat loss above the windows. Pelmets can be made of any material as long as it creates an air barrier. If you're renting you may be able to make temporary pelmets from cardboard, timber or other stiff materials. Bubble wrap or a thick piece of fabric are also options. Pelmets need to be flush against the wall and sitting above the track, and reach to or past the curtain. Most pelmets reach over the curtain. However, you can also build a hidden or near-invisible pelmet as a single flat strip that sits behind the top of the curtain and just reaches its back edge.
An alternative to sealing the top of the curtain is to seal the base and sides to prevent cold air being drawn in. Floor-length curtains will stop air entering at the base. The curtains can be held in place by weighting the hems so that they stay in contact with the floor. If your curtains are just short of floor length, two heavy fabric-and-sand 'sausages' such as those used to block gaps under doors can hold the lower curtain edge trapped between them. Temporary tape, magnetic tape or Velcro can hold the curtain sides in place.