How to select energy efficient glazing

The type of glazing you choose can help you to keep the heat in during winter while also keeping the heat out in summer.

Windows consist of glazing and framing. Both components contribute to the overall performance of the window, which is called a U-value. U-values measure the amount of heat passing through a glazed unit in watts; the lower the U-value, the more energy efficient your window is. In your home, you should aim to use windows with low U-values because they will be more effective at keeping out any unwanted heat and cold.

Selecting glazing for new windows

Double or triple glazing

Double glazed windows are very energy efficient, as they can reduce heat loss or heat gain by almost 30% in comparison to single-glazed aluminium windows. Triple glazing performs even better than double glazing and is ideal for the colder Victorian climates.

Low emittance glass (Low-E glass) 

Emittance is a measure of how much radiant heat a material absorbs and emits. As low-e glass reduces solar gain in winter as well as summer, it is not generally recommended for sun control in Victoria and is more appropriate for complementing double glazing to reduce winter heat loss through windows. In Victoria, adding a low-e coating to the internal pane of glass will help to make your house warmer in winter.

Secondary glazing for existing windows

Secondary glazing can be retrofitted to existing windows through the addition of an extra pane of glass or clear acrylic fitted to an existing single glazed window. Secondary glazing can be attached through magnetic strips or built onto the existing frame, and is often a cheaper alternative to double or triple glazing. Depending on the product and its ability to create an air space between the existing window and the second layer, they may be able to mimic the properties of a double glazed window.

Secondary glazing treatments are a popular solution for improving the energy efficiency of heritage windows, as they maintain the existing character.

Glazing films for existing windows

There are also a range of magnetic and transparent films on the market that can be fitted either to the frame or the glass of an existing window. The glass can also be treated to reduce the amount of solar energy lost through it. Some glass treatments reduce heat gain and the amount of light in winter as well as in summer. Common products are:

Toned glass, in which a tint is applied to the glass during manufacture to reduce the amount of heat transmitted through it.

Reflective coatings, which can be applied to new and existing windows. These tend to stop greater amounts of heat gain than some toned glass.

Tips for selecting double glazing

The gap between the two pieces of glass should ideally be at least 12mm and filled with Argon gas for maximum performance.

If you are using double glazing to reduce noise, a gap of 50-100mm should be used. Note that this will slightly reduce the thermal performance of the window.

Remember that the type of window frame is just as important as the glazing. Find out how to choose the right window frame .

Questions to ask your window supplier

When purchasing new windows, it's important to ask your window supplier the right questions.

What is the specified U-value of the windows?

If you are renovating or building, your windows may require an energy rating. Your supplier should ensure that the U-value supplied matches the required U-value stated on the energy rating. Remember the lower the U-value, the better.

How will the windows be shaded in summer?

It is vital to have external shading to stop the hot summer sun from entering your home through your windows. This will keep you home significantly cooler during the summer months. Find out more about external shading for summer.

More information

The Window Energy Rating Scheme (WERS) rates a window’s glazing and frame energy performance in the form of stars. This will help you to compare the relative energy performance of different windows and decide which type is best for your needs. Find out more by using the Window Energy Rating Scheme.