The type of glazing you choose can help you to:

• reduce heat loss during winter
• reduce heat gain during summer.

U-values

Windows consist of glazing and framing. Both components contribute to the overall performance of the window, 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 unwanted heat and cold. Low U-values can improve your comfort levels and reduce your energy costs.

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 heat gain in winter as well as summer, it is generally not recommended for sun control in Victoria. Low-e glass will complement double glazing to reduce winter heat loss through windows, however. 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, it may be possible to mimic the properties of a double-glazed window. Glazing treatments are also a popular solution for improving the energy efficiency of heritage windows, as they maintain the existing character.

Glazing films for existing windows

There are 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 include;

• 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.

Questions to ask your window supplier

Your window supplier or installer can provide valuable ideas and industry knowledge, but it is important that you ask the right questions.

Window Energy Rating Scheme

The Window Energy Rating Scheme (WERS) gives a star rating to a window's glazing and frame energy performance, making it easier to compare different windows and decide which is best for your needs.

Read more

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