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Guide to Double Glazing

Last Updated Jun 25, 2014 · Written by Rob Schneider


With energy efficiency being a top priority today, double glazing is often in the news. Everyone agrees that double glazed windows and doors improve energy efficiency, but is double glazing worth the extra cost? The answer depends on a variety of factors. This guide to double glazing will help you decide if it is worth it to you.

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What is Double Glazing?


As the name implies, double glazing is basically a window or door that has two panes of glass installed in its frame rather than just one. However, its energy efficiency doesn't stem from the extra thickness, but from the gap between the panes of glass. The empty space between the panes is what provides insulation from heat and cold.

The importance of insulating glass cannot be over-estimated. According to numerous independent studies, windows are responsible for more heat loss or gain in a building than any other part of the building. How much more? The facts may surprise you:
  • In summer, an unshaded window can allow up to 100 times as much heat to enter the home as an insulated wall. Put another way, a square metre of single glazed glass in summer can produce as much heat in the home as a single bar radiator.
  • In winter, heat loss through windows can be 10 times greater than through insulated walls. In a typical home, windows alone can account for up to 40 percent of heat loss.
The rate of heat conduction (the rate at which heat passes through a barrier) is measured in "U-Values". The U-Value of a 3mm thick pane of glass has been calculated to be 5.9. In contrast, 2 panes of 3mm glass with a 6mm gap between them are rated 3.1. This is roughly half the U-Value of a single pane of glass, which equates to half the amount of heat gain in the home.

The frame also makes a dramatic difference in the U-Value of windows and doors. An ordinary aluminium window frame, for example, has a U-Value of 10.0, while a timber frame has a U-Value of just 2.8.

Heat loss is calculated as an "R-Value", which represents the ability to prevent (or Resist) heat from escaping. In colder climates, the R-Value is of more significance than the U-Value. The Australian Fenestration Rating Council (AFRC) has calculated that when the temperature dips 15 degrees, heat loss through 70 square metres of single glass is the equivalent to a loss of 6,510 watts of energy in a single night. Simply by installing double glazed windows with low R-Ratings can cut that energy loss in half and save the equivalent in heating costs.

Getting Quotes for Double Glazed Windows and Doors


Aside from the factors mentioned above, other factors affect the U-Values and R-Values of double glazed windows and doors. Some of these include:
  • Argon gas inserted between the panes of glass increases their thermal efficiency even further.
  • Manufacturers of some aluminium framed windows and doors have made dramatic improvements to their U-Values.
  • uPVC framed double glazed windows are reported to have better U-Values than aluminium framed windows.
Because their U-Values and R-Values are so important, your first question when getting quotes for double glazing should be, "What are this product's U-Values and R-Values?" After that, you can start comparing quotations and balancing supply and installation costs in the scale against potential energy savings.

Rather than sift through all the glaziers in your area individually, why not get 3 quotes the easy way with our hipages.com.au Get Quotes service? Just fill in the details once (not forgetting to ask about thermal ratings) and a dedicated member of our staff will forward your request for quotes to 3 glaziers in your area. Nothing could be easier and better yet, the service is free.
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