The cost of manufacturing a triple glazed sealed unit is higher than manufacturing a double glazed unit because there is another chamber that has to be filled with argon, extra spacer bar, another pane of toughened glass and also the cost of transportation because there is an increase in size and weight. Over double glazing, it is just a simple extra square metre which comes at £100 per square metre. What this means is that the average 4 feet (1220 mm) square window would have the 1 sq-m glass. This will result in adding about £100 to the average double-glazed window.

The Cost of a Triple-glazed Window

There is a wide range of windows with different material choices and systems. To calculate, we are going to use the standard white uPVC systems in double glazing, adding the VAT, it would come to a total of £465 (this figure is correct as of July, 2019), so the triple glazed window will come to a total of £565, which is 22% more compared to the double-glazed window. However, specialist windows, such as residence 7 windows which can be used in conservation areas, will have an additional premium on the cost. 

Heat-loss Through Triple Glazing and Windows

About 20% of heat is lost through windows in the UK. If you are in the process of changing the windows, it is a good idea to choose insulated products because it makes economic sense. You will spend more on triple glazing, but you also need to think about the savings you will be making in heating bills. You cannot expect the payback overnight, it can take some time. Many choose triple glazing because it is the most comfortable option.

Benefits of Triple Glazing

There are many benefits you can expect to get when you choose triple glazing for your home, with insulation being the main one. One thing you need to keep in mind is that all triple glazing isn’t the same. There are many triple-glazed systems out there but some of them don’t provide maximum benefit, the gaps between the glass panes should be filled with an inert gas like Argon and 16 mm. The reason why Argon is used because it reduces heat loss. If there is a reduction of this gap, then the sealed unit will have a decrease in thermal performance, unless you choose to use an expensive gas such as Krypton. The best size to use for the unit is 4 mm glass with gaps of 16 mm, which is referred to as the 4/16/4/16/4 by the glazing industry, and it adds up to 44 mm. When you compare the heat losses between the 28 mm double glazed window and 44 mm triple glazed window is a lot. Heat loss is measured in u-value. The u-value of a double glazed unit is 1.1 while triple glazed units have 0.62. This means there is a 40% improvement.

Triple Glazing Energy Rating

The first thing many people see when choosing a window is the panes it has, but it is a good idea to have a look at the Window Energy Rating (WER). This provides you with a reliable way to predict thermal efficiency when you install the units. WER is the standard method used in the UK to calculate the amount of heat that will be lost through the window.

There are different things that WER takes into account:

  • Air losses through the windows
  • The U-value, which is the thermal efficiency of the window in its entirety, which means both the glass and frame material are factored.
  • The amount of heat coming from the sun passing through the window to warm up the home. Triple glazing doesn’t offer any improvements in solar gain when compared to double-glazing, a window that has proper insulation is good at retaining heat, but doesn’t work so well when it comes to solar gain.

Triple Glazing Cost Summary

You will have to spend more on triple glazing than double glazing, and from the calculations done above, it adds 22% more onto triple glazing. What we have done above is the KJM costs, which means the figures could be lower for both double and triple glazed units when compared to the national’ glazing company. Some companies provide ‘free upgrades’ to triple glazing, but it is important to look at the starting point for the ‘base’ product. Let’s say you double the starting price then factor in the 50% discount, bringing you to a sensible point. It is a good idea to seek another quotation before making your decision.