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Argon Filled Double Glazing

Current building regulations relating to double glazing demand that windows have at least a WER (Window Energy Ratings) C rating; allowing a maximum U value of 1.6W/M2K.

To enable modern double glazing units to meet this rating, many manufacturers are now filling the cavity between the panes of glass with Argon gas instead of air.

Periodic Table showing Argon and Krypton

Argon is a chemically inert element which is used to fill double glazing units

The WER’s are based on an A-G scale similar to that used to assess energy efficiency of houses or white goods, with A being the most energy efficient, G being the least.

The U value of a window is the measure of how much heat energy escapes per square metre, every hour, for every one degree Celsius difference between the temperature inside and outside.

So what does this mean for us as the consumer? And how can we use this information in the real world, when choosing windows and doors for our homes?

The drive towards energy efficiency and low carbon emissions is pushing manufacturers to produce ever more efficient double glazed windows; which in real terms reduces heat loss from our homes, saving energy and money.

One such development available on the market today is Argon filled double glazing.


What is Argon-Filled double glazing?

The cavity between the panes of glass in conventional double glazing is filled with air, providing a substantial improvement on single glazing. The principle is that it reduces the heat transfer between panes, keeping the heat in during the winter months, and keeping the heat out during the summer.

Replacing the air with Argon, an inert gas, further reduces the heat loss, and therefore improves energy efficiency.


What are the benefits?

  • Argon is a non-toxic, colourless, odourless, chemically inert gas. It has a thermal conductivity which is just 67% of the conductivity of air.
  • The gas is six times denser than air, and this has an impact not only on thermal conductivity, but on acoustic performance as well.
  • Argon gas significantly reduces the window’s U value, saving money on heating and increasing a properties overall energy rating.
  • The higher temperature of the gas sealed in the cavity also helps to reduce the likelihood of condensation forming between the panes.


What other gases are used to fill double glazed windows?

Other gases have been considered, and used, including Krypton and Xenon. Unlike Argon they are not commercially available, at least not at a price which makes their use viable.

Krypton, while more costly than Argon, has half the thermal conductivity and is used for very thin units for specialist requirements.

Xenon is simply much too expensive to be used for windows, despite having even more efficient properties.


How about vacuum filled units?

Vacuum Insulated Glass (VIG) is another option on the market which was developed partially to solve the problem of the thickness of frames. While most buildings will accept the typical frame depth of 22-31mm, some buildings may require thinner double or triple glazed units.

The air between panes is removed to leave a near complete vacuum. The units are hermetically sealed with solder glass, and dramatically reduce heat loss from convection and thermal conduction.

This problem of frame thickness is also addressed by gas filled windows as generally, gases tend to be more effective in thinner cavities between the panes of glass.

Most manufacturers actually leave a larger gap than necessary to account for potential gas losses in production and throughout the unit’s lifetime once installed.


The effect Argon Filled double glazing has on U values

Average U values of typical glazed units (with 16mm gap) are as follows:

  • U value of single glazing – 5.3
  • U value of air filled double glazing – 2.7
  • U value of Argon filled double glazing – 2.6
  • U value of air filled double glazing with an Low-E (Low Emissivity) coating – 1.8
  • U value of Argon filled double glazing combined with a Low-E coating – 1.6


The Extra costs and potential savings

Estimates suggest that on average Argon filled glazing products are approximately 5% more expensive than their standard air filled counterparts. The potential money that could be saved, of course, depends on the type and size of the property.

House with large double glazed windows and energy rating symbol

Argon filled windows can help your home to reach the required energy rating.

Modern houses with large windows would naturally benefit the most, as they contain a larger surface area from which heat could escape.

Measuring all the windows to be replaced and calculating the savings that could be made in terms of energy loss against conventional air filled windows, gives you a figure to compare against the initial cost of buying the windows.

Given that the savings will repay the increased outlay over a number of years, it is prudent to consider the window’s life expectancy. The generally accepted standard in manufacturing is for double glazed units to achieve a 90% fill of gas.

Approximately 0.5-1% of this gas will evaporate and disperse per year, and because Argon units tend to work efficiently down to 75% volume of gas, they have a lifetime of roughly 20 years.

As a consumer looking at replacement or new windows and doors, it is important to ask whether the extra cost of Argon filled glazing is worth the long term savings for you and your home.


Who offers Argon Filled products?

Due to legislation on energy efficiency and with further regulations expected over the next five years, the vast majority of manufacturers and suppliers offer Argon filled units as part of their range. Many suppliers actually offer Argon filled units as standard.



Argon filled windows currently one the most viable and readily available energy efficient products on the market today.

It enables double glazed windows to be made which meet current WER requirements of C rating (with the correct glass, gap and frame), and therefore should be considered by anyone looking to replace the windows and doors in their home, or buying new double glazed units for any application.

Better performance and less thermal conductivity can reduce the cost of heating significantly over conventional double glazed units. Argon filled products do cost more initially, however, so it is important to assess how much the potential savings could be for your home specifically, before paying the extra initial cost.

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