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The Engineer: Let’s do a better job on gas fill

Getting your fill

March 19, 2018  By David Heska

As our industry kicks in to gear for another construction season, it’s a good time to look at a few best practices and common failures. First, let’s start with some background before discussing a recent project example.

The use of low-E coatings and inert gas-fills (such as argon or krypton) is widespread among insulating glass unit (IGU) manufacturers seeking improved thermal performance. Research has shown that in double-glazed units low-E coatings can increase the R-value by 50 to 70 per cent and argon fill can increase the R-value by an additional 25 per cent. But here’s an important question: how do we know if this invisible gas has actually been installed in the IGUs?

On one of my recent projects we checked this and what we found out was not good (for either the contractor or the IGU manufacturer).  I’m not here to point fingers and I don’t presume that everyone is guilty because of a couple of bad apples, but I do think that this is something that should be discussed. We all know that the industry-accepted standard argon gas fill level is a minimum of 90 per cent out of the factory. As part of a recent project our team visited the manufacturing plant and completed testing with a spark emission analyzer. The spark emission analyzer is a handheld portable device that is battery operated. A high-voltage spark is launched into the IGU cavity, causing a light to emit, which is then analyzed and a fast reading of the gas concentration is presented within a couple seconds. We were happy to find that most of the IGUs exceeded the 90 per cent fill requirement. However, for one manufacturing run the argon content was between 69 to 74 per cent for small IGUs (approximately one foot by three feet) and between 81 to 86 per cent for large IGUs (approximately four by three feet). The contractor refused to accept these IGUs from the manufacturer and modifications were made to correct this deficiency going forward.  

Of course, insulating glass manufacturers have been aware of these issues for some time and the Insulating Glass Manufacturers Association has been working to correct them. There is even a standing task group within the association – the gas measurement validation group – that sets the standard for verifying gas fill levels. It turns out to be a very complex and scientific problem to solve. Right now it looks like they have argon pretty much licked and the effort is moving on to figure out how to properly calibrate the spark-emission tests to look at other exotic gas fills.  


Another deficiency that we look for when reviewing IGUs are discontinuous primary seals. The polyisobutylene (PIB) primary seal prevents moisture from entering the air/gas space in an IGU. But sometimes there are small gaps in the primary seal (typically at corners) and these gaps allow the inert gas fill out and moisture in. The overall life expectancy of an IGU is greatly reduced if there is a discontinuous primary seal. As a regular part of a typical quality assurance process, manufacturers should be reviewing samples of their product to ensure that the gas fill requirements are met and that primary seals are continuous. Proper workmanship is critical when manufacturing IGUs and the glass needs to be clean and dry for sealants to adhere. It is also important that corner keys are crimped without any gaps and that the plugs/ports are tight.

So whatever your role on projects this summer, whether its leading the manufacturing process, a contractor installing windows, or as an engineer specifying and reviewing work on site, let’s all keep these two items in mind. Let’s do our part to discard the IGUs with discontinuous primary seals and inadequate gas fill and let’s keep our heads held high knowing we’re in this together. •

David Heska, P.Eng. is a director with WSP’s Building Sciences team in southwestern Ontario. He oversees the operation of the Hamilton, Kitchener and Windsor offices. David has been involved on window simulation projects as well as the design and replacement of windows in commercial and residential buildings. He can be reached at

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