How is a double glazed window made?

12 Jul

With all this talk of double glazing and its benefits,  a thought sprung to mind. How many of us actually know what goes in to making a double glazed window? Ok we know some of you are now saying, yes that’s easy, but for those shaking their heads and thinking that’s an interesting question, here goes!

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Let’s start with a little history. The double glazed window was invented way back in the 1930s, and was commonly available in America in the 1950s under the Thermopane brand name, and registered in 1941 by Libbey-Owens-Ford Glass Company. Now many decades later, the manufacturing process is well established.

A double glazing window comprises two panes of glass, separated by a spacer bar and seals, to create a hermetically-sealed environment. An adhesive sealant is applied to the face of the spacer on each side and the panes pressed against the spacer.The cavity is filled under vacuum conditions with either air or an inert (unreactive) gas like argon to improve insulation and prevent condensation within the unit. As the air or inert gas are poor conductors of heat, there is a great insulation effect. The filled gap between the two sheets of glass reduces the heat conduction between the panes, keeping the warm air in and the cold air out! This makes the home more energy efficient and reduces the bills. Great news for us !

If the double glazed unit is gas filled, two holes are drilled into the spacer of the assembled unit, lines are attached to draw out the air out of the space and replacing it with the desired gas. The lines are then removed and holes sealed to contain the gas. The more modern technique is to use an online gas filler, which eliminates the need to drill holes in the spacer. The units are then sealed on the edge side using either polysulphide or silicone sealant to prevent humid outside air from entering the unit. This will make sure that no condensation of the glass panes facing the air space during cold weather will occur.

The humble double glazed window has come a long way, from the original double glazed sealed units of two sheets of float glass with a very small spacer bar, to today’s high specification and more energy efficient double glazed sealed units, with toughened safety glass, wide spacer bars and sometimes a film on the glass which allows the double glazed unit to clean itself.  Who could ask for more ?!

Well there you have it in a nutshell. We could keep going with more information on thermal performance,  heat insulating properties,  acoustic insulating properties, longevity,  estimating heat loss from double glazed windows, etc, but we will keep that for another time!



5 Responses to “How is a double glazed window made?”

  1. americanexteriorsllc September 25, 2012 at 4:53 pm #

    Most double glazed windows in the industry are considered energy efficient due to the gas that is filled between the panes. One of the biggest factors to consider is the type of spacer system that is used. The spacer system is what will maintain the high performance of the double glazed window.

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  1. The Evolution of the Window « blogging - November 30, 2012

    […] If you would like to know a double glazed window is made, just take a look at our previous blog […]

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