Double Glazing - Gas Filling

Double glazing without low-e coating uses air between the panes as insulation. As air itself is a good insulator, filling the gap between the glass panes with a low-conductivity gas such as argon reduces conductive and convective heat transfers. This is because the density of the gas is greater than the density of the air.

Argon is the most commonly used gas, due to its excellent thermal performance and cost-efficiency in comparison to other gases. Argon gas reduces heat loss in double glazing by slowing down convection inside the air space. It is extremely cost-efficient, and works well with Low-e coated glazing. Argon and Krypton are colourless, odourless, non-flammable and non-reactive inert gases.

It is generally accepted that the double glazed unit should achieve a 90% fill gas concentration. Over time this concentration will gradually evaporate, at an estimated rate of 0.5 to 1% per year. Double glazed units filled with argon do not degrade significantly until they reach 75% concentration, giving up to 20 years of high performance.

Argon gas is quite inexpensive and quickly produces cost-savings to justify the cost.

Krypton is more effective at reducing heat loss, but is roughly 200 times more expensive than argon per unit volume. Because Krypton works best at smaller pane spacings (8 mm), it is often used in triple and quadruple-glazed windows to minimize the overall thickness of the unit.

Other types of gases can be used (for example, sulphur hexafluoride, carbon dioxide) to reduce sound transmission, but these gases do not offer the improved thermal performance of the inert gases mentioned above.

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Double Glazing - Gas Filling

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