Blog > Category > Posted: 2022-Jun-28, Updated: 2023-May-03

Not all windows are full of hot air

Gas between the glass - Windows
Modern windows are not just openings in our walls anymore. They have become a crucial component of our home's energy efficiency and comfort. Selecting the right gas for your windows can make a significant difference in your home's ambience, energy consumption, and budget.

Does it really matter?

Yes, it does -The right gas can help maintain a consistent temperature inside your home, reduce energy consumption, and improve insulating properties. It's crucial to consult with a professional to determine the best gas for your windows and to ensure that they are installed correctly.

The history

Multi-paned (multi-glazed) windows are made up of two or more glass panes that when bonded together and filled with gas form a single-window system IGU's (insulated glass units. Invented in Scotland during the Victorian age, the original double-paned windows were naturally filled with air. Today, through sophisticated manufacturing technologies, the space between the windows is filled with various types of gasses that make the IGUs better in so many ways.

In the early 1970s, in an attempt at getting soring energy costs down, Window companies began to experiment with noble gasses theorizing that because they were denser than air, would increase the insulation value of a window.

Going green

In today’s ever-changing technology world, homeowners are becoming more energy cost-conscious and at the same time have fallen victim to a trend of opening up their homes to more natural light (for most houses the windows are the weakest insulated spot of all). For many homeowners, the benefits of improved outdoor views and better lighting and openness outweigh the potential energy loss. A bit of a concern, considering that windows currently only achieve, at their highest, an R-value of about 4 compared to solid walls, which rate somewhere between an R-value of 30 to 40.

How does gas work

Gas in glass acts as an insulator, working in both summer and winter to keep interiors protected from outside temperatures. The denser the air space between the glass, the better the insulation properties. To increase the insulation of a window, inert (noble) gasses are used to fill the spaces between glass panes. Window makers regularly use argon, krypton, and xenon to turn ordinary glazing into draft-defying superglass. In addition to improving the comfort of your home, insulated windows have several other benefits, they lessen noise pollution and limit damaging ultraviolet rays from entering the interior of the home.

  • The density of air is 1.2922 g/L
  • The density of argon is 1.784 g/L
  • The density of krypton is 3.749 g/L
  • The density of xenon is 5.894 g/L

Is this gas harmful?

The gases used to fill window IGUs (argon, krypton and xenon) are inert (non-reactive) and occur naturally in the Earth’s atmosphere. Argon, the most common, comprises about 2% of the air we breathe. Both Krypton and xenon are very rare and need to be extracted from the air before they can be used in window manufacturing. The three gasses have soundproofing ability when compared to air fills.


Argon, which comprises slightly less than 1% of the Earth’s atmosphere, is non-toxic, inert, clear and odourless. It is the industry standard for filling double-glazed IGUs because of its ratio of cost (it’s inexpensive) to energy efficiency. Argon offers a thermal conductivity around a third lower than ordinary air, for only a marginal increase in cost. It does an excellent job of diverting heat gain during summer while keeping the interior nice and cosy during winter. IGUs filled with argon are also less prone to clouding (interior condensation) because argon has less moisture in it than air.


Krypton is more than twice as dense as argon and it’s often considered the standard for triple-paned IGUs where the total glazing unit thickness must be minimized i.e. spacing between the glass is 1/4” to 3/8” (6mm to 9mm). If krypton is used in a wider than 20mm gap, convection currents will begin to form resulting in the transfer of heat from the interior of the window to the exterior. Krypton is one of the rarest gases in the Earth’s atmosphere, it makes up just 1 part per million by volume and is extracted through the distillation of air that has been cooled until it is a liquid. Krypton is currently about 100x more expensive than argon. Although krypton-insulated windows demonstrate superior energy performance and can significantly reduce monthly energy expenses, the higher cost has made it prohibitive for many homeowners.


Xenon insulation represents cutting-edge window insulation technology and will usually cost significantly more than both argon or krypton, with just slightly better energy savings in return. Xenon is very rarely used in residential homes because the costs far exceed potential energy cost savings. A relatively recent innovation, Xenon-filled IGUs sit at the forefront of glazing technology and probably are not worth considering unless you are thinking of building a home and you’d like to incorporate a lot of glass.

Even better results

Window manufacturers often combine gasses with low-emissivity (low-E) coating to the glass panes to keep the interior pane of glass closer to the temperatures of the interior air, minimizing air currents that are created when different temperatures come into contact.

What about leaks?

Gas-filled windows will leak over time, as much as 1% per year, according to some estimates. It all depends on the quality of the window, its installation, the climate and exposure to the sun… However, even after 20 years, a slow-leaking window will still perform well with an 80% gas fill. Reputable window manufacturers will certify their products to ensure they won’t leak (In Canada, the AAMA certification label indicates that a sample of the product has been verified as conforming to the standards of Certified Products Directory (CPD), the industry’s preeminent resource for window and door products.

How do you know when an IGU is running out of gas?

Condensation or fog (you may also see white residue) inside the window unit indicates that the gas fill has escaped and been replaced with moisture-laden air. Leaked argon, krypton and xenon pose no health hazards to a home’s occupants.

What should I look for when buying gas-filled windows?

If you want the best bang for your buck, be sure to ask your window company for warranty details on the gas-filled IGUs. A company that warrants the units for life (25 years) with no installation charges to replace failing IGUs indicate a quality no-hassle product.

Related topics

Infographic - What’s to know about window glass

What is Low-E Glass?

Infographic - The Protective Properties of Window Glass

Window Spacers - What's the difference?

Windows, you've got options

Getting the best window product, value and price

Need more information?

Understanding the benefits of different gas fills for windows is crucial for maximizing energy efficiency. Unfortunately, this information is often overlooked. Contact us for more information on the gas fills used in our products. Our team is always happy to answer any questions you may have and help you make the best decision for your home.

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