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Extend the life of your windows & save energy

Glazing sealed unit properties: ways to improve a window without changing the whole thing.

Tips on extending the lifetime of your windows and reducing their energy consumption by Simon Rolland, owner of Basco Calgary, Alberta.

Windows are a key feature of every building. They contribute to our comfort by allowing natural light inside, while having the ability to maintain our privacy (textured, tinted, or reflective). Not only can a sealed unit impact the look and privacy of a building, it can also significantly impact the acoustics and the amount of heat that is radiating in or out.


It is possible to reduce the Outdoor-Indoor Transmission of noise (OITC) by only changing the glazing sealed unit of a window (without changing the frame) by considering the following factors: use different glass thickness, increased airspace between panes, and use of laminated glass. In a double pane sealed unit, selecting one pane of glass with a thickness of 3mm, and another with 4mm will reduce noise transmission since each pane will react differently to each frequency, and part of the “harmony” will be lost. While playing with the thickness of the glass helps, increasing the airspace (when possible) will lead to better results, especially when combined with laminated glass.

Without getting into complex calculations, a noise reduction of 28 decibels can be achieved by using a basic 1/8” + 1/8” panes with 1/4” airspace, while changing to a sealed unit with ¼” + ¼” panes with 1” airspace will reach 37 decibels. It is possible to reach levels in the high 40s of decibel reduction by combining a right mix of laminated glass with different thickness and an increased airspace.


Although exposure to UV light is a primary contributor to home furnishings fading, experts now agree that shorter wavelengths (such as UV light) are responsible for 60% of the damage, whereas longer wavelengths (such as visible light and infrared light) account for 40% of it. When changing or upgrading a sealed unit, selecting the right coating applied on the glass can drastically reduce the impact of such damage over time (a “Solarban 70” type of Low-E is proven to reduce interior fading by 43% when compared to a clear/clear double glazed unit).


Similarly, it is possible to choose a sealed unit that will either reduce or increase the amount of heat coming through a window. This is accomplished by using a low-emissivity (that’s what Low-E actually stands for) coating on a glass unit (usually microscopic silver particles). To properly understand this principle, it is helpful to explain how sun wave energy is transmitted.

Short wave energy is energy that emanates directly from the sun in the form of sunlight. Long wave energy is not derived directly by the sun – it is re radiated off other surfaces. The ability of a material to radiate energy (known as emissivity) if one important way heat transfer occurs with windows. Coating one surface of one of the glass panes can reduce such heat radiation by blocking a portion of the UV and infrared light, while allowing a high percentage of visible light to come through (meaning reduction in artificial lighting need, reduction long wave heat gain/loss, and overall reduction in energy usage).

Another feature of a sealed unit that impacts its heat transfer properties, but is frequently omitted is its actual construction. Using a clear/clear/clear triple glazed unit with Low-E can achieve a U-Value (measure of the heat loss that a surface allows; the lower the number, the less heat loss) of 0.05, while a typical clear/clear double glazed unit will reach a U-Value of 0.74. Not to be neglected, the spacer is the material that runs along the interior periphery of the sealed unit and seals the two (or three) panes of glass together. There are a few types of spacers on the market, fabricated with aluminium, stainless, or structural foam (“warm edge”). It is generally acknowledged that the non-metallic type of spacer contributes to reduce heat transfer when compared to the metal ones.

Finally, the airspace between the Sealed Unit panes play a role as well, although less impactful. A thicker airspace will provide a better insulation, and the use of argon gas to fill the airspace will further increase the insulation. Most Low-E Sealed Units are sold with argon filled airspace.

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