Money may not grow on trees, but it can practically fly out windows if you’re not careful. No one wants to spend more money than they have to keeping an interior space’s temperature comfortable, whether that’s for cooling it in hot weather, or heating it in the cold.
That’s where low-e -- or low-emissivity -- glass shines, especially as part of insulated glass units (IGUs).
Pairing the performance of standard glass sheets with energy efficiency, IGUs made with low-e glass are designed to be a barrier against solar heat and heat loss.
With enhanced insulating properties against the elements, low-e insulated glass units reduce energy costs in summer by decreasing the solar heat gain coefficient (SHGC) – the amount of solar radiation entering a space through glass and released inside as heat. And in the winter, low-e coatings reflect internal heat back inside, reducing heat loss.
While low-e windows cost more than regular windows, they reduce energy loss by as much as 30% to 50%. Combine that with insulating features, whether double- or triple-pane, and you’re talking about significant savings.
How Are Low-E IGUs Manufactured?
Low-e windows are made by first applying one or more ultra-thin coatings to a pane of glass. Each coating consists of a metal element that reflects ultraviolet rays and heat, as well as an outer layer that improves durability.
In creating an IGU with low-e insulation, a narrow strip of coating around the perimeter of a pane’s edge is removed. This allows sealants to directly bond to a piece of glass and prevents coating corrosion.
To maximize efficiency and increase insulation, the space between the panes is filled with an inert gas and sealed. Common inert gasses in IGUs include:
Argon is used most often, as it’s the most affordable.
What Types of Low-E Glass Are Available for IGUs?
There are two types of low-e coatings used in IGUs: pyrolytic hard coat and soft coat. Both have their strengths and weaknesses in creating energy-efficient windows.
Pyrolytic Hard Coat
During manufacturing, while a glass pane is still slightly molten, a single, thin layer of molten metal low-e coating is applied. As the coating and glass cool, they fuse together to form a strong, “hard coat” bond.
This process makes the hard coat more durable, but slightly less energy efficient. That’s why pyrolytic hard coat is often used for exterior windows in environments where harsh weather and strong winds are common.
Magnetron Sputter Vacuum Deposition
A more energy efficient solution, Magnetron Sputter Vacuum Deposition (MSVD), also known as soft coat, requires a bit more skill during manufacturing.
Once a glass pane is cooled and washed, several low-e coatings are applied at room temperature in a vacuum-sealed environment to its surfaces immediately before going into an IGU. With its additional layers of coating, soft coat offers more protection from UV rays and solar heat gain. However, it is also more delicate, thus “soft,” and not as well suited for harsher climates.
Some of the highest-performing soft coat low-e glass is made with a double or triple layer of silver. Of note, silver is especially challenging to work with and must be handled by an experienced and certified professional.
Beyond the IGU: Low-E Glass Applications
Anywhere energy efficiency is a must, low-e glass is practical. In some cases, state and/or local codes require it.
Even when not required, low-e glass is still helpful because it reduces drafts, lowers utility bills, and blocks harmful UV rays, while, letting in plenty of visible light. It’s an excellent choice for:
- Glass doors
- Glass walls
Low-e IGUs: An Investment in Savings
Regardless of climate, low-e IGUs help maintain a consistent temperature in just about any space, reducing heat transfer through solar heat gain coefficient and heat loss, keeping both the cold and heat where they belong.
Your thermostat can remain relatively untouched, no matter the season.
Interested in using low-e glass IGUs to reduce energy loss?
Learn more about our insulated glass unit manufacturing capabilities:
(Editor's note: This article was originally published in October 2020 and was recently updated).