What is an Insulated Glass Unit (IGU)?

Windows are more than just holes in your walls to let light in. They help keep your home cool in the summer and warm in the winter, reduce noise from outside, and help circulate air flow while managing condensation – if they’re built right. One of the most important parts of a modern window system is something you might not realize is there: the insulated glass unit, or IGU for short.

By understanding what an IGU is (and what it isn’t), you can make smarter decisions as a homeowner when it comes to replacing a fogged-up or broken window or planning a new installation. This handy primer will go deeper on what an IGU is, how they work, how they compare to single-pane windows, and how to identify potential problems that signal a need for replacement.

What is an IGU?

As the name implies, an insulated glass unit is a sealed window component made up of two or more panes of glass that are separated by space filled with air or a gas such as argon or krypton. These panes are then held together by a spacer and sealed to form a single unit that fits into the window frame.

Because of their thermal insulation properties, IGUs are often used for exterior windows to reduce heat transfer between the inside and outside of your home. You might also know IGUs by a different name: either double- or triple-pane windows (depending on the number of panes), double- or triple-glazed windows, or simply “thermopanes.”

How Do IGUs Work?

IGUs have four main parts that work together to regulate temperature, reduce noise, and keep you comfortable no matter the season:

• Glass layers: two or more panes provide a physical barrier against temperature shifts.

• Gas: the space between the panes is filled with air or an inert gas like argon or krypton. While good ol’ plain air can be a helpful buffer, argon and krypton are denser gases, slowing down heat transfer further and even providing enhanced noise insulation.

• Sealed edges: seals keep the gas in between the panes and keep moisture out, preventing condensation and fogging within the spacers.

• Low-E coatings: some IGUs have specialized coatings that reflect heat and UV rays, keeping your home cooler in the summer and warmer in the winter.

A note on gas fill: the choice between air, argon, and krypton may be an important decision, especially when it comes to insulation, noise reduction, and the width of the IGU’s spacers. While krypton has roughly the same performance as argon, krypton can be used in thinner IGUs and is often used in triple-pane units. However, this results in a much more expensive unit. 

With that in mind, if you’re looking for a good middle ground between cost and performance, argon-filled double-pane IGUs are a solid option.

IGUs vs. Single-Pane Glass

Unless you live in a very old home, there’s a good chance all of your windows are IGUs anyway. However, single-pane windows can still be found in exterior-facing frames which, depending on how they’re used, can affect cost and comfort.

For instance, because a single-pane window, by definition, has only one pane, the only insulating factor for heat and noise reduction is the glass itself (which glass, as a material, doesn’t do that great of a job on its own). Because of this, indoor temperatures can vary throughout the day and from season to season with a high risk of condensation, especially if you live in humid climates.

While this might not be important if the single-pane windows are used as interior glass (such as shower panes or office dividers) or as exterior windows for sheds, workshops, garages, and other out-buildings, it might be worth considering replacing them with IGUs to keep climate-controlled spaces more comfortable and energy-efficient.

Common IGU Problems (and When to Replace Them)

While IGUs are built to last typically between 10 to 20 years, they can still potentially fail before then. Seals are especially prone to problems due to sudden weather changes, improper installation, or faulty mixing. Some signs that your IGU may need replacement include:

• Fogging and condensation stuck between panes (this happens as the internal gases slowly leak out and are replaced with moist air from outside).

• Cracks, chips, or other damage to the glass.

• Drafts or whistling coming from what should be a sealed window.

• Noticeable rise in heating or cooling bills as well as a noticeable change in temperature around the window (you can feel the hot or cold air from outside radiating intensely).

Though IGUs are self-contained and can fit into window frames with relative ease, you might not want to spend the time, energy, and stress trying to fix these problems. At Glasscadia, we specialize in replacing damaged or failed IGUs. Whether you’re dealing with a foggy window or planning a whole renovation project, we’ll make sure your replacement matches the original quality and performance or help you find the right alternative to fit your budget and needs.

Luckily, not every foggy or underperforming window needs a full replacement. Get in touch with us today and we’ll be happy to inspect your windows and determine if an IGU replacement is the right solution. Our helpful experts are happy to keep your money from flying out the window.