What Are Insulated Glass Windows?

What Are Insulated Glass Windows?

Your windows are foggy at various points in the day. Sometimes you feel a chill when you walk past. A few even rattle. They’re almost impossible to open and close. Not to mention, your energy costs are through the roof month after month.

These are all signs it's time for new windows.

But don’t slap any windows onto your home. This is a serious investment!            

We at Brennan have provided over 40 years of new and replacement window services. That's more than just offering home improvement services. That's 40 years of helping people understand the unique needs of their homes and how to meet them. 

Today, we want to share what we know about Insulated Glass Windows, or as we refer to them in the window industry– Insulated Glass Units (IGUs). 

Double pane glass black windows installed by Brennan


Before we get into the nuts and bolts of this article, let’s define some terms and abbreviations you’ll see regarding these window types:

Insulated Glass Unit (IGU) -  A window system including multiple glass panes and gas fixed in a frame.

Glass - Sheet glass made suitable for windows. Available in a variety of thermal or chemical treatments including coatings, laminations, and as tempered (to increase strength).   

Glaze - Often used interchangeably with glass. Can also refer to putty used as a weathertight sealant between the glass and frame.

Gas - Usually Argon or Krypton gas added between the panes of glass in a window unit for added thermal efficiency. Both are colorless, odorless, and non-toxic.

Spacer Bar - Separates the glass to the appropriate distance and absorbs stress caused by thermal expansion. Usually metal. Provides a tight seal to hold in gas and acts as a moisture barrier. May also include desiccant to further discourage moisture.

Double Pane - Two layers of glass per window sash.

Triple Pane - Three layers of glass per window sash.

Solar Heat Gain Coefficient (SHGC) - Measures a window’s ability to block heat producing solar rays on a scale of 0 to 1. The lower the rating, the less solar heat the window transmits. In other words, the lower the rating the better the window is at blocking solar radiation.

U-Factor - Also referred to as U-Value. Measures a window’s ability to reduce heat and cold transfer on a scale of .20 to 1.20. A lower rating indicates better resistance to thermal heat flow and greater insulating properties.  

Double pane windows installed by Brennan

Anatomy of Insulated Glass Units

An Insulated Glass Unit (IGU) combines many panes of glass into one window system. The multiple panes of glass and gas add extra barriers to heat and cold transfer.

It used to be standard to fix one pane of glass into a frame to make a window. The only barrier between your home and the outside environment was a single sheet of glass. We now know that’s one of the least effective ways to construct a window if you want them to provide good insulation. In fact, when researching windows, you may find that it’s harder to find single pane units. They’re there, but most window companies do not default to this option.

Double Pane IGUs

This is a window system with two glass panes separated by gas. In the world of residential IGUs, these are the most common. 

Insulated glass units include double pane windows filled with argon or krypton gas for increased insulation.

Triple Pane IGUs

This is a window unit that containing three panes of glass. There’s an interior pane, an exterior pane, and a pane between those two. Gas is filled into the spaces between interior and exterior panes.

Insulated glass units include triple pane windows filled with argon or krypton gas for increased insulation.

Benefits of Insulated Glass Units

Insulated Glass Units beef up the barrier between your home and the outdoors. 

Extra layers of glass along with dense gas help to resist heat and cold transfer. The units also curb heat producing solar rays. So, a west facing IGU with extended sun exposure won't heat up as much as a single pane unit. Your heating and cooling system won’t need to work as hard to maintain your comfort.

Several formulas help to determine a window's energy efficiency. One of them is the Solar Heat Gain Coefficient (SHGC). It measures a window's ability to reduce heat created from solar rays. Another is the U-factor which measures heat and cold transfer. Energy Star's SHGC ratings outline energy efficiency in all four US climate zones:

Insulated glass units like double pane or triple pane windows can help home insulation across many US regions



Insulated glass units like double pane and triple pane windows typically have insulation properties meeting or exceeding Energy Star standards.

Energy Star certified windows in North Texas needs to have both an SHGC of 0.25 or less and a U-factor 0.30 or less.

Looking for replacement windows in North Texas? Consider these Energy Star approved window lines for the South Central region. Brennan offers many lines to choose from. Here are just a few:

Considerations for Insulated Glass Units

Proper installation of a window has a significant impact on how it performs. Insulated Glass Units are no different. Improper sealing of IGUs can lead to a number of issues. This includes fog and escaped gas. The gas used in Insulated Glass Units is an option of either Argon or Krypton. These gases are non-toxic in the quantities found in IGUs. However, a large portion of the insulation power lies with these gases. You don’t want it escaping and reducing the value of the unit. This can happen with seal failure. The best way to avoid leaks is with quality, professional installation.

Insulated glass units if installed improperly can lose their insulation properties. Brennan Enterprises offers 40 years of professional window installation.

If you want to really reap the energy saving benefits of IGUs, installing just one in your home probably won’t do it. You’ll need to replace many of your old windows at the same time. This leads to our next consideration: pricing.

How much do insulated glass windows cost?

IGUs contain extra materials versus traditional single pane glass. It makes sense that double and triple pane window units are priced higher.

As a case study, we'll look at a Brennan Traditions window. This pricing is for a standard size window unit without the cost of installation:

Single hung window in white with a high-performance double pane unit: $545.
Single hung window in white with a high-performance triple pane unit: $622.

Consider you replaced five single pane units with the above double pane option. The ROI for these windows would be about 10 years based on average ENERGY STAR cost savings for North Texas. Of course, home improvements add to the value of a house. Insulated Glass Units, with their energy-saving properties, can help increase the resell value of your home.

Insulated glass units like double pane windows and triple pane windows help to better insulate homes and can add to house resell value.


Insulated Glass Units are a great option for a more energy efficient home. Extra glass and gas add extra protection against the elements. Less heat/cold transfer means less reliance on your HVAC system for temperature regulation. That’s more money in your pocket. 

Brennan has a team of experienced consultants and window installers eager to help increase your home’s energy efficiency. Are you ready to dive in and get personalized advice?

Call us today at 817-856-2480 to set up a consultation! 

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