The Importance Of Warm Edge Spacer Technology Explained

by Frank Giuseppini

As you do your research on the product portion of your replacement window and patio door project, you have probably read or heard some window retailers state that the window and patio door products they are quoting utilize a “Warm Edge Spacer.”  So why is that important?  Well, let’s explore what warm edge spacers are, and the answer to that question will be clear. 

Windows, defined as openings that allow the passage of light (and sometimes air) into a structure, have been around for about 3500 years. For the vast majority of that time, windows were just openings sometimes covered with retractable wood, paper or cloth.  When I was a kid I always amused by how Dino the dinosaur used to stick his head into the Flintstone’s house and interact with Fred and Wilma (and later Pebbles). There were no window frames sashes or glass. True to the period “cave motif.”

 It was the Romans, after conquering Egypt (after all, sand is the major ingredient in glass!), that came up with a way of using glass for windows. Still for almost 2000 more years the vast majority of windows remained just openings in buildings with coverings until the mid 17th century, when glass production and glazing methods became more practical.  Initially this glass glazing served three purposes.  First to continue to let in light through the opening. Second to keep some of the weather outdoors. And third, to keep (Dino the pet dinosaur) critters and pests outside the building, or buzzing in and out at their will.  It wasn’t until a couple of hundred years later that the “window industry” driven by the concerns of the consumer, became interested in a fourth purpose. Energy efficiency. 

Enter “insulated glazing” or what is referred to as the “integrated glass unit” (IGU).

The layers of glazing in an insulating unit must be held apart at the appropriate distance by an air tight gasket like system we call a “spacer.” Because of its excellent structural properties, window manufacturers started using aluminum or steel spacers in the 1960’s and 1970’s. Unfortunately, metals such as aluminum or steel are an excellent conductor of heat and the aluminum spacer used in most standard edge systems represented a significant thermal “short circuit” at the edge of the IGU, which reduces the benefits of improved glazings. In addition to the increased heat loss, the colder edge is more prone to condensation and because of its rigidity metal spacers have a lower resistance to the expansion and contraction forces in the IGU thus the window or patio door will have less resistance to stress cracks or seal failure in the IGU.  Aluminum spacers and spacers that utilize a significant amount of metal in their configuration (quasi warm edge) are still used in many windows and patio doors on the market today. 

In the mid 1990’s we at Jantek Windows got to designing and manufacturing windows with new “warm edge” spacer technology. Today, all of the windows and patio doors we manufacture utilize the absolute latest warm edge spacer technology as one of the core components of our proprietary  EnergyMiser II™ IGU technology. This reduces thermal conductivity while improving surface and corner appearance over other insulating glass spacers. Our innovative EnergyMiser II IGU, with warm edge spacer system saves energy by insulating the frame and edge of the insulated glass unit making the unit much less conductive around the perimeter of the glass.

Warm Edge Spacer low heat conductivity

Warm Edge Spacers                                                    Warm edge spacers use a layered buildup or composite of materials have low heat conductivity and reflect heat in during cold weather and out during hot weather. Some are flexible and reduce risk of seal failure and glass stress cracks

Aluminum spacer has high heat conductiivity

Aluminum spacers have high heat conductivity allowing more heat to escape in cold weather and more heat to enter in hot weather. Also the inflexibility of metal contributes to higher risk of seal failure and stress related glass cracks


Warm edge spacers have become increasingly important as manufacturers switch from conventional double glazing to higher-performance glazing in high performance windows such as we produce here at Jantek Windows. For purposes of determining the overall window U-factor, the type of edge spacer has an effect that extends beyond the physical size of the spacer to a band about 2-1/2 inches (64 mm) wide. The contribution of this 2-1/2-inch-wide “glass edge” to the total window U-factor depends on the size of the window. Glass edge effects are more important for smaller windows, which have a proportionately larger glass edge area. For a typical residential-size window (3 by 4 feet/0.8 by 1.2 meters), changing from a standard aluminum edge to a good-quality warm edge will reduce the overall window U- factor by approximately .02 Btu/hr-sq ft-°F.

Another significant benefit may be the rise in interior surface temperature at the bottom edge of the window, which is most subject to condensation. With an outside temperature of 0°F, a thermally improved spacer could result in temperature increases of 6-8°F (3-4°C) at the window sightline–or 4-6°F (2-4°C) at a point one inch in from the sightline, which is an important improvement.

As new highly insulating multiple layer (like Jantek’s triple pane R5 EnergyMiser II™) glass windows are developed, the improved edge spacer becomes an even more important.  As a designer and manufacture we at Jantek Windows are constantly vigilant to ensure we are “pushing the envelope” on energy and comfort performance of our windows and patio doors. 

Remember that the type of spacer used in your windows and patio doors, though very important, is only one of the components of design that factor into the overall energy and comfort performance of the window or patio door.  So, if the energy and comfort performance of your replacement windows and patio doors is important to you, then you need to understand how to compare this important criteria between the different window and patio door proposals that you are receiving for your project.  I strongly suggest that you read the article on how to compare the Energy and comfort performance of window and patio door brands that I wrote awhile back. 

Well, I hope this article has helped you with a better understanding of the important role that the spacer system plays in the overall energy and comfort performance of the window and patio doors that you are considering for your replacement window project.

If you have any questions, we at Jantek are experts in the design, manufacturing, and installation of replacement windows and patio doors.  We are intent on assisting you in making the best choice of the contractor and the product for you no matter whom that may be if not us.

Want to know how much your replacement window and patio door project will cost? Get a free no hassle TeleEstimate right now! 

Until next time… “Save energy, be comfortable!”

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