A Brief History of Window Glass

As you do your research on the product portion of your replacement window and patio door project, it is important that you understand the evolution of the technology over time and the driving forces behind its development. For example, 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, what is that and why is it important? Well, let’s explore the evolution of windows, including things like warm edge spacers and you will have more information to make your replacement window decisions.

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. There were no window frames sashes or glass.

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 airtight 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 standard windows represented a significant thermal “short circuit” at the edge of the Insulated Glass Unit (IGU), which reduces the benefits of improved glazing. In addition to the increased heat loss, the colder edge is more prone to condensation and because of its rigidity metal spacers in windows 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 began designing and manufacturing windows with “warm edge” glass spacer technology. Today, all of the windows and patio doors we manufacture utilize the absolute latest spacer technology as one of the core components of our proprietary EnergyMiser TechnologyÔ. This reduces thermal conductivity over other insulating glass spacers. Our innovative EnergyMiser glass unit utilizes triple pane Low-E coated glass, DuraSeal Warm Edge Spacer, and Argon gas fill.  The design 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 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 window seal failure and glass stress cracks.

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 window manufacturers switch from conventional double glazing to high-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 a sizable effect. For a typical residential-size window changing from a standard aluminum edge to a good-quality warm edge will reduce the overall window U- factor and increase insulation value by about 10%.

As new highly insulating multiple layer (like Jantek’s triple pane windows) 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.

To understand all of the other important criteria regarding windows and energy efficiency checkout the videos here https://jantekwindows.com/category/energy-performance/