The History of Energy Efficient Windows

Energy efficient windows are something we take for granted. Whether we’re building a new home or renovating and old one, most of us recognize the environmental and monetary benefits of energy efficient windows.

What is interesting is that the history of energy efficient windows is a so short. In just over 30 years, the US has undergone a revolution in thinking and technology.

What Is The Sound Of A Light Bulb Going On?

In the mid 1970s, the US was confronted with the realization that energy was neither unlimited nor free. Gas lines and wearing sweaters inside became the norm as world politics drove the price of oil to historic highs.

While looking at ways to cut energy use, it became obvious that windows were a key source of heat loss. The US Department of Energy estimated that 25% of home heating costs were devoted to offsetting the effects of heat loss through windows.

At the time, most home windows were single pane windows in wooden frames. Homeowners in colder parts of the country sometimes reduced heat loss with storm windows installed over traditional windows. Replacement windows were typically made with aluminum frames.

Multi-Pane Windows

In the late 1970s, multi-pane windows were an early step forward for energy efficient windows. Taking a cue from storm windows, multi-pane windows use the space between two or more layers of glass as an insulating layer. As multi-pane windows evolved, the space between layers was filled with argon or other inert gasses to improve their insulating properties.

New Framing Materials

As research into energy efficient windows intensified, manufacturers soon learned that aluminum frames were poor insulators and led to significant heat loss. In the 1980s, manufacturers began to produce vinyl and wood-vinyl composite frames. These frames lowered the transfer of heat and again increased the efficiency of windows.

At the same time, manufacturers began to replace the metal spacers that held multi-pane windows apart. The metal spacers were a source of heat loss and they began to be replaced with foam or plastic spacers. These non-metallic spacers were better insulators and reduced heat loss and condensation.

Window Coatings

Toward the end of the 1980s, low-emissivity (low-e) glass began to be incorporated in energy efficient windows. Low-e glass uses a thin layer of metal oxide to create a barrier to infrared radiation. Low-e glass allows visible light to pass through glass, but keeps heat from escaping.

The Future Of Energy Efficient Windows

In the early 2000s, researchers began to develop new coatings that would allow windows to change based on outdoor conditions. Absorbing electrochromic (AE) windows will use a thin layer of material that changes color under a tiny electric current. A light sensor in the window will control the electrical current. AE windows will be transparent during low-light conditions, but will turn darker in sunlight.