Energy Efficient Windows

This post was written by me but originally appeared at

The first window was made about 3.3 million years ago and was a hole in the wall of whatever was being used for shelter at the time. The purpose was to better see enemies and wild animals approaching as well as to enjoy a cool breeze on a hot summer night.

The Romans were the first known to use glass for windows, a technology likely first produced in Roman Egypt—In Alexandria ca. 100 AD. The technology has advanced significantly over the years although some people still use Jalousie windows which are only slightly better than a hole in the wall.

Untitled-e1430525842626Before deciding on new windows it is important to know a little bit about how the sun’s radiation works. The sun emits a lot of radiation but for the purposes of window efficiency, we can focus of visible light and radiant energy (heat). The goal, in both hot and cold climes, is to allow as much visible light through while minimizing the transference of radiant energy. There are three main ways to treat glass to make it energy efficient. These are insulated glass, low e glass, and reflective coated glass.

Insulated glass windows usually consist of two or three panes of glass separated by an inert nonconductive gas like Argon. The spacers often have a desiccant, which reduces the possibility of moisture entry.

Low emissivity glass has been coated with a microscopic metallic oxide that reflects infrared light (radiant energy) and allows visible light through. Low E coatings come in different varieties which can be customized to fit a specific location, cold and dark vs hot and light.

Public Toilet with reflecting glass

Reflective coatings are usually used in hot areas with windows getting direct sunlight. For example the front of our hardware store has very large south facing windows so we put a reflective coating on them so we wouldn’t have to use exorbitant amounts of air conditioning. Some of the more severe reflecting coatings will turn glass into a one way mirror.

The type of frame for a window is also important for durability and energy efficiency. Aluminum windows are durable and cheap but have a high heat conductivity which is bad for energy efficiency. Wood window frames look nice and have good insulating properties but require more maintenance because wood tends to warp with heat and moisture. Fiberglass frames provide good insulation and generally look better than aluminum. Fiberglass is also very strong and can accommodate a larger piece of glass. Vinyl frames are the most energy efficient, require no maintenance and can be custom treated for any environment.

Our atmosphere and magnetic field protects us from most of the Sun’s harmful radiation and we as technologically advanced animals can further protect ourselves from other inconveniences like heat and high electric bills.

%d bloggers like this: