Low E-Glass

The ‘E’ in Low E-Glass stands for emissivity. In simple terms, these types of windows have a low rate of heat absorption and emission. In winter, furnaces and heaters keep the room warm, and furniture, upholstery and drapes absorb this heat, but a normal window pane is almost like a big hole letting all the heat escape, as thermal radiation normally moves from warmer to cooler areas. In the case of Low E-Glass the heat just bounces back into the home, leading to minimum energy loss.

By contrast, in summer the same Low E-Glass keeps the heat out. Sunlight consists of visible, ultraviolet (UV) and infrared light (IR). Visible light is what we need but both UV and IR are undesirable. Ultraviolet light damages skin and is the main cause for fabrics fading in a home and the infrared light quickly heats up sidewalks, furniture, floors and even walls. This heat is then emitted by these objects as they cool; this in turn heats up the home. Low E-Glass simply obstructs both the ultraviolet and infrared radiation while allowing visible light in. This results in a much cooler house.

Low E-Glass has been around for some time now and was first introduced in 1979. It was an improvement on insulated windows where two sheets of glass were separated by vacuum or empty air space. So, what is the secret? Low E-Glass is normal glass coated with a microscopic layer of a metal or metal oxide – this could be tin, silver or zinc.

There are two types of Low E-Glass, the hard coat or pyrolytic variety and the soft coat or sputtered kind. In the first case a metal-like tin amalgamates with the slightly molten glass to form a hard, bluish scratch-resistant surface. The latter uses a different technology where a fine spray of silver atoms form a thin coating on the surface of the glass. Although the soft coat Low E-Glass is more efficient and a poorer absorber of heat than the hard coat one, the fragile layer of silver tends to oxidize when exposed to the elements. More often than not soft coat Low E-Glass is sandwiched between two sheets of normal glass and the space in between is filled with argon, which not only protects the silver but also provides further insulation.

Low E-Glass is more expensive, but the benefits outweigh the cost. It not only translates into savings on energy bills but also protects homes from harmful ultraviolet and infrared radiation. It reduces cold spots and makes a home comfortable regardless of the weather outside, and since today’s Low E-Glass is completely color neutral there are no unnatural tints. Best of all, it provides for large windows with minimum energy loss.

The market is flooded with various kinds of Low E-Glass but choosing the right kind that is suitable for the climate in your area is the key. Some types work better in cold climes while others are more efficient in warmer areas. The easiest way to find out which Low E-Glass is the best for you is to look for the R value, which calculates the resistance to heat loss. Of course it is essential to keep up with changes in the market too, as new innovations are popping up all the time. Manufacturers have even gone to the extent of suspending a thin low emissivity film in between two panes, increasing performance further. After all, windows do account for almost 30% of the energy consumed in a home.