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Posted by on Sep 13, 2016 in Uncategorized |

A Brief Look At Low-E Glass

Your choice of replacement windows can not only affect the look of your home, but it can also have an impact on your home’s overall energy efficiency. Low-E glass is specifically designed to reflect excess heat and light, keeping your home cooler throughout the day while helping you save money on heating and cooling costs. The following takes a look at this recent technological innovation and how it can benefit your home.

What Is Low-E?

The term “Low-E” is simply shorthand for “low emissivity,” reflecting its ability to allow only low levels of radiant energy to pass through. Ordinary window glass has high thermal emissivity, meaning that just about all of the energy given off by the sun passes through unimpeded. With clear windows, your home is absorbing all of that radiant energy during the daylight hours. At night, the opposite occurs — all of the radiant energy stored in your home escapes out of the windows. This explains why certain rooms in your house can seem unbearably hot during the daytime, only to become freezing cold at night.

Highly emissive glass can be made to transmit less radiant energy simply by adding a thin metallic coating to the surface. A Low-E window uses this type of coating to regulate the radiant energy that’d normally pass through a clear window. The film reduces light transmission by a very small amount, but more importantly, it also blocks infrared energy from coming through. The end result is a window that manages to keep excess heat out during the day while holding it in your home during the night.  

Hard Coat vs. Soft Coat

The metallic coating used with Low-E glass can be a hard coat or a soft coat. A hard coat, also known as a pyrolytic coat, is applied during the production process. The tin dioxide coating fuses to the hot glass surface, usually taking on a bluish tint in the process. The end result is a hardened coating that resists wear and most forms of damage. Hard coatings are preferable for cold climates, since the coating is emissive enough to allow some infrared energy through and keep the building warm during the winter months.

A soft coat is applied after the glass has been cut. The cut sheets are placed into a vacuum chamber and bombarded with layers of silver via magnetron sputtering. After several thin layers have been applied to the glass, the glass is sandwiched together with the Low-E coating on the interior of the panes. Soft coat Low-E coatings require more protection, as these are usually more fragile than hard coats. However, soft coats offer drastically reduce UV transmittance and offer a lower U-value than their hard coat counterparts. This makes Low-E soft coatings a better choice for sunnier climates.