Clera Windows + Doors Blog

What is Low-E Glass?

Thanks to its high versatility, glass has become one of the most widely used and popular building materials of the age. This is partially because it’s aesthetically pleasing and partially because humanity has been using glass for such a long time that we have gotten rather good at it. Constant improvements in technology and understanding of thermodynamics has given us an excellent understanding of how – and why – heat is transferred through windows.

The full spectrum of light is far broader than what we can see. In fact, the light spectrum includes something that many people do not even think of as light because we don’t see it, we feel it: heat.

Beyond the range of wavelengths that we can see – wavelengths of about 380-780 nanometers – there are both larger and smaller wavelengths. UV light, at a wavelength of about 310-380 nanometers, is the type of light which fades interior finishings and may cause damage to the eyes. At the other end, at 780 wavelengths, there is infrared light which we feel as heat energy.

By blocking the light which we cannot see, Low-E glass coating allows us to protect our furniture from fading, taking some of the load off our heating and air conditioning, and still have a beautiful, unobstructed view of the outdoors.

The coating also prevents another common cause of heat transfer through windows, which is radiant energy. When the surface of the glass heats up, it naturally passes on some of that heat to the air around it, on both sides of the pane. By preventing the glass from heating up, the coating also prevents this radiant heat transfer.

Low-E coatings come in two types, but both are microscopically thin, transparent coatings that reflect long-wave infrared energy (heat) instead of absorbing it. The constant reflection of heat back into the home will also help maintain the correct temperature during cold winters.

Hard Coat

Also known as passive Low-E coatings, this type is applied to the glass surface during production using the pyrolytic process. It is fused to surface of the glass while it’s hot, creating a very strong bond that remains durable throughout fabrication. The glass is then cut to shape and turned into windows to be sold. This style of coating is best for cold climate as it will allow for some of the sun’s energy to enter the home, assisting with heating.

Soft Coat

Solar control Low-E coatings – or soft coats – are applied to pre-cut sections of room temperature glass in a vacuum chamber. They are then sealed in IG or a laminated unit and offer a lower level of heat emissions and improved solar control. Ideal for warmer climates, these windows work best for those who are trying to keep hot air out, not in. For those living in Canada, a hard coat would be better suggested.

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