The Lowdown on Low-E: What You Need to Know

Last Updated on March 9, 2022 by Kravelv

Sunlight can easily heat up your home when it enters through your doors and windows. And when it heats up, your home relies on your cooling system to bring down indoor temperature to a suitable level. The hotter your home, the harder your cooling system has to work, which makes your energy bills spike.

High monthly bills can be problematic so homeowners have begun exploring what they can do to make their properties more energy-efficient. There is no going around using energy in the home, after all. To address this concern, the window industry came up with low-emissivity, or low-E, window glass, providing homeowners with a simple yet effective way to improve energy efficiency in their properties.

What is low-E and what can it do for your home? In this post, you’ll see why low-E glass is worthy of your attention.

What is Low-E Glass?

Low-e windows were first invented in the 1980s and only came in one variety, designed to keep solar heat trapped in the home to ease heating needs in colder climates. The window glass features a microscopic layer of metal or metallic oxide, which is so thin so the coating is virtually invisible and doesn’t impede the level of natural light that the window lets in.

Today, however, Low-E coating can be applied on the inner, outer, or both sides of a window depending on a home’s heating and cooling needs. Wherever it’s used, low-E glass is highly insulative, thanks to the gas fill it uses that helps stunt heat transfer through multi-pane windows.

What’s the “E” in Low-E?

“E” stands for emissivity, the ability of a material to radiate or emit energy. When heat or light hits glass, they are either convected away by moving air or re-radiated by the glass itself. All materials actually have the ability to emit or radiate heat in the form of long-wave, far-infrared energy depending on their temperature. In general, highly reflective or light-colored materials have lower emissivity while dull, darker-colored surfaces have higher emissivity.

The types of energy that come from the sun are ultraviolet (UV) light, visible light, and infrared (IR) light. They all occupy different parts of the solar energy spectrum. Basically, low-E glass controls which and how much of these energy types pass through the glass surface, and which and how much of them are reflected away.

Types of Low-E Glass

Low-E glass can be categorized according to the manner by which the coating was applied:

• Hard Coat (online). This type of low-E glass is coated with thin metallic oxide layer during the manufacturing process. Because of this, the coating is effectively welded to the glass surface, making it more durable and more long-lasting. Hard-coat low-E glass also generally has higher U-values than the soft-coat option but is also hazier in appearance.

• Soft Coat (offline). This type of low-e glass is coated after the glass has been formed. Also known as sputter coating, it is less commonly used than its hard-coat counterpart but is not as hazy so it lets in more visible light. Soft-coat low-E glass also has excellent U-values but is less durable than the hard-coat option, making it easier to scratch.

The Benefits of Low-E Glass Today

As mentioned earlier, the first low-E windows were designed to primarily keep the heat in. Today, however, low-E products do not only keep indoor heat in but also outdoor heat out. As it is an added feature, low-E coating does make window glass cost about 10% to 15% higher than what standard windows go for, but the higher price tag does help reduce energy loss by 30% to 50%, helping you save on your monthly energy bill in the long run.

Choosing a Low-E Window

If you want to make the most of low-E windows, choose what will work best for your local climate. In areas that are generally cold, for instance, heating needs will be higher so low-E windows with coating on the glass’ inner side will be ideal, as this will keep indoor heat in. In areas that are generally hot, on the other hand, opt for the reverse: low-E windows with coating on the glass’ outer side. This will help in managing cooling needs as the low-E window will be keeping outdoor heat out.   

Getting to know low-E windows is important if you want to know exactly how they can help in your aim to make your home more energy-efficient. To make the most of getting low-E windows as replacements, make sure you work only with a reputable contractor in your area.

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Author Bio:

Joe Ronzino is the president of Renewal by Andersen of Long Island. A lifelong Long Islander, he has vast experience in the replacement window and home remodeling industries, with roots in the home improvement business going back to the mid-70s. His experience combined with advanced training from Renewal by Andersen give him what it takes to make Long Island customers happy. For updates from Joe, check out the company blog!
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