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The Highs of Low-E Glass: How It Works

The Highs of Low-E Glass: How It Works

Glass is among the most widely used and versatile building materials. In fact, anyone would be hard-pressed to find a home or building without it. Windows and doors, in particular, are made more attractive and efficient by glass.

Nowadays, “Low-E” is a term that we often hear or read about when glass is being discussed. But, as not all of us may have full understanding of what it is and what it does, I am giving you this definitive guide to low-e glass for you to better understand what it is and how it works.


What is Low-E Glass?

Low-e glass is one of today’s technological marvels when it comes to building materials. The “E” in low-e stands for emissivity, the relative power of a surface to emit heat by radiation. In low-e glass, this relative power is basically lowered or minimized, if not totally eliminated. To achieve this, the glass is coated with a layer of transparent and microscopically thin metal.

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The Role of Low-E Glass Coatings

Low-e coatings have been developed to minimize the amount of ultraviolet and infrared light that can pass through the glass without compromising the amount of visible light transmission.

Standard clear glass typically absorbs 84% of the (heat) energy it receives, and only 16% is reflected away. Inversely, glass with low-e coatings can reflect away as much as 96% of the energy, absorbing only 4%. Considering these values, it can be said that conventional clear glazing allows in a significant amount of solar radiation and heat. This can make an indoor space warmer than you need or want it to be. You will also have to spend more on utilities as you try to make your home cooler.


Meanwhile, during winter, the reverse happens. Low-e glass will reflect the heat that will try to escape to the colder outdoors, back to the indoors. Temperatures are maintained due to the constant reflection that occurs.

As low-e coatings are basically thin layers of silver or metal, the glass acts like a metal thermos that helps regulate temperatures at the levels that you want them to be.

Measuring Low-E Performance

Fenestration products are evaluated and rated to guide customers on their energy performance. The following are used to measure the efficiency of products that have low-e glass.

U-Value or U-Factor. This is the rating given to a product based on how much heat loss it permits. The lower the rating, the better.

Visible Light Transmittance (VLT or VT). This measures how much light can pass through a product. The higher the rating, the better.

Solar Heat Gain Coefficient (SHGC). This measures the fraction of incident solar radiation allowed by the product. The lower the rating, the better.

Light to Solar Gain (LSG). This is the ratio between the SHGC and VLT. If value is greater than 1.0, it means that the glass transmits more light than heat.

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Benefits of Low-E Glass

Low-e glass, when used for the right applications and installed in the right places, can greatly help in enhancing a home’s energy efficiency and comfort. It can:

  • Enhance thermal protection

  • Help cut energy consumption up to 25%

  • Improve the window or door’s ability to filter out harmful UV rays

  • Make cleaning of the glass exterior easier

  • Reduce sound penetration

When deciding about windows and doors, it is normal to think about aesthetics and measurements first. But, you must remember that the quality of glass also plays an important role in the overall energy performance of a product. Learn more about low-e glass and how it can benefit you by consulting a professional contractor in your area.

About the Author

Alex Esler works as a Marketing Manager for Renewal by Andersen Southern MA. Their local, family-owned offices in Southern New England, Greater Philadelphia, and Colorado make up the largest replacement window company in a network of 100 Renewal by Andersen dealers. Always eager to help and known to maintain a positive outlook in life, Alex remains driven and inspired by her work and the causes she cares about. She shares her knowledge and experience by writing blogs during her free time.

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