Low E Glass Types Explained

There may be no building material more versatile than glass. It can truly do e

What Is Low-E Glass?

From the beginning: the "E" is for emissivity. When heat or light energy is absorbed by a surface, such as glass, it's either reflected off the surface, or radiated through the surface. A material's ability to radiate energy is known as emissivity. What does that have to do with your windows? If you've ever been in a greenhouse, you probably already know the answer to that question.

Radiating energy is one of the leading causes of heat transfer in window glass. Emissivity (or low-e) windows radiate less energy, and therefore transmit less heat, which gives them greatly enhanced insulating properties. When heat energy—either from the sun or from your HVAC—strikes a low-e window pane, it is reflected back into the space it came from instead of being transferred through the window.

How Low-E Glass Works

The secret to the remarkable insulating qualities of low-e windows is the thin metallic coating on the surface of the glass. Low-e windows often appear tinted, but low-e glass is not the same as tinted glass. Whereas tinted glass is made by adding alloying materials into the glass itself, low-e glass has a microscopically thin layer—often multiple layers—of various metallic particles on the surface. These layers turn the glass into something like a filter, or a sieve.

You see, different types of energy have different wavelengths. Infrared, for example, has a long wavelength, while the visible light spectrum has a relatively short wavelength. Different metals will "filter out" different wavelengths, so by adding thin layers of various metals onto the surface of the glass, it's possible to choose what types of energy get through.

If you want to filter out long wavelengths (infrared, i.e. heat) while allowing shorter wavelengths (light) to pass right through, low-e glass can do that. Most low-e glass also limits the amount of ultraviolet radiation that is allowed to pass through, which is beneficial both for the health of those who live in the home, as well as for the longevity of your furnishings.

Types of Low-E Glass

Several different metals are used to create the micro-thin layer on the surface of low-e glass. Tin, silver, and zinc are some of the most common, and many types of low-e glass utilize a combination of different metal layers. Still, with all the possible combinations, there are two basic types of low-e glass coatings: passive low-e coatings, and solar control low-e coatings. There's a crucial difference between the two.

• Passive low-e coatings are designed to maximize solar heat that passes into a building. This creates a “passive” heating effect, reducing the need for artificial heating. Windows with passive low-e coatings are ideal for colder climates.
• Solar control low-e coatings limit the amount of solar gain into a building. The purpose is to keep buildings cooler and reduce air conditioning usage. They are ideal for hot climates and homes that receive a lot of direct sunlight.

How Low-E Glass is Made

Low-e windows may be categorized as "hard coat" or "soft coat." Both passive and solar control low-e glass can be made through either method:

• Hard coat low-e glass: Manufactured through a pyrolytic process. A thin layer of molten metal is applied to a sheet of glass while still slightly molten, creating a strong bond.
• Soft coat low-e glass: Made via Magnetron Sputter Vacuum Deposition (MSVD). Metal particles are applied to pre-cut sheets of glass at room temperature in a vacuum chamber. The resulting coating is extremely thin and delicate.

Choosing Low-E Glass

Homeowners have a lot to consider when choosing new low-e replacement windows. The most crucial consideration is choosing the right windows for your climate, depending on whether you're most concerned about keeping your home cool during warm weather or warm in the winter. The right combination, when installed correctly, can do both.

Key window ratings to consider:

• U-Factor Values: How well a window prevents heat from escaping (lower = better insulation).
• Solar Heat Gain Coefficient (SHGC): Measures how well glass blocks heat from the sun (lower = better heat blocking).
• Visible Transmittance (VT): Measures how much light passes through (higher = more light).

Low-E Glass Manufacturers

The glass industry is dominated by Cardinal Glass Industries and Guardian Glass North America. These two companies supply the majority of window companies with high-performing glass packages.

Ready to learn more about low-e window glass? Contact us today to talk to our team about finding the perfect windows to maximize your home's comfort and energy efficiency.