What Is Low-E Glass?


Not all windows and glass products are created equal, but by understanding how heat and light interact with different materials, and with the latest technologies available today, glass manufacturers have been able to develop better and more efficient windows for your home. While you can select a basic pane of glass for your home’s windows that will adequately act as a barrier between yourself and the outdoors, why not choose materials, coatings and features that enhance your home’s functionality and make your daily living more comfortable and convenient?

When shopping for new windows for your home, you may have come across the term Low-E glass, or low-emissivity glass, but what exactly does it mean, and how does it affect the overall quality of your windows?

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What Is Low-Emissivity Glass?

To understand the features of Low-E glass, you must first understand the basics — the “e” in Low-E stands for emissivity. Emissivity is the ability of a material to radiate and transmit heat. Depending on the type of material, heat is either absorbed or reflected away. For example, a reflective, light-colored surface like aluminum foil has very low emissivity, while darkly colored surfaces such as asphalt have high emissivity and will get hot.

If you’ve ever stood near a window with a standard pane of glass, you may have been able to feel heat coming through the surface. To reduce the effects of heat transference through the glass — as well as other harmful effects of the sun, like ultraviolet (UV) light — Low-E glass coatings were developed.

These coatings are extremely thin layers applied to glass that allow the material to reflect that radiant energy. The Low-E coating works two different ways — it can either keep precious heating inside your home during cold months, preventing escape through the glass, or prevent heat from entering your home on a hot day.

To Summarize:

Simply put, a piece of ordinary glass is coated with a very thin, non-toxic coating. This coating makes the glass significantly more energy efficient by reducing the amount of solar energy allowed into a building through the glass in window openings. The purpose of the Low-E coating is to reduce the amount of solar radiation that enters a building from the infrared portion of the solar (sun’s) spectrum while still allowing a high degree of light to come into the building. The coating also helps to keep heat in a building during winter heating periods.  

 

low e glass energy efficiency

Different Types of Low-E Glass Available

During research about low-emissivity glass, it’s important to note that there are two different types of Low-E glass available — passive and solar coatings. A passive coating is intended to maximize the amount of solar heat entering the space to trap heat. The benefit of a passive Low-E glass coating is that it reduces the dependence on a heating system to keep your home warm. Solar coatings work in an opposite manner, minimizing the amount of solar heat entry and keeping buildings cooler.

Solar and passive coatings are manufactured with two different methods, either with a hard or soft coating. A hard coating technique is often used for manufacturing passive coatings, while soft coating is typically applied for making solar coats. However, these methods vary depending on the manufacturer.

Hard coatings are created by pouring a thin ribbon of hot tin onto the glass sheet, forming a strong bond between the metal and glass that makes it difficult to scratch or damage. Soft coating involves adding silver, zinc or tin into a vacuum chamber that’s filled with electrically charged inert gas. The vacuum then sputters the metal onto the glass, creating a soft layer.

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Benefits of Windows Featuring Low-Emissivity Glass

Depending on where a building is located and the size and number of window openings involved, the savings in both cooling and heating costs can be quite significant. There are numerous charts and performance evaluation materials available to help explain and analyze specific costs for those interested in more detailed information. As energy conservation concerns continue to be an essential component of everyday life, and as building code requirements also continue to become more stringent, Low-E coated glass products are currently being used in most new construction projects.  

Low-e glass sounds like it could be a useful tool for your home, but why should you spend the extra money? When your windows have Low-E glass installed, you’ll gain the following benefits:

  • Furnishing protection: One use of Low-E glass is filtering out harmful UV light. Not only is UV damaging for your health, but it also harms your furniture, causing fabrics to fade and deteriorating the quality of materials and flooring.
  • Improved window durability: The added layer in your window, although thin, will allow for extra durability, reducing chances of scratching or breakage.
  • Increased energy efficiency: With Low-E glass, your home will have added insulation, which will result in less heat transference from your interior to the outside. The reduction of heat loss will improve energy efficiency throughout your home. These low-emissivity windows can reduce energy losses by 30 to 50 percent.

What Low-E Glass Doesn’t Do

So you may ask—if low-e treated glass is pretty much the norm, why would there be any confusion about its use. The answer to this question is straightforward. In particular, there is a fair amount of misunderstanding about what Low-E doesnt do. 
 

  1. Low-e Glass Is Not a Safety Product unless it has been tempered or is incorporated into a laminated glass composition. On its own, the coating does not alter the glass in any way, nor does it make the glass stronger or safer.  
  1. Low-E Glass Does NotBlock All UV Rays. It does block some, but it will not prevent fabrics from fading or stop UV rays from hitting your skin. The ultimate UV Impact will vary from product to product. The actual performance data for the various Low-E products in today’s marketplace are readily available. 
  1. Not All Low-E Glass Products Are Created Equal. Numerous manufacturers make Low-E coated glass, and there are many variations in both color and performance. This becomes a real problem when a piece of glass with a Low-E coating needs to be replaced or matched. If the product initially used is not known, getting a color match can be very difficult. Most Low-E coatings are advertised as “color-neutral” or “colorless.” In certain light situations, they will appear to be gray, green, brown, or blue depending on the manufacturer of the product. 

Replacing Low-E Glass 

Most glass shops will tell the consumer that if the original Low-E glass’s exact manufacturer is not known, they will do the best they can to match the replacement glass to the original. Still, they cannot guarantee a perfect match. Many glass shops have sample kits with them when they measure a Low-E replacement glass. While this can be quite helpful, it is not always a successful solution. You should always attempt to record what glass was used in a given application, if possible.  

In residential applications, Low-E glass will have the coated surface of the glass concealed (or used) on the inside of an insulating glass unit. This means you cannot come in contact with the coated surface while you are cleaning the glass. This is a good thing. In other words, Low-E treated glass can and should be maintained just as any other glass product would be similarly treated. Remarkably, there have been reports of so-called special “Low-E Glass Cleaners” being sold to consumers (at prices higher than regular glass cleaners). It’s my opinion that these cleaners are not necessary for the consumer to buy.  

In conclusion, Low-E treated glass is a truly great product that has saved consumers untold sums of money by reducing energy consumption in homes and other buildings of all types and sizes. As with all technically oriented products, the better we understand how they work and what they can and/or cannot do, the better we will take advantage of them. It has often been said that the best consumer is an educated consumer. When it comes to glass products used in our residences and places of work, this is very true.  

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Glass.com attempts to provide accurate information but cannot be held liable for any information provided or omitted.  You should always work with a licensed, insured and reputable glass shop that can assess your specific needs and local building codes and offer professional services. Never attempt to cut, install, or otherwise work with glass yourself. All content is provided on an informational basis only.


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By Daniel Snow

Daniel Snow serves as the operations manager for Glass.com and is also a contributing editor. He earned a Bachelor’s Degree in Business Management from George Mason University and has a background in the real estate industry. After high school, Daniel even worked at a family-owned glass shop for a short period of time and is an Auto Glass Safety Council certified installer.

In his free time, Daniel enjoys being outdoors, especially around the water where he can be found surfing, fishing, and boating. He has a passion for bringing old vehicles back to life and loves working with his hands to restore cars, boats, and motorcycles.


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