Low-E Glass Windows (How Do They Work?)

Windows impact your home’s comfort level, which is why many types of glass materials are available. Low-E (Low-Emissivity) glass windows should be on your radar. They have a coating that enhances thermal performance and prevents energy loss, improving the overall energy efficiency of your home and helping you cut energy costs.

Below, I’ve outlined everything you need to know about Low-E windows so you can make an informed decision for your window replacement project and energy bills.

Here is one of our top window replacement companies, Renewal by Andersen. Contact them to receive a free quote on getting Low-E glass windows installed in your home.

Renewal by Andersen

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(833) 764-0526

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• Price Range: $1,200+
• Glass and Hardware Warranty: 10–20 years
• Labor Warranty: 2 years
• BBB Rating: A+
• State Availability: 47 states

• Installs its own patented Fibrex framing
• Includes a transferable 20-year warranty on glass and a 10-year warranty on nonglass materials
• Holds an A+ rating with the Better Business Bureau

• Doesn’t carry aluminum, fiberglass, or wood frames
• Can have long wait times between consultation and installation, according to customer reviews

You can purchase the following window styles from Renewal by Andersen:

• Awning
• Bay/bow
• Casement
• Double-hung
• Picture
• Sliding/gliding
• Specialty windows with geometric shapes

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What Is a Low-E Glass Window?

Low-E is short for Low-Emissivity or Low-Emittance. Low-E glass windows feature a transparent coating that’s thinner than a strand of human hair — it’s microscopic. Low-E coatings reflect long-wave infrared energy to prevent heat loss inside during winter and allow hot air to escape during summer.

Depending on how these coatings are applied to your windows, they can make the glass appear tinted. However, this tint shouldn’t impact your visibility out of the window, though it’ll deflect ultraviolet (UV) rays.

How Do Low-E Glass Windows Work?

Energy-efficient windows have an extremely thin coating that’s reflective. This coating minimizes UV and infrared light entering or leaving the home. In fact, this coating only allows light of a particular wavelength and frequency (visible light) to penetrate the glass.

UV light can cause fabrics and wall coverings to fade over time. Infrared light, also known as heat energy, can transmit heat into or out of a building. By blocking UV and infrared light, Low-E glass windows protect your furniture and decor while also keeping heat out during the summer and in during the winter.

What Makes Low-E Glass Energy Efficient?

Around 25% to 30% of your heating and cooling compensates for heat gain or heat loss through your home’s windows. However, Low-E coatings improve a window’s insulation thanks to their ability to block infrared light. This can reduce your energy costs by keeping hot air out during the summer, reducing the energy usage of your air conditioner. In the winter, the coating prevents inside hot air from escaping, reducing the energy usage of your heater. 

Benefits of Low-E Glass

There are many reasons why homeowners switch to Low-E glass. Here are just some of the advantages.

Enjoy Energy Savings

Low-E glass can cut energy loss by 30% to 50%. This helps keep your home at an optimal temperature, while also reducing the energy required to run your heating, ventilation, and air conditioning (HVAC) system. This all translates to lower energy bills. If you get double-pane glass with a Low-E coating, you can realize further energy savings.

However, it’s important to note that Low-E glass windows can also cost 10% to 15% more up front compared to regular windows.

Reduce UV Damage to Your Belongings

The sun’s rays can penetrate through glass, damaging your household items and fabrics. This harsh sunlight exposure can make your sofa look more worn and cause pictures to fade. Low-E windows block UV radiation to protect your upholstery, decor, and walls, keeping them looking brighter and in tip-top condition for longer.

On a sunny day, do you have to draw the curtains so you can view the TV or see your computer screen clearly? Low-E glass deflects infrared light to reduce glare.

Less Condensation

Condensation can form on glass windows due to hot air coming into contact with a cold window pane. This is particularly common during the colder months when you have the heating on. Condensation doesn’t seem like a big issue, but it can contribute to mold and mildew buildup, which has health implications. It can also damage your window frames if left unchecked.

Increased Window Durability

For safety reasons, your windows must act as a reliable, solid barrier between the inside of your home and the outside world. While Low-E glass has a thin coating, some types can be exceptionally strong, such as tempered Low-E glass windows or Low-E windows that have a hard coat.

Low-E glass is also worth the investment if you live in a climate that’s prone to hurricanes or severe weather.

Types of Low-E Coating

These are two types of low-E glass available, commonly known as hard coat and soft coat. Both are unique and have their own benefits. Here’s a quick review of the differences:

Hard Coat Low-E Glass

Also known as passive Low-E coatings or pyrolytic coatings, hard coat glass receives its Low-E coating during the float glass production process. This results in increased durability and reduced heat loss, especially in cooler climates. It doesn’t have to be sealed in an insulated glass unit, which means it can be used in single-glaze windows.

Hard coat Low-E glass tends to be less expensive compared to soft coat Low-E glass, but it’s also less energy efficient.

Soft Coat Low-E Glass

For homeowners concerned more with energy efficiency than window durability, soft coat Low-E glass windows may be the best option. This type of Low-E glass is often called “sputtered,” as it’s created using the Magnetron Sputter Vacuum Deposition (MSVD) process. You may also see it referred to as “solar control.” Multiple layers of metal or metallic oxides, such as silver, are placed into the glass. This gives the manufacturer superior control over coating thickness and energy efficiency capabilities.

Soft coat Low-E glass windows are ideal for warmer climates and extreme temperatures. They also offer more tinting and reflectivity compared to hard coat Low-E glass but tend to be more expensive and less durable.

Low-E Coating Performance Measures

Not all Low-E glass windows offer the same energy efficiency capabilities. They’re rated on different performance measures to determine the effectiveness of the glass and coating.

All Low-E glass is rated on:

• Thermal transmittance (U-value or U-factor) is how much heat loss the window allows. A lower U-value means higher energy efficiency.
• Solar heat gain coefficient (SHGC) is the fraction of solar radiation that goes through a window and is released as heat into the home. The lower the SHGC, the less solar heat the window transmits and the better its shading abilities. The higher the SHGC, the more effective it is at collecting solar heat during winter months.
• Visible transmittance (VT), also known as visible light transmittance (VLT), measures how much visible light is able to pass through the glass. The higher the VT rating, the more visible light is transmitted into a space.
• Light-to-solar gain (LSG) is the ratio between the SHGC and the VT. Higher ratings mean more light is transmitted while also not transmitting a lot of heat. Not all Low-E glass window manufacturers will provide this information.

How To Tell if You Have Low-E Glass Windows

If you’re unsure about whether your windows have Low-E coating, here’s how to tell:

• Light a match and hold it up to the window.
• You’ll see four reflections of the flame against the window.
• If you have double-pane windows, the four images will be the same color.
• If you have Low-E glass, one of the four reflections will appear a slightly different color than the rest.

You may also notice a slight blue-green shade on the glass at certain angles.

Our Top Recommendations for Low-E Glass Windows

Many manufacturers sell Low-E glass windows, but here are our two top recommendations to help you get started:

Stanek^® Comfort-Gard^® XTREME

Stanek^® Windows‘ energy efficiency glass consists of triple glazing, two layers of argon gas, and two layers of soft coat Low-E. It also comes with warm-edge spacer technology to lower heat transfer. These windows are ENERGY STAR rated in all climate zones within the United States.

JELD-WEN

JELD-WEN’s Low-E windows are available in various glass types: SunResist™, SunStable™, SunFlow™, HeatSave™, and Turtle Glass. Customers can choose between single-, double-, and triple-coating options.

Turtle Glass, in particular, reduces glare. HeatSave™ focuses on keeping heat inside your home, and SunStable™ blocks harmful UV rays while allowing some sunlight to shine through.

Here’s our full review of JELD-WEN window company.

Final Verdict: Are Low-E Glass Windows Worth It?

Low-E glass windows are a fantastic option for homeowners looking to improve the energy efficiency of their homes. They keep heat out during the warm months and heat in during the cold months, lower energy bills, and lower HVAC demands. Long-lasting and durable, they should be a top consideration if you’re thinking about replacing your windows.

Read our guide on best window brands to find an installer near you.