What is Low-E Glass in Windows?

Low-E (low emissivity) glass is a glass coated in materials meant to improve its thermal performance. What does that mean?

Better Insulation
Better (Wanted) Heat Retention
Better Blocking of (Unwanted) Heat
Maintaining Entrance of Natural Light

Read on to find out how Low-E glass works and why home improvement companies like ours think it’s the right choice for your home.

What is Low-E Window Glass?

Low-E window glass is glass with a low level of emissivity.

What is emissivity?

Emissivity is the ability of a material to emit energy as thermal radiation.

What is thermal radiation?

In windows, thermal radiation includes infrared radiation (IR), optical (visible) light, and ultraviolet radiation (UV).

Clear (uncoated) glass is naturally a highly emissive material that produces lots of thermal radiation, Low-E coatings provide more control over thermal radiation. High-performance Low-E windows are designed to keep a house’s temperature consistent reflecting the interior temperatures back inside while blocking exterior temperatures from passing through the glass.

Low-E window glass:

Keeps heat on the side of the glass where it originated
Allows natural light to enter your home
Blocks damaging UV rays

How Does Low-E Glass Work?

Low-E glass windows have an extremely thin, transparent coat that works to reflect heat and while allowing natural light to pass through the window.

Coatings are applied through two primary methods:

Pyrolytic chemical vapor deposition (and)
Magnetron sputtering

Let’s talk about the magnetron sputtering. This method involves depositing several alternating layers of silver and antireflection onto the glass. The low-e coating should reduce the emission of radiant infrared (invisible) radiation meaning heat will stay on the side of the glass where it originated and (visible) light will still pass through the glass.

Heat originating inside stays inside = warm winter/low heat loss
Heat originating outside stays outside = cool interior (A/C on)/low heat gain

Low-e glass reduces emissivity ultimately improving the insulating properties of the window allowing it to protect your comfort from external temperatures in any climate.

Types of Low-E Coatings?

The two main types of Low-E coatings are Passive Low-E Coatings and Solar Control Low-E Coatings.

Passive Low-E Coatings, otherwise known as a hard-coat, are made using the pyrolytic method. Pyrolytic coatings are applied at high temperatures and are considered a medium grade quality coating. A medium grade coating performs much better than plain clear glass.

Solar Control Low-E Coatings, otherwise known as a soft-coat, are made using the magnetron sputtering method. In this process, glass is placed in a vacuum chamber and alternating layers of silver and antireflective properties are applied. The soft-coat has lower emissivity and superior solar control performance while delivering the highest performing solar control.

Most window companies use glass made by Cardinal Glass Industries↗ which offer a variety of Low-E glass options, including the widely used LoĒ³-366®↗.

Learn More: What is Insulated Glass?

Pros and Cons of Low-E Glass

Benefits of Windows with Low-E Glass

1 - Limits the amount of UV rays that enter through the glass. In addition to being harmful to our skin, UV rays can cause the color of furniture and fabric to fade.

2 - Reflects the temperature back to the side it originated on. Reflecting heat or cold back inside the house improves energy efficiency and lowers energy bills. Additionally, it helps keep your home at a comfortable temperature.

Drawbacks of Windows with Low-E Glass

1- Glass with Low-E coatings is more expensive than clear glass. The advantages of Low-E glass come at a higher initial cost but may result in more savings and comfort over time.

2 - The glass is not clear. Although the glass provides lots of natural light, the color of the glass from the exterior is not transparent. Some color variations are more noticeable than others.

How Can I Tell If My Windows Have Low-E Glass?

Low-e coatings aren’t always visible, if you suspect that your windows have Low-E Glass, a good way to tell is by holding a lit match or a pen up to the window’s reflection. Follow the steps below from Geo Shield↗ to test for Low-E coating in a double-pane window:

Using a lighter or laser, hold it close to the glass and look at the 4 reflections
1 of the 4 should be a slightly clearer and different color
This indicates the presence of Low-E glass
No differences in reflection means no Low-E

Which Type of Low-E Coating is Best For My Climate?

Understanding your climate is an important factor when considering Low-E coatings. Manufacturers offer a variety of options because Low-E windows are designed to be effective in specific climates. Low-e windows are made for high, medium, and low solar heat gains.

HIGH SOLAR GAIN LOW-E GLASS - COLD CLIMATES

It is designed to reduce heat loss while permitting solar heat gain. Usually made with hard-coat Low-E glass.

MEDIUM SOLAR GAIN LOW-E GLASS - MODERATE CLIMATES

Reduces heat loss while and permits moderate solar heat gain. Usually made with soft-coat Low-E glass.

LOW SOLAR GAIN LOW-E GLASS - HOT CLIMATES

Blocks heat transmission. Made with soft-coat Low-E glass with several layers of silver.

Who Makes Low-E Glass?

The biggest manufacturer of Low-E glass is Cardinal Glass Industries, in fact, Cardinal provides glass for most window companies. Cardinal makes insulated, coated (Low-E), laminated, tempered, and float glass. Its Low-E options include the following:

LoE-366
LoE-240
LoE-Glass
LoE-340
LoE-189
LoE-180
LoE-180ESC

If you know Low-E glass will be part of your purchase, make sure you ask your window consultant what options are available to you and which make the most sense for your climate.

Your windows provide more than light and a barrier against wind, understanding the value of insulating materials like Low-E glass will help you design the best window for your home and budget. Though Low-E glass can involve a larger initial investment, it could pay off in the long run if you’re looking to influence the light and warmth that windows bring into your home.

Andersen is one of the major window companies offering many Low-E glass options for their windows, check out our Andersen products to learn more about energy-efficient glass options for windows.