What is Low-E Glass & Does it Make Windows Energy Efficient?

Low E coatings on the glass surface help manage the amount of light and heat either conducted through a window or reflected away from it, reducing a home’s dependence on energy-consuming climate control systems. The national ENERGY STAR® program recognizes products that meet strict energy-efficiency guidelines to suit climates in different areas of the country. Marvin Family of Brands offers products to meet climate and code requirements for various markets across the country.

Low E1
Suitable when maximum solar heat gain is desired balanced with the radiant heat properties of a single Low E coating. Generally used in Northern climates where heating is prioritized overcooling. Maximum benefits are achieved when used on elevations with direct sun exposure.

Low E2
The most common Low E coating since it works well across most geographic regions and climates. Low E2 with two metallic coatings balances less solar heat gain along with improved radiant heat transfer properties over Low E1.

Low E3
Used in applications where solar heat gain may be a concern with multiple metallic layers offering radiant heating properties similar to Low E2. Most commonly used in Southern, sunny climates where cooling is prioritized overheating.

A higher performing Low E glass with significantly improved U Factors. This coating resides on the interior surface of the glass and can be touched. It is used in conjunction with Low E2 or Low E3. This coating is effective at reflecting radiant heat back into the room. This means a slightly cooler interior glass surface since the heat is not absorbed by the glass. The cooler surface may see a bit more condensation in cold climates versus traditional Low E glass make-ups. Also, abrasive products must be avoided when cleaning the glass.

Learn more about energy performance ratings.


glass ig units
This table compares the room-side center of glass temperatures of different glass types against two different winter conditions.


low e glassreplacement windows
LowE³-366® glass is the ultimate performance glass. It just might make all other Low-E glass obsolete.

We recommend Cardinal LoĒ³-366® Glass

When the temperature soars, ordinary window glass can’t handle the heat. And tinted glass spoils the view. Cardinal Loå³-366, however, has been specially formulated to reject the sun’s heat without affecting the view. It lets more light in and keeps more heat out. So your home stays cool and comfortable. Our patented LoE-366 coating provides the ultimate in performance of all our LoE products.

It’s also the one glass you can use to be compliant in every ENERGY STAR zone – in a double-pane window. Couple it with LoĒ-i89®, and you’re compliant in the North. Its low SHGC makes it compliant throughout the rest of the country as well. It’s the perfect glass wherever you live.

Beats the heat and Keeps the view.

For years, Cardinal has been setting the standard for energy efficient glass. Top-of-the-line residential window and door manufacturers all rely on our high quality. Our patented state-of-the-art sputter coating processes are unmatched by any other glass manufacturer.

What’s more, LoĒ³-366 provides exceptional fading protection as well. It blocks 95% of the sun’s damaging ultraviolet rays (a leading cause of fading), so it will help your furniture, carpets, curtains and wall coverings stay beautiful for years to come.

It’s the perfect cold remedy, too.

During cold weather, the insulating effect of your windows has a direct impact on how your rooms feel. Typically, 75% of the exposed surface of a window is glass, and the temperature of the room-side of the glass directly affects the air temperature in the room. The better insulated the window glass, the warmer your room will be.

The Efficient Windows Collaborative (www.efficientwindows.org) suggests that when glass surface temperatures fall below 52°F, there is a risk of thermal discomfort. To maintain the best comfort during the winter, select a glass product that produces surface temperatures that will stay above this point during the coldest outdoor conditions.

The superior insulating capability of Cardinal LoĒ³-366 is a crucial factor in the construction of comfortable windows for cold climates. The dramatic comfort improvement from windows with warm glass surfaces also means the relative humidity of the indoor air can be controlled and maintained correctly. Proper humidity levels (not too much, not too little) will improve comfort and promote a healthier living environment.

Three layers of silver make a clear difference.

For years, Cardinal has been setting the standard for energy efficient glass. Top-of-the-line residential window and door manufacturers all rely on our high quality. Our patented state-of-the-art sputter coating processes are unmatched by any other glass manufacturer.

Now we’ve raised the bar.  LoĒ³-366 adds a third layer of silver coating. Result: a clear coating that blocks, even more, solar gain, reflects heat, and lets the light stream in. LoĒ³-366 outperforms the tinted glass often used in warm climates.

You’re always in season with LoĒ³-366 glass.

LoĒ³-366is the ultimate performance glass, with energy savings throughout the year, in every part of the country. All with exceptional visibility. It’s the perfect glass wherever you live.

LoĒ³-366 can be purchased with any Infinity from Marvin window, at Gravina's Window Center of Littleton,  in a variety of shapes and sizes.  Call us now for more info!

Read more at Cardinal Glass

Labeling and certification ensures product quality, allowing consumers to trust claims of window product performance prior to buying.