Explained: Energy Star Ratings for Windows

An Energy Star rating can help you choose a window with the right features for your climate. And since windows last for decades, choosing high-quality energy efficiency options is important.

But, if you’re unfamiliar with windows, terms like U-Factor and SHGC on an Energy Star label can seem like a foreign language. Read this guide to learn how to decode Energy Star ratings and choose the best window for your home.

What is an Energy Star Rating?

Energy Star Ratings for Windows

Energy Star is the United States government symbol declaring a product is energy efficient. The NFRC (National Fenestration Rating Council) is a government program that tests, compares, and certifies Energy Star products.

How to Read a Window Energy Star Rating

If a window is certified Energy Star, it’s at least somewhat energy efficient. You can learn what the terms on the labels mean to pick an even better option for your home.

If you’re shopping for windows, these are the listings you’ll see on an Energy Star window rating.


The U-Factor is one of the most critical window ratings, showing how well a window insulates or transfers non-solar heat. A label that lists “U-Factor” refers to the window’s glass. If the rating is marked “NFRC U-Factor,” it relates to the entire unit, including glass, frame material, and spacer.

A typical U-Factor ranges from .20 to 1.20. The lower the number, the better the window insulates. In most circumstances, you’ll want a U-Factor of .30 or below.


SHGC stands for solar heat gain coefficient and measures how much solar heat a window allows into the home. A low SHGC rating means the window transfers little heat into the house. A low SHGC is ideal for warm, sunny climates, but a higher SHGC is better for year-round cold temperatures.

A typical SHGC range is 0 to 1, with 0 being no solar heat gain.

Air Leakage (AL)

Air leakage measures the rate of air movement through a window at a specific pressure. The air leakage rating will range from 0.1 to 0.3. The lower the number, the lower amount of air leakage a window has.

Important note: A window with the lowest air leakage can still be drafty if not correctly installed. Proper installation is crucial for energy-efficient windows.

Visible Transmittance

Visible transmittance measures how much sunlight comes through the window. A high visible transmittance rating lets in the most sunlight. These ratings go from 0 to 1.

Condensation Resistance

Condensation can occur when the inside of a home is hot and the outside is cold or vice versa. Too much condensation leads to problems like mold or rotting, especially in wooden frames.

The condensation resistance measures how well a window resists condensation. The ratings go from 0 to 100, and the higher the number, the less likely the window is to experience condensation issues.

Do Energy Star Ratings Vary By Region?

Energy Star ratings vary by region. The two window factors that change are the U-Factor and SHGC.

Do Energy Star Ratings Vary By Region

Here’s what you should look for depending on where you live:

Northern Climate

The Energy Star rating for a northern climate is different from the rest. Rather than one broad number, they provide three ratings you can look for.

  • U-Factor of .28 and SHGC of >.32
  • U-Factor of .29 and SHGC of >.37
  • U-Factor of .30 and SHGC of >.42

North Central Climate

  • U-Factor: <.30
  • SHGC: <.40

South Central Climate

  • U Factor: <.30
  • SHGC: <.25

Southern Climate

  • U Factor: <.40
  • SHGC: <.25

What Does the Map Mean on an Energy Star Rating?

Windows with an Energy Star rating will feature a map of the United States with certain areas shaded in light blue. The blue shading signifies if a window is Energy Star rated in that area.

Since different climates require different ratings, the map is an easy way to tell if you’re picking a product that will be suitable for your home.

Are All Window Frames Energy Star Rated?

While not all windows are Energy Star rated, all window frame materials can be Energy Star rated. The most energy-efficient window frame material is fiberglass, followed by wood, wood clad, and vinyl.

Aluminum is the least energy-efficient frame material, but newer versions feature thermal breaks for improved insulation.

Here’s the good news: if you’re getting ready to purchase new windows from a reputable brand, there’s a high chance the material and window are Energy Star rated.

Are Energy Star Windows Worth It?

According to the Department of Energy, windows are responsible for 25 to 30% of heat gain and loss. So replacing your old, drafty windows with new energy-efficient versions will regulate indoor temperatures and help cut energy bills.

An Energy Star rating is the government’s way of certifying whether or not a product will be energy efficient. So, if you are replacing your windows, going with an Energy Star product is worth it. Windows should last decades, so choosing a quality, long-lasting, energy-saving product is essential.

Frequently Asked Questions (FAQ)FAQ

Is .30 a good U-Factor for windows?

A .30 is a good U-Factor for all climates. If you live in a cold northern climate and choose a window with a .30 U-Factor, ensure that the SHGC is at least .42

Is .27 a good U-Factor for windows?

A .27 U-Factor is excellent, signifying that the window insulates well and will prevent heat from escaping the home.

Does Low-E glass make a window Energy Star rated?

Low-E glass is essential in how well a window insulates and, in some cases, how well it reflects solar heat. While it’s common for windows with Low-E glass to have good Energy Star ratings, just because a window has Low-E doesn’t mean it’s rated.

Where can you buy Energy-Star-rated windows?

You can purchase Energy-Star rated windows from the big box stores like Lowes, Home Depot, or Menards. You can also get Energy Star-rated windows from top brands, including Pella, Andersen, Milgard, Jeld WEN, Champion, and more.

Final Thoughts

Choosing an Energy Star-rated window will guarantee at least some energy efficiency. By learning how to read the label, you can find a window that fits all of your needs. The two most important numbers on Energy Star ratings are the U-Factor, which determines how well a window insulates, and the SHGC, which measures how much solar heat a window conducts.

Areas with cold climates need a low U-Factor and higher SHGC, while hot sunny climates need low U-Factors and low SHGC. Also, remember that even the best-rated windows won’t perform well without proper installation.