Nowadays, energy-efficient windows are crucial to lowering your bills, preventing drafts or air leakage, and helping you save the environment. Energy-efficient products have been helping people save thousands of dollars for decades. With new technological improvements every year, this can only benefit more people in the long run.

One of the main ways products are rated for their energy efficiency is with the Energy Star certification. The Energy Star rating for windows is an important standard widely used in the United States and applied to a range of products to show how energy-efficient it is.

But what is the Energy Star certification? How is this rating justified, and why should homeowners care? This guide will help you understand the Energy Star rating for windows and why it matters.

Understanding Energy Star Rating For Windows

The governing bodies determine Energy Star rating for windows, and to become certified, a window must meet a list of requirements. Once a window has the Energy Star label on a product, this means that the window is certified energy-efficient.

Knowing the Energy Star rating for windows can benefit homeowners.

Energy Star determines its ratings based on information from the National Fenestration Rating Council (NFRC), which tests windows in five categories across four different U.S. regions. The performance ratings are based on U-factor, a window’s solar heat gain coefficient (SHGC), air leakage, visible transmittance, and condensation resistance. The value of the scores depends on your region (Northern, North Central, South Central, and Southern).

But, having an Energy Star label on a window tells you it’s energy-efficient, while the NFRC label breaks down why giving you the ratings across all categories. It’s important to note that Energy Star only uses the U-factor and SHGC to decide, but you should still consider all the ratings to choose the best windows for your home.

What Makes Energy Star Windows Energy Efficient?

With over 90% of consumers recognizing the Energy Star symbol, it is an extremely useful tool to aid in the search for the best energy-efficient windows in the market. But what makes these certified windows great?

Energy Star products are low-maintenance materials designed for maximum insulation and durability.

The glass is of Low-E quality, reflecting infrared light to keep heat inside during the winter and outside during the summer and stops the ultraviolet light from reaching the upholstery, such as seats and carpets.

Between the panes in some certified windows is a special type of gas (either argon or krypton) that is odorless, colorless, non-toxic, and a better insulator than regular air.

There is also a warm edge spacer at the point of attachment between the glasses and the frame, which keeps the panes separated by the right margin and insulated at the edges to minimize heat transfer between them.

How Are the Most Energy-Efficient Windows Made?

Certain features in windows make them more energy-efficient. The best energy-efficient windows will have multiple panes, a Low E coating, gas fill, and ideal framing materials. But what makes those features effective?

Multiple Glass Panes

A double-pane window involves two sheets of glass separated by a spacer, and a triple-pane window consists of three. Between the layers of glass is an airspace that’s filled with air or glass, which acts as insulation. Because more is better, to a degree, triple-pane windows are better insulated. Of course, this is contingent on the window being built well and not having leaks.

Low E Coating

The Low E coating on a window is a microscopically thin layer of metallic oxide added to the glass surface to reduce the amount of heat emitted through a window. This goes for letting heat in and letting heat out. It effectively reduces the energy your HVAC system uses to keep your house cool or warm compared to windows without this coating.

It also helps block UV rays, which can discolor and fade fabrics and flooring, thus preserving your home’s interiors.

Gas Fill

Gas fill in multi-pane windows are a better insulator than air alone because gas is better at reducing heat loss. Krypton and argon are the standard gasses used in energy-efficient windows. Krypton performs better but is more expensive, which is reflected in the price of the window. Some manufacturers will use a blend of krypton and argon to create an effective but affordable non-toxic combination.

Window Framing Materials

Different framing materials will affect how energy-efficient a window will be. The best material for energy efficiency is fiberglass. Fiberglass window frames are more stable, making them structurally more likely to reduce air leakage. They also have insulated air cavities, making them thermally superior to other materials.

Vinyl and wood are also good insulators, depending on how they’re made. Composite wood tends to be a better performer regarding energy efficiency. Metals, like aluminum, conduct heat and cold, making them least efficient, if at all.

How Is the Energy Star Rating for Windows Measured?

Energy Star window ratings will vary depending on different attributes. For example, for a washing machine to be certified, it would need to use 25% less energy and 33% less water than normal washing machines on the market.

Energy performance ratings are evaluated using the following:


U-factor refers to the rate of non-solar heat transfer from warm to cold areas. It tells you how well a window, door, or skylight insulates. It ranges from 0.25 to 1.25 watts per square meter Kelvin (W/m2K). The lower the U-factor, the better.

Solar Heat Gain Coefficient (SHGC)

SHGC numbers illustrate the ratio or the fraction of solar radiation transmitted directly to and absorbed by the windows and released as heat inside the house. A lower SHGC rating indicates excellent shading ability, which is great during the summer months because it blocks the heat emitted from the sun.

On the other hand, a high SHGC rating will keep the home warm during the cold winter season. Your home’s location, climate, and external shading will all play a pivotal role in determining the best SHGC rating for you.

Centre of Glass Rating

Homeowners can save on utility bills with energy efficient windows.

As the name suggests, this specifically measures the energy efficiency rating of the glass portion of windows, doors, and skylights.

Visible Transmittance (VT)

Visible transmittance is an optical criterion and is different from SHGC. It measures a fraction of the amount of visible light that can pass through the glazing material of a window. A higher VT means a window can usher in plenty of natural light.

When designed smartly, your home will be able to maximize daylight and conserve energy.

Why Are Energy Star Windows Preferred by Homeowners?

The core purpose of energy star rating for windows is to help the country save energy by encouraging manufacturers to produce “greener” products through “greener” solutions. However, consumers have been the biggest beneficiaries of the whole program.

Windows are an important feature of any home. They allow you to control any space’s natural lighting and temperature while providing ample visibility to the surrounding environment.

Certified windows have been tested to minimize heat loss and air leakage. But what are the other benefits of an Energy Star-certified window?

1. Cost Savings

Certified windows help reduce the cost of your energy bills each month. The more efficient your windows and doors are, the less energy is required to cool and heat your home.

Compared to non-certified windows, Energy Star products reduce energy costs by approximately 12%. Your savings will depend on your local weather conditions, home design, and utility costs.

2. Increased Comfort

Energy efficient windows can help you save on HVAC bills.

High-quality windows, doors, and other products help you create a consistent temperature throughout your home—even under extreme weather conditions.

3. Home Protection

Your home’s windows can make its interior vulnerable to damage from sunlight. Certified windows have a unique coating that protects your interior from harmful ultraviolet (UV) light.

When exposed to the sun’s UV rays, it’s not uncommon to damage wood floors, curtains, and other personal possessions within your home. Energy Star windows protect these items from losing color and integrity over time.

Do you want to know more about the Energy Star rating for windows, or are you planning to have certified windows installed in your home? Please contact us today!

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Woodway, TX 76712
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