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How to Read a Window Sticker & Other Elements To Know When Buying New Windows

When it comes to buying windows for your home, you have a lot of choices. From styles and colors, to materials and manufacturers, the amount of information and research out there can be overwhelming. When comparing windows side by side, many homeowners use the easiest resource to compare windows:

The National Fenestration Rating Council (NFRC) energy performance label.

The NFRC operates a program that tests, certifies, and labels windows and doors based on a series of performance ratings. Although this window label is a reliable way to compare different windows’ performance, it’s not the only thing you should consider when purchasing new windows or doors for your home!

The window experts at Quality Window & Door are firm believers in educating customers to help select the best product for your style, needs, and budget. Here, we break down the different elements of a window’s sticker, what they mean for performance, and other important factors to consider when purchasing new windows and doors for your home.

What Do the Numbers on a NFRC Window Label Mean?


A U-value is the measurement of a window’s rate of heat transfer. This tells homeowners how well a product will be able to provide insulation and keep heat from escaping out. The ratings range from 0.25 to 1.25.

NFRC label on an Infinity from Marvin Window

A lower U-value means less heat loss and better insulation.

Is U-value important when selecting a window?

The answer depends on what you’re looking for and the climate you live in. For climates with extreme heat or cold, looking for high-quality windows with a very low U-value could save you money on heating costs in the long run. This resource from ENERGY STAR provides recommended U-values based on your climate. For the DC, Maryland, and Virginia area, an ENERGY STAR qualified window must have a U-value of 0.30 or less.

Solar Heat Gain Coefficient (SHGC)

Solar heat gain coefficient (SHGC) measures how well the window’s blocks the heat from sunlight. Basically, it’s the reason you should keep your blinds closed and shades drawn to keep your house cool on a hot summer day. Technically speaking, the SHGC is a fraction that measures how much solar radiation is admitted through a window versus how much heat gain is blocked. Solar heat gain coefficient ranges between 0 and 1; a lower SHGC means less solar heat is transmitted to your house. For the DC, Maryland, and Virginia area, an ENERGY STAR qualified window must have a SHGC of 0.40 or less.

Is a low SHGC better?

It depends on a lot of factors, but one key factor is the orientation of the windows in your house. For west-facing windows that receive direct sunlight throughout the afternoon, less solar heat gain (a low SHGC) is generally a good thing to look for. But on south-facing walls, a higher solar heat gain coefficient could help naturally heat a home during the colder months.

Visible Transmittance (VT)

A NFRC energy performance label’s visible transmittance (VT) number measures how well a product is designed to pass daylight through to light your home. A higher VT means more natural light is allowed in through a window. A higher VT can reduce the need for artificial lighting. A window’s visible transmittance must be weighed against other factors to determine the best number for your home; more efficient windows sometimes have a lower visible transmittance value. For example, a triple-paned window is extremely energy efficient, but sunlight must pass through three panes of glass before reaching your home, which can make your home seem less bright.

What does visible transmittance mean for you?

The VT you should look for depends on your home’s lighting requirements, need to reduce interior glare, and whether you value natural lighting above other factors. Maximizing a window’s VT while also balancing the optimal u-value and SHGC can be a challenge, so all three factors must be considered together based on your priorities.

How Is the ENERGY STAR® label different from the NFRC label?

Both of these labels can be a great resource for window shoppers, but they are not the same thing. The ENERGY STAR label is part of a program from the U.S. Department of Energy that is used to designate a product as energy efficient. ENERGY STAR qualifications designate a window or door as energy efficient, and are based only off U-Factor and SHGC. The NFRC label helps you to compare the actual performances of energy-efficient windows based on several categories.

Most Important Factors When Choosing a Window

It can be easy to just look at the numbers on a label when comparing different windows in a showroom, but the rules for determine “the best window” can depend on a wide variety of factors you and your local window company should consider together. When conducting research on windows and doors for your home, you must first understand what your application is. From there, that will help guide you to choosing the best materials are best to fit your application and your budget.

Each material, whether it’s wood, vinyl, fiberglass, aluminum, or another, has its own benefits and features to consider—and efficiency ratings are only a part of that decision. You should look at how a product is made along with what materials it is made out of.

Longevity and durability often get overlooked in the window and door buying process, but think of it this way: Would you rather have a beautiful, durable window that matches your home’s style or save a small amount of money on your utility bill? When choosing the best window for your application, don’t pay so much attention to the numbers on the stickers that you overlook its craftsmanship, aesthetic value, and durability.

Educating yourself will help determine what window is best for your application, and your local window and door provider can help you understand materials, their combinations and differences, pros and cons.

At Quality Window and Door, we are always focused on choosing the best product for your operational need, budget, and aesthetic. Call us today or visit our showrooms in Maryland and Virginia to start your window buying journey!

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