An NFRC window label helps you compare the energy performance of different windows before you buy. By understanding the U-factor, Solar Heat Gain Coefficient (SHGC), visible transmittance (VT), air leakage and condensation resistance ratings, you can choose windows that better match your home's climate, daylight needs and comfort goals.

At The Window Depot, with stores in Tucson, Phoenix, Chandler, Surprise, El Paso, Albuquerque and National City, we help homeowners, contractors and remodelers understand window performance when comparing vinyl replacement windows. The National Fenestration Rating Council (NFRC) label provides standardized performance information, making it easier to compare certified products instead of relying on appearance or general product descriptions alone. The ratings are especially useful when two windows look similar but have different glass packages or energy performance characteristics.

What Is an NFRC Window Label?

An NFRC window label is a product label that displays standardized ratings for a window's energy and related performance. NFRC, the National Fenestration Rating Council, is an independent, nonprofit organization that certifies the performance ratings of windows, doors and skylights.

The label helps explain how a window manages heat transfer, sunlight and daylight. Depending on the product and its certification, it may also display additional performance ratings, such as air leakage and condensation resistance.

NFRC ratings are determined through standardized procedures involving computer simulations and physical testing. This allows homeowners and building professionals to compare products using consistent measurement methods. The ratings describe the tested product under specified conditions, so they should be used alongside information about the window's construction, installation requirements and suitability for the project.

You can also use the NFRC Certified Products Directory to look up certified products and compare available ratings.

Why Should You Read an NFRC Window Label Before Buying?

Reading the label helps you understand what a window is designed to do rather than assuming that every energy-efficient window performs the same way.

For example, a window with a low U-factor may provide good resistance to heat transfer, but that number does not tell you how much sunlight or solar heat enters through the glass. Those details are covered by SHGC and VT.

Likewise, a window with a favorable insulation rating may still have a different air leakage rating from another product. Each measurement answers a separate question about performance.

Understanding the label can help you:

• Compare the energy performance of different window products.
• Evaluate how much solar heat may enter your home.
• Determine how much natural daylight a window transmits.
• Compare available air leakage and condensation resistance ratings.
• Identify which ratings matter most for your climate and room orientation.

The goal is not to find the lowest number in every category. Some ratings are better when lower, while others are better when higher. The right combination depends on your home's needs.

How Do You Read the Main Ratings on an NFRC Window Label?

Start by locating the energy performance ratings, which commonly include U-factor and SHGC. Then review the additional performance ratings, if provided, such as VT, air leakage and condensation resistance.

Here is a quick reference to what each rating means.

Not every label displays every additional rating. Check the information available for the specific window you are considering, and do not assume that an unlisted rating has a particular value.

What Does U-Factor Mean on a Window Label?

U-factor measures how readily heat transfers through a window. A lower U-factor means the window provides greater resistance to heat transfer, which can help reduce unwanted heat loss or gain through the window assembly.

This rating matters in both heating and cooling climates. In colder conditions, a lower U-factor helps reduce heat escaping from the home. In warmer climates, it can help limit heat transfer from hot outdoor conditions into cooler indoor spaces.

U-factor is not the same as SHGC. U-factor concerns heat transfer through the window, while SHGC focuses specifically on solar heat entering through the glass and other parts of the product.

Is a lower U-factor always better?

A lower U-factor generally indicates better insulating performance, but it should not be the only factor in your decision. The window also needs to suit your climate, glass requirements, frame material and budget.

When comparing two products, make sure you are reviewing the ratings for the actual window configurations you plan to purchase. Glass options and product construction can affect performance.

For homes in hot climates, it is particularly useful to review U-factor alongside SHGC. A window needs to manage both heat transfer and the effects of direct sunlight.

What Is Solar Heat Gain Coefficient (SHGC)?

Solar Heat Gain Coefficient measures the fraction of incoming solar energy that a window allows into the home. It is expressed as a number between 0 and 1. A lower SHGC means less solar heat enters, while a higher SHGC means more solar heat passes through.

This rating is especially important in sunny locations such as Tucson, Phoenix, Chandler, Surprise and El Paso, where windows may receive strong sunlight for much of the year.

A lower SHGC can help reduce unwanted solar heat gain and the cooling demand associated with it. However, the ideal value depends on the climate, window orientation, shading and how the room is used.

For example, a west-facing window exposed to intense afternoon sunlight may benefit from a lower SHGC. A shaded window may have different requirements.

Should you choose the lowest SHGC available?

Not automatically. A lower SHGC can be beneficial when reducing solar heat is a priority, but the best selection depends on the home's overall design and climate.

Review SHGC alongside U-factor and VT. Solar-control Low-E coatings are a common way to lower SHGC, and our guide to Low-E glass explains how they work.

 A window that limits solar heat while still allowing useful daylight may be a better fit than one selected using only a single rating.

The guide to energy-efficient windows for hot climates explains how to evaluate window performance in warm, sunny environments.

What Does Visible Transmittance (VT) Mean?

Visible transmittance measures how much visible daylight passes through a window. The rating ranges from 0 to 1, with a higher number indicating that more visible light passes through the product.

VT is useful when you want to balance natural light with glare control and solar heat management. A higher VT may help brighten a room, while a lower VT may be appropriate when limiting brightness is a priority.

However, VT does not measure the window's overall energy efficiency. It measures visible light transmission, not insulation or solar heat gain.

Two windows with similar U-factors and SHGC values may have different VT ratings because of their glass coatings, tint and other design features.

What is a good VT rating for windows?

There is no single VT value that works best for every home. Department of Energy guidance notes that VT for actual window products ranges from about 0.10 to 0.80, and that values below 0.50 noticeably reduce the light coming through.

Rooms that need more natural daylight may benefit from a higher VT. Rooms with intense direct sunlight or troublesome glare may require a different balance.

For a more detailed explanation, read our guide to visible transmittance (VT) for windows and what makes a good rating.

What Is Air Leakage on an NFRC Window Label?

Air leakage measures how much air passes through a window assembly under standardized testing conditions. It is commonly expressed in cubic feet per minute per square foot of window area (cfm/ft²).

A lower air leakage rating indicates that less air passed through the tested window during the test. This can be relevant when you want to reduce drafts and improve indoor comfort.

ENERGY STAR consumer guidance identifies 0.30 cfm/ft² as a common benchmark used in industry standards and building codes. It is a useful reference point, not a guarantee that every product below that number will perform identically in every installed situation.

Air leakage is also different from U-factor. U-factor describes heat transfer, while air leakage measures air movement through the window assembly.

Can a window with a good air leakage rating still feel drafty?

Yes. The NFRC rating describes the window product under standardized testing conditions, not the quality of the entire installed opening.

Drafts can occur when the window is not properly sealed to the wall, when installation gaps remain, or when weatherstripping and other components are damaged. These problems can affect comfort even if the window itself has a favorable air leakage rating.

When comparing products, check the certified air leakage rating where available. For more information, read our article on window air leakage ratings and what makes a good number.

What Is Condensation Resistance on a Window Label?

Condensation resistance describes how well a window resists moisture forming on its interior surfaces under the conditions used to determine the rating.

The traditional NFRC Condensation Resistance rating uses a scale from 1 to 100. A higher score indicates greater resistance to condensation. Availability and labeling may vary as NFRC updates its rating procedures, so check which condensation rating system applies to the product you are reviewing.

Condensation can develop when warm, moist indoor air meets a sufficiently cold surface. Window glass, frame areas and the edges of insulated glass units can all be potential locations for moisture to form.

A window with better condensation resistance may help reduce moisture buildup on interior surfaces. However, condensation also depends on indoor humidity, outdoor temperature, ventilation and other building conditions.

Does a higher condensation resistance rating mean condensation cannot occur?

No. A higher rating indicates better resistance under the applicable test conditions, but it does not guarantee that condensation will never appear.

High indoor humidity or very cold weather can still contribute to condensation. If moisture repeatedly forms around windows, consider indoor humidity levels, ventilation and the condition of the window and surrounding installation.

This rating is useful when comparing products, particularly where condensation is a recurring concern, but it should be considered alongside the other performance measurements.

How Do You Compare All Five NFRC Window Ratings?

The easiest way to compare windows is to review the ratings together instead of treating any one number as a complete measure of quality.

Consider a homeowner comparing two hypothetical windows:

These figures are illustrative examples only, not verified ratings for products sold by The Window Depot.

In this example, Window A has a lower U-factor, SHGC and air leakage value, along with a higher condensation resistance score. Window B has a higher VT, meaning it transmits more visible daylight.

Which window is the better choice? It depends on the homeowner's priorities. If reducing solar heat and air leakage is the main goal, Window A may be worth closer consideration. If allowing more visible daylight is important, Window B may offer an advantage.

The comparison also assumes that the products are being evaluated under comparable rating systems and units. Always verify the actual certified ratings before making a purchase.

How Should You Choose NFRC Window Ratings for Your Climate?

Your climate and the direction a window faces can affect which ratings deserve the most attention.

For hot, sunny climates

In areas such as Tucson and Phoenix, limiting unwanted solar heat gain is often a major consideration. Pay close attention to SHGC, while also checking U-factor and VT. A lower SHGC can help limit solar heat entering through sun-exposed windows, while VT helps you understand how much daylight the glass transmits.

Exterior shade, overhangs and other design features also influence how much sunlight reaches a window.

For colder climates

U-factor deserves particular attention because a lower value indicates greater resistance to heat transfer. Condensation resistance can also be helpful when evaluating how a window may perform under conditions that encourage moisture to form on interior surfaces.

The appropriate SHGC depends on the building design, orientation and whether solar heat gain is desirable or needs to be limited.

For rooms with strong sunlight or glare

Review SHGC and VT together. SHGC tells you about solar heat entering the home, while VT indicates visible light transmission. These measurements are related to different aspects of sunlight, so neither can substitute for the other.

Shading and window placement can also help manage glare without relying entirely on the glass rating.

For rooms where drafts are a concern

Check air leakage ratings when they are available. Also evaluate installation quality, frame condition and weatherstripping, because the product rating alone cannot identify every source of drafts in an existing home.

Does an NFRC Label Tell You Whether a Window Is ENERGY STAR Certified?

An NFRC label provides certified performance ratings that can be used to evaluate windows. ENERGY STAR qualification is a separate designation based on applicable program requirements.

ENERGY STAR consumer guidance identifies U-factor and SHGC as the primary window performance ratings used for qualification. The applicable limits depend on the program's requirements and the relevant climate criteria.

Do not assume that a window qualifies for ENERGY STAR simply because it has an NFRC label or performs well in one category. Verify the product's current qualification and applicable requirements if ENERGY STAR certification is important to your project.

The NFRC label remains useful even when you are comparing products that do not carry the ENERGY STAR designation, because it gives you standardized performance information.

Where Can You Find and Verify NFRC Window Ratings?

Start with the NFRC label attached to the window or provided in its product documentation. Check the listed ratings and confirm that the information corresponds to the exact product and glass configuration you are considering.

You can also search the NFRC Certified Products Directory to look up certified product lines and available performance data.

When reviewing the information, check the following:

• Product identification: Make sure the label matches the window you intend to buy.
• U-factor and SHGC: Compare heat transfer and solar heat gain.
• VT: Check how much visible daylight passes through.
• Additional ratings: Review air leakage and condensation resistance when listed.
• Product configuration: Confirm the ratings apply to the specific product and options being considered.

Remember that ratings describe performance under standardized conditions. Actual results also depend on proper installation, the building envelope, shading and indoor conditions. Contractors submitting window specs for permits or energy compliance should pull the certified ratings for the exact configuration being ordered, not the best numbers in the product line.

What Are the Most Common Mistakes When Reading an NFRC Window Label?

Several common mistakes can lead to a poor comparison between window products.

Choosing a window based on one rating alone. A low U-factor does not tell you how much solar heat enters or how much daylight passes through. Review the ratings together.

Assuming lower is always better. Lower values are generally favorable for U-factor, SHGC when reducing solar heat is the goal, and air leakage. VT and condensation resistance generally favor higher values when more daylight and greater resistance to condensation are desired.

Confusing VT with SHGC. VT measures visible daylight, while SHGC measures the fraction of solar energy entering through the window. A window can have different results for these two ratings.

Ignoring installation quality. Even a well-rated window can have comfort problems if the surrounding opening is poorly sealed or installed incorrectly.

Comparing different configurations without checking the details. Glass packages and product designs can change performance. Make sure the ratings apply to the actual windows you are evaluating.

Assuming every label lists every rating. Additional ratings may not appear on every product label. Verify available information rather than treating a missing value as a particular score.

Frequently Asked Questions About NFRC Window Labels

What does NFRC stand for?

NFRC stands for the National Fenestration Rating Council. It is an independent, nonprofit organization that certifies standardized energy performance ratings for windows, doors and skylights.

Which NFRC window rating is the most important?

There is no single most important rating for every home. U-factor, SHGC, VT, air leakage and condensation resistance measure different aspects of performance. The most relevant combination depends on your climate, window orientation and comfort priorities.

Is a lower U-factor better for windows?

Yes. A lower U-factor indicates that a window resists heat transfer more effectively. However, you should also review SHGC and the other available ratings before choosing a product.

What is a good SHGC rating for a window?

The right SHGC depends on the climate and the amount of solar heat you want to admit. Lower values allow less solar heat through, which can be helpful in hot, sunny conditions. The ideal rating depends on the complete building design.

Is a higher VT rating better?

A higher VT means more visible daylight passes through the window. It may be helpful in rooms where daylight is a priority, although glare control and solar heat gain should also be considered.

What is a good air leakage rating for windows?

A lower air leakage rating means less air passed through the tested window. A value of 0.30 cfm/ft² or less is a commonly cited benchmark, but you should verify the requirements applicable to your project and the exact product.

What does a condensation resistance score of 60 mean?

Under the traditional NFRC Condensation Resistance scale, a score of 60 indicates the product's relative resistance to condensation on a scale from 1 to 100. A higher score indicates greater resistance under the rating method. It does not guarantee that condensation will never occur.

Can I use the NFRC label to compare vinyl windows?

Yes. NFRC ratings can help you compare certified vinyl window products using standardized performance measurements. Check the ratings for the exact product and glass configuration, rather than relying on frame material alone.

Compare NFRC Window Ratings at The Window Depot

Understanding an NFRC window label makes it easier to evaluate window performance before making a purchase. U-factor explains heat transfer, SHGC measures solar heat gain, VT describes visible daylight, air leakage measures air movement through the product, and condensation resistance indicates how well the window resists moisture buildup on interior surfaces.

At The Window Depot, homeowners, contractors and remodelers can use these measurements as a starting point when comparing available window options. Consider your climate, the direction each window faces and the way you use each room before deciding which ratings matter most.

Browse our vinyl windows online or visit a The Window Depot location in Tucson, Phoenix, Chandler, Surprise, El Paso, Albuquerque or National City to discuss available options. You can also use our store locator to find a nearby location.