Window Energy Ratings in the US: NFRC Label and ENERGY STAR

In the United States, a window's energy rating is the set of numbers on its NFRC label, mainly the U-factor and the solar heat gain coefficient (SHGC). There is no single letter grade. To judge whether a rating is good, check it against the current ENERGY STAR criteria (Version 7.0) for your climate zone. The U-factor must be 0.22 or lower in the Northern zone, 0.25 in North-Central, 0.28 in South-Central and 0.32 in the Southern zone, with an SHGC limit for each zone. A lower U-factor is better everywhere. The right SHGC depends on your climate.

Updated: October 2026.

The NFRC label

The National Fenestration Rating Council (NFRC) describes itself as an independent, nonprofit certification body for the energy performance of windows, doors and skylights. Its ratings come from computer simulation and physical testing, and each certification involves a laboratory and an inspection agency. NFRC U-factor ratings cover the whole product, including the frame and spacer, not just the glass.

According to NFRC's consumer guide, U-factor, SHGC and visible transmittance are mandatory ratings on the label. Air leakage and condensation resistance are optional. The label also states that NFRC ratings are determined for a fixed set of environmental conditions and a specific product size, and that NFRC does not recommend any product.

ENERGY STAR Version 7.0 criteria for windows

ENERGY STAR is run by the US Environmental Protection Agency (EPA). Version 7.0 of the specification for residential windows, doors and skylights took effect on October 23, 2023. A window qualifies only if it has NFRC-certified U-factor and SHGC ratings that meet the limits for a climate zone. It also needs certification from a body that EPA recognizes.

Other Version 7.0 requirements:

• Air leakage: windows, sliding doors and skylights must be at or below 0.3 cfm/ft², and swinging doors at or below 0.5 cfm/ft². The product shows this with "≤ 0.3" (or "≤ 0.5") in the air leakage field of the NFRC label, or with one of the certification labels EPA lists, such as the AAMA Gold Label or the WDMA Hallmark label.
• Equivalent energy performance applies only to windows in the Northern zone. It lets a window with a slightly higher U-factor qualify if its SHGC is high enough to collect more winter sun.
• Doors are rated by glazing level (opaque, ½-lite or less, more than ½-lite) instead of by zone alone. Skylights must have a U-factor of 0.45 or lower in the Northern zone and 0.50 or lower elsewhere, with SHGC 0.25 or lower outside the Northern zone.
• Test methods: NFRC 100 for U-factor and NFRC 200 for SHGC. U-factor is recertified every 5 years and air leakage every 10 years.

Find your climate zone

ENERGY STAR assigns climate zones by state and county, and in some places by ZIP code. Use the ENERGY STAR climate zone finder or the climate zone map.

Example: reading a label against the criteria

The sample NFRC label in the US Department of Energy's training material shows a U-factor of 0.30, an SHGC of 0.30, a VT of 0.51, air leakage of 0.2 and condensation resistance of 51. Compared with the Version 7.0 table:

• U-factor 0.30 is within the Southern limit (≤ 0.32) but above the Northern, North-Central and South-Central limits.
• SHGC 0.30 is above the Southern and South-Central limit (≤ 0.23).
• Air leakage 0.2 is within the 0.3 cfm/ft² limit.

The air leakage passes, but a window with these ratings would not meet Version 7.0 in any zone.

How to use the GlassBase calculator with these numbers

1. Look up your ENERGY STAR climate zone and note the U-factor and SHGC limits from the table above.
2. Open the window energy calculator, enter your ZIP code and set the material, profile system, glazing and spacer.
3. Read the calculated U-factor (shown in the same Btu/(h·ft²·°F) units as the NFRC label) and SHGC, and compare them with your zone's limits.
4. Change one option at a time, such as glazing or window facing, and watch how heating and cooling savings shift. A low SHGC reduces summer cooling loads and a high one collects more winter solar heat; the calculator shows which effect is larger for your ZIP code and wall direction.
5. Before you buy, confirm the actual product's certified ratings on its NFRC label, in the NFRC Certified Products Directory and in the ENERGY STAR Product Finder. The calculator uses ISO 10077-1 methods, so its values are estimates, not NFRC ratings. See how the calculator works.

To find companies that make or install windows near you, see How to find a window manufacturer in the US or browse window companies by city. Definitions of the terms on this page are in the glossary.

Sources

• US EPA, ENERGY STAR, Residential Windows, Doors, and Skylights Eligibility Criteria, Version 7.0 (Tables 1–6; effective date October 23, 2023)
• US EPA, ENERGY STAR, Key product criteria and certification criteria table for windows (Oct 2023)
• US EPA, ENERGY STAR, Independently tested and certified energy performance (rating ranges and scales)
• NFRC, nfrc.org and Residential product certification
• NFRC consumer guide, Window ratings (mandatory and optional ratings)
• US DOE, Building Science Education, Fenestration – Define Key Terms (definitions and sample NFRC label)