Modern windows are designed to do far more than provide a view. In 2026, energy performance ratings play a critical role in helping homeowners compare windows based on how effectively they conserve energy, manage heat, and control light transmission. These ratings allow consumers to make informed decisions that can improve comfort, reduce energy costs, and support long-term efficiency goals.
Who Sets Window Energy Ratings?
Window energy performance ratings are established by the National Fenestration Rating Council (NFRC), an independent, non-profit organization. The NFRC’s role is to create standardized, objective methods for measuring the energy efficiency of windows, doors, and skylights.
The NFRC does not manufacture, sell, or endorse products. It does not recommend brands, and it has no affiliation with local building departments, contractors, or building codes. Its sole purpose is to ensure that performance ratings are consistent, transparent, and comparable across manufacturers.
NFRC ratings provide standardized data that explains how a window affects heat transfer, sunlight penetration, and air movement within a building.
NFRC Labels and Energy Star® in 2026
In 2026, NFRC labels continue to appear on all Energy Star®–certified windows, doors, and skylights. These labels display key performance metrics such as U-factor and Solar Heat Gain Coefficient (SHGC), allowing homeowners to compare products quickly and accurately.
Energy Star® requirements have become more climate-specific over time, meaning recommended performance thresholds vary based on geographic region. NFRC ratings remain the foundation for determining whether a product meets those regional standards.
U-Factor: Measuring Heat Transfer
The U-factor measures how quickly heat moves through a window, door, or skylight. Unlike glass-only measurements, the NFRC U-factor applies to the entire unit, including:
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Glass
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Frame
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Spacers
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Seals
In 2026, typical U-factor values for residential windows generally range from 0.25 to 1.25, with lower numbers indicating better insulation performance.
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Lower U-factor = less heat loss in winter and less heat gain in summer
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Higher U-factor = more heat transfer and lower energy efficiency
The ideal U-factor depends on climate. Colder regions benefit most from very low U-factors, while warmer climates may prioritize other performance metrics alongside insulation.
Solar Heat Gain Coefficient (SHGC)
The Solar Heat Gain Coefficient (SHGC) indicates how much solar heat passes through a window and enters the building. It is expressed as a number between 0 and 1.
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Lower SHGC values reduce heat gain from sunlight, helping keep homes cooler in hot or sunny climates
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Higher SHGC values allow more solar heat inside, which can be beneficial in colder climates during winter
Choosing the right SHGC depends on several factors, including:
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Local climate
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Window orientation (north, south, east, west)
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Shading from trees, buildings, or overhangs
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Heating vs. cooling priorities
In 2026, advanced glazing coatings allow manufacturers to fine-tune SHGC without significantly reducing visible light.
Additional Window Energy Ratings
Air Leakage (AL)
Many windows also list an air leakage rating, which measures how much air passes through the window assembly—not through the glass, but around the frame.
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Measured in cubic feet per minute per square foot (cfm/ft²)
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Lower numbers indicate better sealing and reduced drafts
Improved air sealing helps maintain indoor temperatures, improves comfort, and reduces heating and cooling demand.
Visible Transmittance (VT)
Visible Transmittance (VT) measures how much visible light passes through the window glass.
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Values range from 0 to 1
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Higher VT = more natural daylight
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Lower VT = less glare and more light control
In 2026, homeowners often balance VT with SHGC to achieve bright interiors without excessive heat gain, especially in sun-exposed rooms.
Why These Ratings Matter More Than Ever
As energy costs continue to fluctuate and efficiency standards evolve, understanding window performance ratings is increasingly important. NFRC ratings allow homeowners to compare products objectively, optimize comfort for their climate, and make long-term investments that reduce energy use.
By reviewing U-factor, SHGC, air leakage, and visible transmittance together, homeowners can choose windows that align with their regional climate, home design, and energy-efficiency goals—making window upgrades smarter and more effective in 2026 and beyond.
