In 2025, the U.S. Department of Energy reported that energy-efficient windows can cut heating and cooling costs by up to 30%, but only if you know how to read and compare their energy performance ratings. Choosing NFRC-certified products is more important than ever for lowering bills, improving comfort, and unlocking up to $1,200 in federal tax credits.

A father and son working together on an older home with a deteriorating window frame.
Upgrading old windows to NFRC-certified products can significantly improve energy efficiency and comfort for your home.

The National Fenestration Rating Council (NFRC), an independent nonprofit, certifies the performance of windows, doors, and skylights through a uniform rating system recognized nationwide. This guide breaks down how NFRC ratings work, why they matter, and how they can help Pennsylvania homeowners choose the best energy-efficient windows for their climate zone.

What Is the NFRC?

The National Fenestration Rating Council is a third-party, nonprofit organization that:

  • Administers the only uniform rating system for windows, doors, and skylights in the U.S.
  • Works with government agencies, manufacturers, and the Efficient Windows Collaborative to promote accurate product information.
  • Provides fair, credible, and independently tested energy performance ratings so consumers can compare products with confidence.

These performance ratings are not estimates; they are based on rigorous, scientifically validated methods to ensure accuracy.

Two professional industrial workers are taking precise measurements on a window.
NFRC performance ratings are based on rigorous, scientifically validated methods to ensure the accuracy of a product’s performance.

How the NFRC Label Helps Homeowners

The NFRC label is your tool for comparing products based on tested energy performance. It:

  • Appears on all ENERGY STAR® qualified windows, doors, and skylights.
  • Includes ratings for U-Factor, Solar Heat Gain Coefficient (SHGC), Air Leakage (AL), Visible Transmittance (VT), and Condensation Resistance.
  • Reflects the performance of the entire unit, not just the glass.

In short, the NFRC label helps you make informed decisions that lead to lower energy bills, better comfort, and long-term value.

Understanding NFRC Performance Ratings

U-Factor

  • Measures heat transfer, how well a window retains warmth.
  • Values typically range from 0.20 to 1.20.
  • Lower numbers mean better insulation and less heat flow.

Solar Heat Gain Coefficient (SHGC)

  • Measures how much solar heat from solar radiation passes through.
  • A low heat gain coefficient SHGC allows less solar heat, keeping interiors cooler in summer.
  • Higher values can be beneficial in colder climates to help capture winter warmth.

Air Leakage (AL)

  • Measures how much air enters through the product.
  • Lower air leakage means fewer drafts, less air leakage, and improved comfort.

Visible Transmittance (VT)

  • Measures how much visible light enters your home.
  • Higher values mean more natural light and less reliance on artificial lighting.

Condensation Resistance

  • Measures how well a product resists condensation.
  • Higher numbers mean better performance against moisture buildup and related issues.

NFRC Certification Process & Codes Compliance

NFRC-certified products are independently tested by accredited labs through a multi-step certification process:

  1. Initial design review.
  2. Testing for U-Factor, SHGC, Air Leakage, Visible Transmittance, and Condensation Resistance.
  3. Ongoing quality checks and recertification.

Building Codes vs. Energy Codes Compliance

In Pennsylvania, residential windows must meet both building codes and energy codes. Building codes focus on overall safety, structural integrity, and proper installation practices. Energy codes like the 2018 International Energy Conservation Code (IECC) with state amendments, address the efficiency and performance of the windows themselves.

For windows, this means:

  • U-Factor: Maximum 0.32 (lower numbers mean better insulation)
  • Solar Heat Gain Coefficient (SHGC): Maximum 0.40 for most climate zones in the state
  • Air Leakage: Must not exceed 0.3 cfm/ft²

Meeting these standards satisfies local codes and can qualify homeowners for federal tax credits and state or utility rebates. The Efficient Windows Collaborative and the Pennsylvania Department of Environmental Protection recommend windows that retain heat in winter and limit solar gain in summer, especially in Pennsylvania areas like Pottstown, King of Prussia, Quakertown, Lansdale, West Chester, Downingtown, and Reading.

Choosing Energy Efficient Windows, Doors, and Skylights

Reading the NFRC Label

Learn to interpret each category: U-Factor, SHGC, Air Leakage AL, Visible Transmittance, and Condensation Resistance to compare products effectively.

Matching to Your Climate Zone

Use the Window Selection Tool and NFRC resources to choose windows suited to your climate and home orientation. For example, colder areas may need low U-Factor windows for heat retention, while mixed climates benefit from balanced U-Factor and SHGC. South-facing windows often need a lower SHGC to limit summer heat gain.

NFRC Website & Resources

The NFRC website offers certified product directories, performance data, and educational materials to help homeowners choose energy-efficient products across multiple categories.

NFRC in Pennsylvania Homes

For homeowners in Pennsylvania, rebates and incentives are often tied to NFRC-certified and ENERGY STAR label products. Local climates require careful balance; windows that allow more light in winter but limit solar heat gain in summer are ideal.

Keystone Window of Pennsylvania’s Commitment to NFRC Standards

At Keystone Window of Pennsylvania:

  • All products are NFRC-certified products that meet strict thermal efficiency guidelines.
  • Every window carries the ENERGY STAR label (certification is required for eligibility).
  • The NFRC label on Keystone products reflects the tested performance of the entire unit, ensuring less air leakage and compliance with Pennsylvania building codes.

Take Action for Better Energy Efficiency

NFRC ratings provide reliable, independently tested data to help you choose windows, doors, and skylights that truly perform. Selecting NFRC-certified and ENERGY STAR® products can lower your energy bills, improve year-round comfort, and help you meet energy codes, while also qualifying for tax credits and rebates.

Find the Best Energy-Efficient Windows for Your Home

Contact Keystone today to explore certified window options tailored to your home and climate zone. When performance, comfort, and savings matter, let NFRC certification be your standard for choosing the best energy-efficient windows.