What it does or measures
The short answer
The NFRC label can report U-factor, solar heat gain coefficient, visible transmittance, air leakage, and condensation resistance for a rated product configuration.
How to compare it
- Match the label to the exact product, size, operation, frame, and glass configuration quoted.
- Read each metric separately; a lower or higher value is not universally better across every metric and climate goal.
- Use ENERGY STAR criteria as a separate climate-based certification check.
Limitations to keep in view
- A product rating does not predict an individual home's bill, comfort, installation quality, or water management.
- Labels for different configurations should not be treated as interchangeable.
Climate and use context
- Climate and project priorities affect how U-factor and solar heat gain should be interpreted.
Sources
Sources
- Window Energy Performance Ratings — National Fenestration Rating Council
- What Makes a Product ENERGY STAR — ENERGY STAR