The short answer
An NFRC label reports standardized performance for a specific product configuration. Match it to the exact window quoted, then interpret U-factor, solar heat gain coefficient, visible transmittance, air leakage, and condensation resistance separately for the project's climate and goals.
- U-factor
- Rate of heat transfer; lower values indicate lower heat flow under the rating.
- SHGC
- Fraction of incident solar heat admitted; project priorities vary by climate and exposure.
- Visible transmittance
- Fraction of visible light transmitted.
- Air leakage
- Rated air passage through the product under test conditions.
- Condensation resistance
- Relative resistance to interior surface condensation under rating conditions when reported.
Sources
Sources
- Window Energy Performance Ratings — National Fenestration Rating Council
- What Makes a Product ENERGY STAR — ENERGY STAR