Window Energy Ratings: U-Factor, SHGC & NFRC Labels
Window labels are useful when you know which numbers answer which question. California code materials rely on standardized procedures for U-factor and solar heat gain coefficient, which makes product comparisons more meaningful.
Call with your rough window count, current problem, and project goals.
Call 714-710-4946U-factor
Measures heat transfer through the window assembly. Lower generally means less heat transfer.
SHGC
Solar heat gain coefficient describes the fraction of solar radiation admitted through the product. Lower values mean less solar heat gain.
Visible transmittance
VT describes how much visible light passes through. It can help compare daylight characteristics, although tint, coatings and glass area also affect the experience.
Use current code requirements
The California Energy Code changes over time. For permitted work, verify the standards applicable to the project and permit date. Official California Energy Commission materials should take priority over old blog posts or generic national advice. See California Energy Commission resources.
Frequently asked questions
Is a lower U-factor better?
For heat transfer, a lower U-factor generally indicates better insulating performance.
Is a lower SHGC always better?
Not in every design context. SHGC should be evaluated with climate, orientation, shading and code requirements.
What is an NFRC label?
NFRC labels provide standardized ratings for fenestration products so consumers and code professionals can compare performance.