The short answer
U-factor describes heat transfer through the complete rated product, while solar heat gain coefficient describes the fraction of incident solar heat admitted. Lower is not automatically the right answer for every metric and project; climate, orientation, shading, daylight, and comfort goals matter.
| Compare | U-factor | Solar heat gain coefficient |
|---|---|---|
| Primary meaning | Heat transfer through product | Admitted solar heat |
| Selection context | Climate and heat-loss goals | Climate, orientation, shade, and cooling or passive-gain goals |
Sources
Sources
- Window Energy Performance Ratings — National Fenestration Rating Council
- Residential Windows, Doors, and Skylights — ENERGY STAR
- What Makes a Product ENERGY STAR — ENERGY STAR