ENERGY STAR & IECC window U-factor & SHGC by climate zone
This is our own cross-zone reference and the moat behind the site. For every US climate zone it gives the LABELED ENERGY STAR 7.0 maximum window U-factor and SHGC next to the LABELED IECC 2021 code minimum, so you can see at a glance that ENERGY STAR is stricter than the code floor. It is a dated snapshot of published criteria, not a live feed. See how it’s derived in the methodology, and use it with the ENERGY STAR climate-zone checker and the U-factor ↔ R-value converter.
| Climate zone (ENERGY STAR) | ENERGY STAR max U | ENERGY STAR SHGC | IECC zone | IECC max U | IECC SHGC |
|---|---|---|---|---|---|
| Northern | 0.22 | ≥ 0.17 (any) | 6 | 0.30 | NR |
| North-Central | 0.25 | ≤ 0.40 | 5 | 0.30 | NR |
| South-Central | 0.28 | ≤ 0.23 | 3 | 0.30 | ≤ 0.25 |
| Southern | 0.32 | ≤ 0.23 | 2 | 0.40 | ≤ 0.25 |
LABELED published snapshots — ENERGY STAR 7.0 residential window criteria and IECC 2021 fenestration limits (U-factor in BTU/hr·ft²·°F; SHGC 0–1; NR = no requirement). ENERGY STAR is stricter than the IECC code floor. The IECC zone shown is a representative mapping — confirm your exact IECC climate zone, the current ENERGY STAR criteria, your local energy code and the product’s NFRC-rated numbers. Snapshot: 2026-07-11.