Why IECC climate zones are assigned by county, not by state or city
IECC zones are assigned county-by-county (ASHRAE 169), so one state can span two or three zones. The calculator resolves your ZIP to a county, and the county sets your zone.
What this diagram shows
A schematic state drawn as a grid of counties, each tinted on the climate ramp and stamped with its IECC zone number — showing zones 4, 5, and 6 all within one state. One county is highlighted as “your county.” A side panel shows the lookup the calculator runs: you enter a ZIP code, it resolves to a county, and the county sets the IECC climate zone. Because zones are assigned county-by-county under ASHRAE Standard 169, two towns in the same state can fall in different zones, so the calculator matches your exact county rather than your city.
Climate Zone Calculator
Find your IECC climate zone by ZIP code or county, plus the code-required insulation R-values and window U-factors for your zone. Free, no signup.
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