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.

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. — Source: ASHRAE Standard 169 / IECC Table R301.1

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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.

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    <img src="https://remodelcalculators.com/api/figure-embed/climate-zone-county-assignment" alt="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." width="800" height="470" style="width:100%;height:auto;border:0" loading="lazy">
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