Glossary · Climate

IECC climate zone

Also called: climate zone · climate zones · IECC zone · IECC climate zones · DOE climate zone · moisture regime

The US energy code's climate map: zones 0 (hottest) to 8 (coldest), plus a moisture letter — A for moist, B for dry, C for marine.

What it means

The International Energy Conservation Code (IECC) assigns every US county a zone number, based mainly on heating and cooling degree days, and a moisture letter. The 2021 IECC adopted the ASHRAE 169-2013 map, which added a zone 0 (not found in the US) and moved about 400 counties, mostly to warmer zones. Energy codes and ENERGY STAR insulation advice are keyed to these zones.

Why it matters in an audit

Your zone sets recommended insulation levels, window criteria and airtightness targets, and signals whether you need a cold-climate heat pump.

Typical numbers

Reference values with their sources. Your auditor’s report gives the figure for your own house.

What	Value	Source
Zones and moisture regimes	Zones 0–8; A = moist, B = dry, C = marine (2021 IECC, based on ASHRAE 169-2013)	energycodes.gov ↗
Building America mapping	Cold = zones 5–6 (about 5,400–9,000 HDD, °F); very cold = zone 7 (9,000–12,600); subarctic = zone 8 (12,600 or more)	energy.gov ↗
Cold-climate heat pump scope (NEEP)	Zone 4 and colder	neep.org ↗

Sources

Learn more here

Related terms

Heating degree days (HDD) A measure of how cold a place is: each day adds how far its average temperature falls below 65°F. More degree days means more heating.
Cooling degree days (CDD) A measure of how hot a place is: each day adds how far its average temperature rises above 65°F. More degree days means more air conditioning.
R-value How well a material resists heat flow; higher is better, and insulation is rated with it, such as R-20 for walls or R-50 for attics.
ACH50 An airtightness score: how many times an hour the house's whole volume of air leaks out while a test fan pulls on it; lower means tighter.
Hot-humid climate A climate with long, hot, muggy summers, like the US Gulf Coast and Florida, where controlling humidity matters as much as temperature.
Marine climate A mild coastal climate with cool, wet winters and dry summers, like the US Pacific Northwest and coastal British Columbia.
Heating-dominated vs cooling-dominated climate Whether a place needs more energy for heating or for cooling over a year, which changes which upgrades and equipment matter most.
IECC (International Energy Conservation Code) The model US energy code for new homes and additions, updated about every three years; states and cities adopt an edition, often with changes.
PNNL (Pacific Northwest National Laboratory) A US Department of Energy national laboratory whose building research includes the Building America Solution Center and county climate zone data.
ASHRAE An international society of heating, cooling and ventilation engineers whose standards define things like commercial energy audit levels and climate zones.

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