US climate zone map
Type any US ZIP code to get your IECC climate zone, DOE Building America zone, heating and cooling degree days, design temperatures, and the R-value targets that apply to your house. The sizing, load, and rebate calculators on this site take climate zone as input.
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Map colors show the dominant IECC climate zone group (1-8) per state. A state can span two zones. Click any state to see the zone detail. ZIP lookup gives the precise zone including the moisture sub-zone (A humid, B dry, C marine).
What is a climate zone and why does it matter for HVAC?
A climate zone is a numbered region defined by the U.S. Department of Energy that bundles counties with similar heating and cooling demands. Zone 1 covers the warmest parts of the country, like Miami and Honolulu. Zone 8 covers the coldest, like interior Alaska. Every Manual J load calculation, every energy code, every federal rebate, and every HVAC sizing rule of thumb starts with the zone. Pick the wrong zone and you can end up with a furnace that runs at half load all winter or a heat pump that quits at the first cold snap.
There are actually three different zoning systems used by HVAC contractors and energy code officials, and they overlap but do not match exactly. The map and lookup above show you the IECC zone (used by building codes), the Building America zone (used by DOE residential research), and the design-temperature band (used by sizing software). Knowing which one matters for which decision saves a lot of confusion.
IECC climate zones: the building-code definition
The International Energy Conservation Code splits the country into eight numbered zones from 1 (hottest) to 8 (coldest), with a moisture sub-zone letter: A for humid, B for dry, and C for marine. Zone 4A is the mid-Atlantic. Zone 4B is the desert southwest interior. Zone 4C is the Pacific Northwest west of the Cascades. Same number, very different HVAC system selection.
State building codes adopt the IECC and then layer their own amendments on top. California uses Title 24, which is roughly IECC plus stricter envelope rules. Florida uses the FBC. Most other states follow IECC 2018 or IECC 2021 directly. When you pull a permit for a new HVAC system, the inspector checks against your IECC zone for the minimum SEER2, AFUE, HSPF2, and insulation R-values.
IECC climate zone reference table (all 8 zones)
Full reference for every IECC climate zone group, including where it covers, the 99% winter and 1% summer design temperatures used by Manual J, heating and cooling degree days base 65 F, IECC 2021 R-value targets for new construction, and the HVAC pairing most installers use. This is the data the calculator above shows for your specific ZIP, listed once across all eight zones for cross-reference.
| Zone | Where it covers | Winter design (F) | Summer design (F) | HDD 65 | CDD 65 | R-attic | R-wall | R-floor |
|---|---|---|---|---|---|---|---|---|
| Zone 1 | South Florida (Miami, Key West), most of Hawaii, Guam, Puerto Rico. | 55 to 65 | 90 to 95 | 200 | 4,500 | R-30 | R-13 | R-13 |
| Zone 2 | Houston, New Orleans, Phoenix, Tampa, San Antonio, Las Vegas (south). | 30 to 40 | 95 to 105 | 1,500 | 3,000 | R-49 | R-13 | R-13 |
| Zone 3 | Atlanta, Dallas, Memphis, Charlotte, Oklahoma City, Tucson, Los Angeles (3B/3C). | 20 to 35 | 90 to 100 | 3,000 | 2,000 | R-49 | R-20 | R-19 |
| Zone 4 | New York, Philadelphia, Washington DC, Nashville, St Louis, Seattle (4C). | 10 to 20 | 85 to 95 | 4,500 | 1,200 | R-60 | R-30 | R-19 |
| Zone 5 | Chicago, Boston, Cleveland, Pittsburgh, Denver, Salt Lake City. | 0 to 15 | 85 to 92 | 6,000 | 800 | R-60 | R-30 | R-30 |
| Zone 6 | Minneapolis, Milwaukee, Buffalo, Burlington VT, much of Wyoming and Montana. | -10 to 5 | 82 to 90 | 7,500 | 500 | R-60 | R-30 | R-30 |
| Zone 7 | Northern Minnesota, North Dakota, much of interior Alaska south of the Yukon. | -25 to -10 | 78 to 86 | 9,000 | 300 | R-60 | R-30 | R-38 |
| Zone 8 | Interior Alaska (Fairbanks, North Slope, Aleutians). | -50 to -25 | 72 to 80 | 11,000 | 100 | R-60 | R-30 | R-38 |
Sources: IECC 2021 Table R402.1.3 for R-value targets, PNNL climate zone summaries for HDD/CDD averages, ASHRAE 90.1 Appendix B for 1% / 99% design temperature bands.
HVAC system pairing typical for each zone
- Zone 1. Very hot, humid year-round. Cooling load dominates; almost no heating needed. Central AC or heat pump. Heating element rarely used.
- Zone 2. Hot summers with mild winters. Cooling is the dominant load. High-SEER2 heat pump or central AC + gas furnace if available.
- Zone 3. Mixed climate. Cooling load still leads but heating starts to matter. Heat pump dominant. Dual-fuel systems common in 3A/3B.
- Zone 4. Mixed climate with real winters. Heating and cooling loads roughly balanced. Cold-climate heat pump or heat pump + gas furnace dual fuel.
- Zone 5. Cold winters with warm summers. Heating load dominates. Gas furnace + AC, or cold-climate heat pump with electric strip backup.
- Zone 6. Very cold winters. Heating is the priority; cooling is light. High-AFUE gas furnace + AC, or cold-climate heat pump in dual fuel.
- Zone 7. Extremely cold winters. Major heating loads with minimal cooling needs. Gas or propane furnace dominant. Cold-climate heat pumps work but need backup.
- Zone 8. Subarctic. Heat 365 days a year in extreme cases. Cooling is rare. Oil or propane furnace. Heat pumps only with sized electric backup.
Building America climate zones: the DOE research definition
The Department of Energy's Building America program uses eight named zones instead of numbers: Subarctic, Very Cold, Cold, Marine, Mixed-Humid, Mixed-Dry, Hot-Humid, and Hot-Dry. These are coarser than IECC and group counties by HVAC strategy rather than by code minimum. Hot-Humid means high latent loads and serious humidity control. Hot-Dry means high sensible loads and evaporative cooling potential. Marine means heating dominance with minimal cooling.
Building America zones are what you see referenced in federal rebate programs, ENERGY STAR Most Efficient lists, and DOE technology reports. Cold-climate heat pump certifications require performance testing at the Building America Cold-Zone design temperature, which is why a unit "qualified for cold climates" performs differently in Mixed-Humid Atlanta versus Cold Cleveland.
Building America zone reference
- Hot-Humid. High summer dew points. Latent (humidity) load is large; dehumidification matters as much as cooling. Maps to IECC 1A, 2A, 3A.
- Hot-Dry. High dry-bulb temperatures with low humidity. Sensible cooling dominates; evaporative options can work. Maps to IECC 2B, 3B.
- Mixed-Humid. Hot humid summers and real winters. Both heating and cooling matter; humidity control year-round. Maps to IECC 3A, 4A.
- Mixed-Dry. Hot dry summers and cold winters. Sensible loads dominate both seasons. Maps to IECC 4B.
- Marine. Mild winters and cool summers with high humidity. Heating dominant; little cooling needed. Maps to IECC 3C, 4C, 5C.
- Cold. Long cold winters with warm summers. Heating dominates; insulation and air sealing pay back fast. Maps to IECC 5A, 5B, 6A, 6B.
- Very Cold. Severe winters with brief summers. Heating system reliability matters more than efficiency in some cases. Maps to IECC 7, 7A, 7B.
- Subarctic. Heating-only climate. Cooling is rarely needed; even ventilation is a heating concern. Maps to IECC 7AK, 8, 8AK.
Heating and cooling degree days for your ZIP
HDD and CDD measure how much heating or cooling a building actually needs over a typical year. HDD base 65 F counts every degree-day below 65 F. CDD base 65 F counts every degree-day above 65 F. A Phoenix ZIP runs about 1,500 HDD and 3,000 CDD. A Minneapolis ZIP runs about 7,500 HDD and 500 CDD. Same zone numbering tier, opposite system priority.
Annual operating cost scales linearly with degree days. If you double the HDD, you double the gas usage. This is why the same SEER2 18 heat pump pays back in 4 years in Houston (high CDD) but takes 9 years to pay back in Seattle (low CDD). The degree-day numbers in the result panel are the published NOAA Climate Normals averages for your zone, not for your specific ZIP. Per-ZIP precision is on the roadmap.
Design temperatures: what HVAC contractors actually size for
The 99% winter design temperature is the temperature your area falls below for only 1% of the year, about 88 hours. The 1% summer design temperature is the temperature your area exceeds for only 1% of the year. ACCA Manual J sizes the heating and cooling load to those two anchors, not to record extremes. A Minneapolis 99% winter design is around minus 11 F. A Phoenix 1% summer design is around 108 F. These are the numbers feeding the BTU sizer, the heat loss calculator, and the heat pump sizing tool on this site.
Where ASHRAE 90.1 and IECC differ is in dehumidification design. ASHRAE 90.1 specifies a 1% wet-bulb design temperature for humid zones (1A through 4A) so contractors can size the latent removal capacity. IECC does not. If you live in a humid zone and your HVAC quote only mentions the dry-bulb design temperature, ask for the wet-bulb number too.
How to use this map to size your HVAC system
Three-step workflow. First, look up your ZIP above and note your IECC zone. Second, click a sizing tool from the result panel and your zone pre-fills the dropdown. Third, run the sizing math. The BTU sizer adjusts the per-square-foot load by zone, the heat pump sizing calculator pulls the design temperature from your zone, and the rebate finder filters federal and state incentives that match your zone tier.
If you are talking to an HVAC contractor about a new install, the right questions to ask are: "What IECC zone are you sizing for?" and "What design temperature are you using in Manual J?" A contractor who answers both with confidence is doing real engineering. One who hedges or says "we just go by square footage" is probably going to oversize by 30% and short-cycle your equipment for the next 15 years.
Climate zone by state: full US list
The map above shows the dominant IECC climate zone for every state. Many states span two zones, especially California (3B / 4B / 5B from south to north), Texas (2A / 2B / 3A / 3B), and Florida (1A / 2A). The table below is the state-level summary. For a precise zone at your address, use the ZIP lookup at the top of the page.
| State | IECC zone | Building America |
|---|---|---|
| Alaska | Zone 8 | Subarctic |
| Alabama | Zone 3 | Hot-Humid |
| Arkansas | Zone 3 | Mixed-Humid |
| Arizona | Zone 2 | Hot-Dry |
| California | Zone 3 | Hot-Dry |
| Colorado | Zone 5 | Cold |
| Connecticut | Zone 5 | Cold |
| District of Columbia | Zone 4 | Mixed-Humid |
| Delaware | Zone 4 | Mixed-Humid |
| Florida | Zone 2 | Hot-Humid |
| Georgia | Zone 3 | Mixed-Humid |
| Hawaii | Zone 1 | Hot-Humid |
| Iowa | Zone 5 | Cold |
| Idaho | Zone 5 | Cold |
| Illinois | Zone 5 | Cold |
| Indiana | Zone 5 | Cold |
| Kansas | Zone 4 | Mixed-Humid |
| Kentucky | Zone 4 | Mixed-Humid |
| Louisiana | Zone 2 | Hot-Humid |
| Massachusetts | Zone 5 | Cold |
| Maryland | Zone 4 | Mixed-Humid |
| Maine | Zone 6 | Cold |
| Michigan | Zone 5 | Cold |
| Minnesota | Zone 6 | Cold |
| Missouri | Zone 4 | Mixed-Humid |
| Mississippi | Zone 3 | Hot-Humid |
| Montana | Zone 6 | Cold |
| North Carolina | Zone 3 | Mixed-Humid |
| North Dakota | Zone 7 | Very Cold |
| Nebraska | Zone 5 | Cold |
| New Hampshire | Zone 6 | Cold |
| New Jersey | Zone 4 | Mixed-Humid |
| New Mexico | Zone 5 | Cold |
| Nevada | Zone 5 | Cold |
| New York | Zone 5 | Cold |
| Ohio | Zone 5 | Cold |
| Oklahoma | Zone 3 | Mixed-Humid |
| Oregon | Zone 4 | Marine |
| Pennsylvania | Zone 5 | Cold |
| Rhode Island | Zone 5 | Cold |
| South Carolina | Zone 3 | Hot-Humid |
| South Dakota | Zone 6 | Cold |
| Tennessee | Zone 4 | Mixed-Humid |
| Texas | Zone 2 | Hot-Humid |
| Utah | Zone 5 | Cold |
| Virginia | Zone 4 | Mixed-Humid |
| Vermont | Zone 6 | Cold |
| Washington | Zone 4 | Marine |
| Wisconsin | Zone 6 | Cold |
| West Virginia | Zone 4 | Mixed-Humid |
| Wyoming | Zone 6 | Cold |
Federal rebates by climate zone
The Inflation Reduction Act's HEAR and HOMES programs both segment incentives by climate zone. Cold-climate zones (5-8) get higher rebate caps on heat pump installs because the federal cost-of-conversion math is more favorable up north. Some states layer their own extra incentives on top of federal HEAR. Your zone determines which version of the cold-climate heat pump qualifies for the higher rebate tier. The rebate finder linked from the result panel filters by zone automatically.