IECC Climate Zone 3 — Warm HVAC Guide
IECC Climate Zone 3 (Warm) covers regions with summer design temperatures of 88–100°F and winter design temperatures of 16–32°F. Moisture regime subzones: A (Moist) + B (Dry) + C (Marine). Cooling is the dominant HVAC load.
Zone Overview
| Parameter | Value |
|---|---|
| IECC Climate Zone | 3 |
| Climate Type | Warm |
| Moisture Regime Subzones | A (Moist) + B (Dry) + C (Marine) |
| Summer Design Temperature (1%) | 88–100°F |
| Winter Design Temperature (99%) | 16–32°F |
| Heating Degree Days (HDD) | 2,000 – 4,500 |
| Cooling Degree Days (CDD) | 2,000 – 3,500 |
| Dominant Load | Cooling Dominant |
Typical Cities in This Zone
- Atlanta, GA
- Dallas, TX
- San Francisco, CA
- Charlotte, NC
HVAC Design Priorities
- Dual-fuel system (heat pump + gas furnace) is an excellent option
- Cooling and heating loads are both significant — balanced design
- Variable-speed systems provide efficiency across seasonal swings
- ERV/HRV recommended for tight building envelopes in newer construction
- Freeze protection for outdoor equipment in northern parts of the zone
IECC Building Envelope Requirements
| Parameter | Value |
|---|---|
| Wall R-Value (min) | R-20 |
| Ceiling R-Value (min) | R-38 |
| Floor R-Value (min) | R-19 |
| Fenestration U-Factor (max) | 0.35 |
| SEER Minimum | 14 |
Climate Zone Comparison
| Zone | Summer Design Temperature (1%) | Winter Design Temperature (99%) | Wall/Ceiling R | Dominant Load | Typical Cities |
|---|---|---|---|---|---|
| Zone 1 — Very Hot | 88–95°F | 40–55°F | R-13/R-30 | Cooling | Miami, FL, Honolulu, HI |
| Zone 2 — Hot | 90–110°F | 24–38°F | R-13/R-38 | Cooling | Houston, TX, Phoenix, AZ |
| Zone 3 — Warm | 88–100°F | 16–32°F | R-20/R-38 | Cooling | Atlanta, GA, Dallas, TX |
| Zone 4 — Mixed | 84–95°F | 6–22°F | R-20/R-49 | Heating | New York, NY, Washington, DC |
| Zone 5 — Cool | 80–92°F | -4–14°F | R-20/R-49 | Heating | Chicago, IL, Boston, MA |
| Zone 6 — Cold | 78–90°F | -12–2°F | R-20/R-49 | Heating | Minneapolis, MN, Burlington, VT |
| Zone 7 — Very Cold | 74–86°F | -30–-8°F | R-20/R-49 | Heating | Fairbanks, AK, Duluth, MN |
| Zone 8 — Subarctic | 68–80°F | -50–-20°F | R-20/R-60 | Heating | Utqiaġvik (Barrow), AK, Deadhorse, AK |
Frequently Asked Questions
What climate zone is my city in?
Climate Zone 3 covers cities like Atlanta, GA, Dallas, TX, San Francisco, CA. To find your exact climate zone, check the IECC climate zone map or use your ZIP code with the DOE Building Energy Codes Program lookup tool.
What insulation R-value do I need in Climate Zone 3?
IECC 2021 requires minimum R-20 walls, R-38 ceilings, and R-19 floors in Climate Zone 3. Fenestration (windows) must have a maximum U-factor of 0.35.
What HVAC system works best in Climate Zone 3?
In Warm climate (Zone 3), cooling is the primary concern — a high-efficiency AC or heat pump is recommended. Always size equipment using Manual J calculations for your specific home.