Climate Zone 3C - Warm, Marine
Mild temperatures year-round with marine influence. Limited heating and cooling needs. This climate zone encompasses parts of California, Oregon and includes major cities like San Francisco, Los Angeles, San Diego, Eureka.
Common Questions About Zone 3C
Zone 3C definition
This page explains what IECC climate zone 3C means in HVAC and building-code terms.
Cities in zone 3C
Use the city examples below to answer common lookup searches for this zone.
Heating and cooling profile
See whether zone 3C is heating-dominant, cooling-dominant, or balanced.
HVAC requirements
Compare design temperatures, degree days, code requirements, and equipment guidance for this zone.
What IECC Climate Zone 3C Means
Temperature class
Warm (Zone 3)
Moisture class
Marine (C)
Load priority
Heating-dominant
Quick definition
Mild temperatures year-round with marine influence. Limited heating and cooling needs.
Common City Lookups for Zone 3C
| City | IECC zone answer | Why it matters |
|---|---|---|
| San Francisco | San Francisco is commonly treated as IECC climate zone 3C in this guide. | Minimal cooling needs |
| Los Angeles | Los Angeles is commonly treated as IECC climate zone 3C in this guide. | Minimal cooling needs |
| San Diego | San Diego is commonly treated as IECC climate zone 3C in this guide. | Minimal cooling needs |
| Eureka | Eureka is commonly treated as IECC climate zone 3C in this guide. | Minimal cooling needs |
Design Temperatures
Winter Design Temperatures
Used for heating load calculations and equipment sizing
Summer Design Temperatures
Used for cooling load calculations and equipment sizing
Heating & Cooling Degree Days
Heating Degree Days (HDD)
Base 65°F. Higher numbers indicate more heating requirements and longer heating seasons.
Cooling Degree Days (CDD)
Base 65°F. Higher numbers indicate more cooling requirements and longer cooling seasons.
HVAC System Considerations
Key Considerations
- •Minimal cooling needs
- •Moderate heating requirements
- •High humidity from marine air
- •Corrosion from salt air
- •Mild temperature swings
Common Equipment
- ✓Heat pumps
- ✓Ductless mini-splits
- ✓Radiant heating
- ✓High-efficiency gas furnaces
Energy Code Requirements
Equipment Efficiency
- ⚠SEER 13+ minimum
- ⚠HSPF 7.7+ for heat pumps
- ⚠AFUE 80+ for furnaces
- ⚠Enhanced building envelope
Insulation Requirements
Major Cities in Zone 3C
States with Zone 3C Areas
Quick Reference
Calculate Load
Use our load calculators with the design temperatures and requirements specific to Zone 3C.