Zone 4CMixed (Zone 4)
Climate Zone 4C - Mixed, Marine
Mild temperatures with marine influence. Moderate heating needs, minimal cooling. This climate zone encompasses parts of Washington, Oregon and includes major cities like Seattle, Portland, Olympia, Salem.
Design Temperatures
Winter Design Temperatures
20°F to 35°F
Used for heating load calculations and equipment sizing
Summer Design Temperatures
70°F to 80°F
Used for cooling load calculations and equipment sizing
Heating & Cooling Degree Days
Heating Degree Days (HDD)
3,000 - 5,000
Base 65°F. Higher numbers indicate more heating requirements and longer heating seasons.
Cooling Degree Days (CDD)
0 - 500
Base 65°F. Higher numbers indicate more cooling requirements and longer cooling seasons.
HVAC System Considerations
Key Considerations
- •Heating priority
- •Minimal cooling needs
- •High humidity management
- •Corrosion resistance
- •Mold prevention
Common Equipment
- ✓Heat pumps
- ✓Gas furnaces
- ✓Ductless mini-splits
- ✓Radiant heating systems
Energy Code Requirements
Equipment Efficiency
- ⚠SEER 13+ minimum
- ⚠HSPF 8.2+ for heat pumps
- ⚠AFUE 80+ for furnaces
- ⚠Ventilation requirements
Insulation Requirements
Walls:R-15 to R-20
Ceiling:R-38 to R-49
Floor:R-25 to R-30
States with Zone 4C Areas
Quick Reference
Zone:4C
Temperature:Mixed
Moisture:Marine (C)
States:2
Cities:4
Calculate Load
Use our load calculators with the design temperatures and requirements specific to Zone 4C.