Climate ZonesZone 4C

Climate Zone 4C: Mixed - Marine

Marine climate with mild, wet winters and cool summers. Moderate heating needs, minimal cooling.

Load Characteristic
Balanced Loads
Moisture Regime
Marine
States Covered
3 States

ASHRAE Design Temperatures

Official design temperatures for Climate Zone 4C per ASHRAE Fundamentals 2021. These values are critical for accurate Manual J load calculations.

Winter Design Temp
29°F

99% design temperature for heating load calculations (coldest expected temperature)

Summer Design Temp
85°F

1% design temperature for cooling load calculations (hottest expected temperature)

Wet Bulb Temp
67°F

Summer wet-bulb for latent cooling load and dehumidification calculations

2021 IECC Insulation Requirements

Minimum insulation and window specifications for Climate Zone 4C per the International Energy Conservation Code (IECC) 2021.

Wall Insulation
R-20

Minimum wall R-value (continuous insulation or cavity + continuous)

Roof/Ceiling Insulation
R-49

Minimum attic/ceiling R-value for energy compliance

Floor Insulation
R-19

Minimum floor R-value (over unconditioned space)

Window U-Factor
0.32

Maximum window U-factor (lower is better insulation)

Window SHGC
0.40

Recommended Solar Heat Gain Coefficient

Air Infiltration
0.15

Typical ACH (air changes per hour) for load calculations

Moisture Regime: Marine

Moderate temperatures with high moisture from ocean influence

Key Considerations for Marine Climates:

  • Year-round moisture management
  • Corrosion-resistant equipment
  • Marine-grade installations

Recommended HVAC Equipment

Typical equipment specifications for Climate Zone 4C installations.

Heating Systems

Gas furnace
Heat pump
Typical AFUE
92-95%

Cooling Systems

AC (optional)
Heat pump
Typical SEER
14 SEER

States in Climate Zone 4C

Climate Zone 4C covers 3 states across the United States. Click a state to see city-specific climate data and Manual J load calculations.

California
Oregon
Washington

Frequently Asked Questions About Climate Zone 4C

Q1What states are in Climate Zone 4C?

Climate Zone 4C includes parts of California, Oregon, and Washington. This zone represents a balanced climate with marine moisture conditions.

Q2What are the design temperatures for Zone 4C?

The official ASHRAE design temperatures for Climate Zone 4C are:

  • Winter 99% Design Temp: 29°F
  • Summer 1% Design Temp: 85°F
  • Summer Wet Bulb: 67°F

Q3What equipment works best in Climate Zone 4C?

For Climate Zone 4C (Mixed - Marine), recommended HVAC equipment includes:

Heating Systems:
  • • Gas furnace
  • • Heat pump

Typical AFUE: 92-95%

Cooling Systems:
  • • AC (optional)
  • • Heat pump

Typical SEER: 14 SEER

Q4What R-value insulation is required in Zone 4C?

IECC 2021 requires the following minimum R-values for Climate Zone 4C:

Walls
R-20
Roof
R-49
Floor
R-19
Window U
0.32

Q5Is Zone 4C heating-dominated or cooling-dominated?

Climate Zone 4C is a balanced climate. This means heating and cooling loads are relatively balanced, requiring careful sizing of both heating and cooling equipment.

Q6What is the moisture regime for Zone 4C?

Zone 4C has a marine moisture regime. This means coastal climate with marine influences, moderate humidity, and potential for condensation issues that require proper vapor barriers.

Get Accurate Load Calculations for Zone 4C

Our AI-powered Manual J calculator uses official Zone 4C design temperatures and IECC requirements for pinpoint accuracy. First report is FREE.

Upload Blueprint → Get Free Manual J