Climate ZonesWashingtonWhatcom

Whatcom, Washington HVAC Climate Zone

Whatcom is located in IECC Climate Zone 4C (Mixed - Marine). Get accurate Manual J load calculations with official design temperatures for Whatcom.

Climate Zone
4C
Winter Design
29°F
Summer Design
85°F
ZIP Codes
12

Whatcom HVAC Contractors: Get Your Free Manual J Report

Climate Zone 4C requires precise load calculations. Upload your Whatcom blueprint and get a professional Manual J report in 60 seconds— first report is FREE. Pre-loaded with Whatcom's exact design temperatures (29°F winter / 85°F summer).

Claim Free Report
No credit card required

Verify Your Whatcom ZIP Code

Enter your ZIP code to confirm it's in Whatcom and get climate zone details.

Whatcom covers 12 ZIP codes: 98220, 98225, 98226, 98230, 98240, 98244, 98247, 98248, 98262, 98264 and 2 more

Whatcom Design Temperatures

Official ASHRAE design temperatures for Whatcom, used for accurate Manual J load calculations.

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

IECC Requirements for Zone 4C

Minimum insulation and window requirements for Whatcom per IECC 2021.

Wall Insulation:R-20
Roof/Ceiling:R-49
Floor Insulation:R-19
Window U-Factor:0.32
Window SHGC:0.4

Energy Code: 2021 IECC

Recommended HVAC Equipment for Whatcom

Heating Systems

Gas furnace
Heat pump
Typical AFUE
92-95%

Cooling Systems

AC (optional)
Heat pump
Typical SEER
14 SEER

Related Climate Zone Pages

Learn More About
Climate Zone 4C
View All Zones in
Washington
HVAC Permits for
Whatcom, Washington

Get Free Manual J Calculations for Whatcom

Upload your Whatcom blueprint and get a professional Manual J load calculation using official Zone 4C design temperatures. First report is FREE.

Whatcom design temps
Zone 4C compliant
Ready in 60 seconds
Upload Blueprint → Get Free Report

Join 10,000+ Whatcom contractors who trust AutoHVAC