Climate ZonesWashingtonSeattle

Seattle, Washington HVAC Climate Zone

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

Climate Zone
4C
Winter Design
29°F
Summer Design
85°F
ZIP Codes
62

Seattle HVAC Contractors: Get Your Free Manual J Report

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

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Verify Your Seattle ZIP Code

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

Seattle covers 62 ZIP codes: 98101, 98102, 98103, 98104, 98105, 98106, 98107, 98108, 98109, 98110 and 52 more

Seattle Design Temperatures

Official ASHRAE design temperatures for Seattle, 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 Seattle 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 Seattle

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
Seattle, Washington

Get Free Manual J Calculations for Seattle

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

Seattle design temps
Zone 4C compliant
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