Humboldt County is in IECC Climate Zone 4C (Mixed - Marine). Get accurate Manual J load calculations with official ASHRAE design temperatures for Humboldt County.
Humboldt County, California is classified under IECC Climate Zone 4C (Mixed - Marine), a mixed-climate region with marine moisture conditions. With 38 ZIP codes and 1 communities, every HVAC installation in Humboldt County must use the ASHRAE design temperatures of 24°F (99% winter heating) and 97°F (1% summer cooling) for accurate Manual J load calculations.
With balanced heating and cooling loads, Humboldt County homes require well-rounded insulation — R-20 walls, R-49 ceilings, R-19 floors — and windows with both U-factor 0.32 and SHGC 0.4 to handle both winter lows and summer highs.
Minimum insulation R-values and window performance for Climate Zone 4C in Humboldt County, CA.
| Building Component | Minimum Requirement | Unit |
|---|---|---|
| Ceiling / Attic Insulation | R-49 | R-value |
| Wall Insulation | R-20 | R-value |
| Floor Insulation | R-19 | R-value |
| Window U-Factor | 0.32 | BTU/hr-ft²-°F |
| Window SHGC | 0.4 | Coefficient |
| Air Infiltration | 0.15 | ACH50 |
Climate Zone 4C requires precise load calculations. Upload your Humboldt County blueprint and get a professional Manual J report in 60 seconds— first report is FREE. Pre-loaded with Humboldt County's exact design temperatures (24°F winter / 97°F summer).
Enter your ZIP code to confirm it's in Humboldt County and get climate zone details.
Official ASHRAE design temperatures for Humboldt County, CA, used for accurate Manual J load calculations.
Minimum insulation and window requirements for Humboldt County per IECC 2021 energy code.
Climate Zone 4C: Mixed - Marine - Marine climate with mild, wet winters and cool summers. Moderate heating needs, minimal cooling.
1 cities and communities in Humboldt County share Climate Zone 4C requirements.
Compare climate zones with other counties in California. Different zones require different HVAC equipment sizing.
Upload your Humboldt County blueprint and get a professional Manual J load calculation using official Zone 4C design temperatures. First report is FREE.
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