Marin County is in IECC Climate Zone 3C (Warm - Marine). Get accurate Manual J load calculations with official ASHRAE design temperatures for Marin County.
Marin County, California is classified under IECC Climate Zone 3C (Warm - Marine), a mixed-climate region with marine moisture conditions. With 42 ZIP codes and 1 communities, every HVAC installation in Marin County must use the ASHRAE design temperatures of 27°F (99% winter heating) and 97°F (1% summer cooling) for accurate Manual J load calculations.
With balanced heating and cooling loads, Marin County homes require well-rounded insulation — R-20 walls, R-30 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 3C in Marin County, CA.
| Building Component | Minimum Requirement | Unit |
|---|---|---|
| Ceiling / Attic Insulation | R-30 | 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 3C requires precise load calculations. Upload your Marin County blueprint and get a professional Manual J report in 60 seconds— first report is FREE. Pre-loaded with Marin County's exact design temperatures (27°F winter / 97°F summer).
Enter your ZIP code to confirm it's in Marin County and get climate zone details.
Official ASHRAE design temperatures for Marin County, CA, used for accurate Manual J load calculations.
Minimum insulation and window requirements for Marin County per IECC 2021 energy code.
Climate Zone 3C: Warm - Marine - Mild, marine climate with cool summers and mild winters. Moderate heating needs, minimal cooling.
1 cities and communities in Marin County share Climate Zone 3C requirements.
Compare climate zones with other counties in California. Different zones require different HVAC equipment sizing.
Upload your Marin County blueprint and get a professional Manual J load calculation using official Zone 3C design temperatures. First report is FREE.
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