Napa is in IECC Climate Zone 3C (Warm - Marine). Get accurate Manual J load calculations with official design temperatures for Napa.
Napa, California falls within IECC Climate Zone 3C (Warm - Marine), a mixed-climate region with marine moisture conditions. HVAC contractors working in Napa must use the official ASHRAE design temperatures of 41°F (99% winter) and 81°F (1% summer) when performing Manual J load calculations. These values represent the outdoor conditions your heating and cooling system must handle 99% and 1% of the year, respectively — ensuring proper equipment sizing without costly over- or under-sizing.
Zone 3C experiences both significant heating and cooling loads. Napa homes need balanced insulation — R-20 walls, R-30 ceilings — plus windows with U-factor 0.32 and SHGC 0.4 per the IECC 2021 energy code.
Minimum insulation R-values and window performance requirements for Climate Zone 3C in Napa, California.
| 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 Napa blueprint and get a professional Manual J report in 60 seconds— first report is FREE. Pre-loaded with Napa's exact design temperatures (41°F winter / 81°F summer).
Enter your ZIP code to confirm it's in Napa and get climate zone details.
Official ASHRAE design temperatures for Napa, used for accurate Manual J load calculations.
Minimum insulation and window requirements for Napa per IECC 2021.
Energy Code: 2022 Title 24
Upload your Napa blueprint and get a professional Manual J load calculation using official Zone 3C design temperatures. First report is FREE.
Join 10,000+ Napa contractors who trust AutoHVAC