Mason County is in IECC Climate Zone 4C (Mixed - Marine). Get accurate Manual J load calculations with official ASHRAE design temperatures for Mason County.
Mason County, Washington is classified under IECC Climate Zone 4C (Mixed - Marine), a mixed-climate region with marine moisture conditions. With 9 ZIP codes and 1 communities, every HVAC installation in Mason County must use the ASHRAE design temperatures of 24°F (99% winter heating) and 84°F (1% summer cooling) for accurate Manual J load calculations.
With balanced heating and cooling loads, Mason 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 Mason County, WA.
| 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 Mason County blueprint and get a professional Manual J report in 60 seconds— first report is FREE. Pre-loaded with Mason County's exact design temperatures (24°F winter / 84°F summer).
Enter your ZIP code to confirm it's in Mason County and get climate zone details.
Official ASHRAE design temperatures for Mason County, WA, used for accurate Manual J load calculations.
Minimum insulation and window requirements for Mason 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 Mason County share Climate Zone 4C requirements.
Compare climate zones with other counties in Washington. Different zones require different HVAC equipment sizing.
Upload your Mason County blueprint and get a professional Manual J load calculation using official Zone 4C design temperatures. First report is FREE.
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