Lewis County is in IECC Climate Zone 4C (Mixed - Marine). Get accurate Manual J load calculations with official ASHRAE design temperatures for Lewis County.
Lewis County, Washington is classified under IECC Climate Zone 4C (Mixed - Marine), a mixed-climate region with marine moisture conditions. With 23 ZIP codes and 1 communities, every HVAC installation in Lewis 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, Lewis 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 Lewis 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 Lewis County blueprint and get a professional Manual J report in 60 seconds— first report is FREE. Pre-loaded with Lewis County's exact design temperatures (24°F winter / 84°F summer).
Enter your ZIP code to confirm it's in Lewis County and get climate zone details.
Official ASHRAE design temperatures for Lewis County, WA, used for accurate Manual J load calculations.
Minimum insulation and window requirements for Lewis 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 Lewis County share Climate Zone 4C requirements.
Compare climate zones with other counties in Washington. Different zones require different HVAC equipment sizing.
Upload your Lewis County blueprint and get a professional Manual J load calculation using official Zone 4C design temperatures. First report is FREE.
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