Lewis County is in IECC Climate Zone 5B (Cool - Dry). Get accurate Manual J load calculations with official ASHRAE design temperatures for Lewis County.
Lewis County, Idaho is classified under IECC Climate Zone 5B (Cool - Dry), a heating-dominated region with dry moisture conditions. With 3 ZIP codes and 1 communities, every HVAC installation in Lewis County must use the ASHRAE design temperatures of 15°F (99% winter heating) and 95°F (1% summer cooling) for accurate Manual J load calculations.
As a heating-dominated zone, Lewis County requires robust insulation — a minimum of R-20 in walls, R-49 in ceilings, and R-30 in floors. Windows must meet a U-factor of 0.3 or lower. These requirements ensure homes maintain comfort during the coldest 15°F design conditions.
Minimum insulation R-values and window performance for Climate Zone 5B in Lewis County, ID.
| Building Component | Minimum Requirement | Unit |
|---|---|---|
| Ceiling / Attic Insulation | R-49 | R-value |
| Wall Insulation | R-20 | R-value |
| Floor Insulation | R-30 | R-value |
| Window U-Factor | 0.3 | BTU/hr-ft²-°F |
| Window SHGC | 0.4 | Coefficient |
| Air Infiltration | 0.15 | ACH50 |
Climate Zone 5B 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 (15°F winter / 95°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, ID, used for accurate Manual J load calculations.
Minimum insulation and window requirements for Lewis County per IECC 2021 energy code.
Climate Zone 5B: Cool - Dry - Heating-dominated with cold, dry winters and warm summers. High heating loads in winter, moderate cooling needs.
1 cities and communities in Lewis County share Climate Zone 5B requirements.
Compare climate zones with other counties in Idaho. Different zones require different HVAC equipment sizing.
Upload your Lewis County blueprint and get a professional Manual J load calculation using official Zone 5B design temperatures. First report is FREE.
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