St. Clair County is in IECC Climate Zone 5A (Cool - Humid). Get accurate Manual J load calculations with official ASHRAE design temperatures for St. Clair County.
St. Clair County, Michigan is classified under IECC Climate Zone 5A (Cool - Humid), a heating-dominated region with humid moisture conditions. With 23 ZIP codes and 1 communities, every HVAC installation in St. Clair County must use the ASHRAE design temperatures of 4°F (99% winter heating) and 90°F (1% summer cooling) for accurate Manual J load calculations.
As a heating-dominated zone, St. Clair 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 4°F design conditions.
Minimum insulation R-values and window performance for Climate Zone 5A in St. Clair County, MI.
| 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 5A requires precise load calculations. Upload your St. Clair County blueprint and get a professional Manual J report in 60 seconds— first report is FREE. Pre-loaded with St. Clair County's exact design temperatures (4°F winter / 90°F summer).
Enter your ZIP code to confirm it's in St. Clair County and get climate zone details.
Official ASHRAE design temperatures for St. Clair County, MI, used for accurate Manual J load calculations.
Minimum insulation and window requirements for St. Clair County per IECC 2021 energy code.
Climate Zone 5A: Cool - Humid - Heating-dominated climate with cold winters and warm, humid summers. High heating loads, moderate cooling needs.
1 cities and communities in St. Clair County share Climate Zone 5A requirements.
Compare climate zones with other counties in Michigan. Different zones require different HVAC equipment sizing.
Upload your St. Clair County blueprint and get a professional Manual J load calculation using official Zone 5A design temperatures. First report is FREE.
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