Johnston County is in IECC Climate Zone 3A (Warm - Humid). Get accurate Manual J load calculations with official ASHRAE design temperatures for Johnston County.
Johnston County, Oklahoma is classified under IECC Climate Zone 3A (Warm - Humid), a mixed-climate region with humid moisture conditions. With 9 ZIP codes and 1 communities, every HVAC installation in Johnston County must use the ASHRAE design temperatures of 14°F (99% winter heating) and 100°F (1% summer cooling) for accurate Manual J load calculations.
With balanced heating and cooling loads, Johnston County homes require well-rounded insulation — R-20 walls, R-30 ceilings, R-19 floors — and windows with both U-factor 0.32 and SHGC 0.25 to handle both winter lows and summer highs.
Minimum insulation R-values and window performance for Climate Zone 3A in Johnston County, OK.
| 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 | 0.25 | Coefficient |
| Air Infiltration | 0.15 | ACH50 |
Climate Zone 3A requires precise load calculations. Upload your Johnston County blueprint and get a professional Manual J report in 60 seconds— first report is FREE. Pre-loaded with Johnston County's exact design temperatures (14°F winter / 100°F summer).
Enter your ZIP code to confirm it's in Johnston County and get climate zone details.
Official ASHRAE design temperatures for Johnston County, OK, used for accurate Manual J load calculations.
Minimum insulation and window requirements for Johnston County per IECC 2021 energy code.
Climate Zone 3A: Warm - Humid - Mixed climate with warm, humid summers and cool winters. Balanced heating and cooling needs.
1 cities and communities in Johnston County share Climate Zone 3A requirements.
Compare climate zones with other counties in Oklahoma. Different zones require different HVAC equipment sizing.
Upload your Johnston County blueprint and get a professional Manual J load calculation using official Zone 3A design temperatures. First report is FREE.
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