Grayson County is in IECC Climate Zone 3A (Warm - Humid). Get accurate Manual J load calculations with official ASHRAE design temperatures for Grayson County.
Grayson County, Texas is classified under IECC Climate Zone 3A (Warm - Humid), a mixed-climate region with humid moisture conditions. With 18 ZIP codes and 1 communities, every HVAC installation in Grayson County must use the ASHRAE design temperatures of 20°F (99% winter heating) and 100°F (1% summer cooling) for accurate Manual J load calculations.
With balanced heating and cooling loads, Grayson 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 Grayson County, TX.
| 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 Grayson County blueprint and get a professional Manual J report in 60 seconds— first report is FREE. Pre-loaded with Grayson County's exact design temperatures (20°F winter / 100°F summer).
Enter your ZIP code to confirm it's in Grayson County and get climate zone details.
Official ASHRAE design temperatures for Grayson County, TX, used for accurate Manual J load calculations.
Minimum insulation and window requirements for Grayson 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 Grayson County share Climate Zone 3A requirements.
Compare climate zones with other counties in Texas. Different zones require different HVAC equipment sizing.
Upload your Grayson County blueprint and get a professional Manual J load calculation using official Zone 3A design temperatures. First report is FREE.
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