Houston is in IECC Climate Zone 2A (Hot - Humid). Get accurate Manual J load calculations with official design temperatures for Houston.
Houston, Texas falls within IECC Climate Zone 2A (Hot - Humid), a cooling-dominated region with humid moisture conditions. HVAC contractors working in Houston must use the official ASHRAE design temperatures of 32°F (99% winter) and 95°F (1% summer) when performing Manual J load calculations. These values represent the outdoor conditions your heating and cooling system must handle 99% and 1% of the year, respectively — ensuring proper equipment sizing without costly over- or under-sizing.
Because Zone 2A is cooling-dominated, solar heat gain control is critical. Houston homes require windows with an SHGC of 0.25 or lower, along with R-13 wall insulation and R-30 ceiling insulation per the IECC 2021 energy code.
Minimum insulation R-values and window performance requirements for Climate Zone 2A in Houston, Texas.
| Building Component | Minimum Requirement | Unit |
|---|---|---|
| Ceiling / Attic Insulation | R-30 | R-value |
| Wall Insulation | R-13 | R-value |
| Floor Insulation | R-13 | R-value |
| Window U-Factor | 0.4 | BTU/hr-ft²-°F |
| Window SHGC | 0.25 | Coefficient |
| Air Infiltration | 0.25 | ACH50 |
Climate Zone 2A requires precise load calculations. Upload your Houston blueprint and get a professional Manual J report in 60 seconds— first report is FREE. Pre-loaded with Houston's exact design temperatures (32°F winter / 95°F summer).
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Official ASHRAE design temperatures for Houston, used for accurate Manual J load calculations.
Minimum insulation and window requirements for Houston per IECC 2021.
Energy Code: 2021 IECC
Upload your Houston blueprint and get a professional Manual J load calculation using official Zone 2A design temperatures. First report is FREE.
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