Dorchester County is in IECC Climate Zone 4A (Mixed - Humid). Get accurate Manual J load calculations with official ASHRAE design temperatures for Dorchester County.
Dorchester County, Maryland is classified under IECC Climate Zone 4A (Mixed - Humid), a mixed-climate region with humid moisture conditions. With 16 ZIP codes and 1 communities, every HVAC installation in Dorchester County must use the ASHRAE design temperatures of 18°F (99% winter heating) and 91°F (1% summer cooling) for accurate Manual J load calculations.
With balanced heating and cooling loads, Dorchester County homes require well-rounded insulation — R-20 walls, R-49 ceilings, R-19 floors — and windows with both U-factor 0.32 and SHGC 0.4 to handle both winter lows and summer highs.
Minimum insulation R-values and window performance for Climate Zone 4A in Dorchester County, MD.
| Building Component | Minimum Requirement | Unit |
|---|---|---|
| Ceiling / Attic Insulation | R-49 | 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 | 0.4 | Coefficient |
| Air Infiltration | 0.15 | ACH50 |
Climate Zone 4A requires precise load calculations. Upload your Dorchester County blueprint and get a professional Manual J report in 60 seconds— first report is FREE. Pre-loaded with Dorchester County's exact design temperatures (18°F winter / 91°F summer).
Enter your ZIP code to confirm it's in Dorchester County and get climate zone details.
Official ASHRAE design temperatures for Dorchester County, MD, used for accurate Manual J load calculations.
Minimum insulation and window requirements for Dorchester County per IECC 2021 energy code.
Climate Zone 4A: Mixed - Humid - True mixed climate with hot, humid summers and cold winters. Equal emphasis on heating and cooling.
1 cities and communities in Dorchester County share Climate Zone 4A requirements.
Compare climate zones with other counties in Maryland. Different zones require different HVAC equipment sizing.
Upload your Dorchester County blueprint and get a professional Manual J load calculation using official Zone 4A design temperatures. First report is FREE.
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