Mixed - Humid - True mixed climate with hot, humid summers and cold winters. Equal emphasis on heating and cooling. Get IECC 2021 R-values, design temperatures, and free Manual J calculations.
IECC Climate Zone 4A (Mixed - Humid) is a mixed-climate zone requiring careful balance between heating and cooling equipment sizing. Covering parts of 11 states including Delaware, Kansas, Kentucky and 8 more, Zone 4A has a winter 99% design temperature of 13°F and a summer 1% design temperature of 91°F — a 78°F temperature swing that HVAC systems must handle. The humid moisture regime means latent cooling loads are significant, and proper dehumidification capacity is critical for comfort. The IECC 2021 requires minimum wall insulation of R-20, ceiling insulation of R-49, and windows with U-factor 0.32 or lower.
Quick reference table for IECC 2021 minimum insulation and window specifications in Climate Zone 4A.
| Building Component | Zone 4A Requirement |
|---|---|
| Ceiling / Attic | R-49 |
| Exterior Walls | R-20 |
| Floor (over unconditioned space) | R-19 |
| Window U-Factor (max) | 0.32 |
| Window SHGC (max) | 0.40 |
| Typical Air Infiltration (ACH) | 0.15 |
Source: IECC 2021 Table R402.1.2. Values shown are minimums for residential construction in Zone 4A.
Official design temperatures for Climate Zone 4A per ASHRAE Fundamentals 2021. These values are critical for accurate Manual J load calculations.
99% design temperature for heating load calculations (coldest expected temperature)
1% design temperature for cooling load calculations (hottest expected temperature)
Summer wet-bulb for latent cooling load and dehumidification calculations
Minimum insulation and window specifications for Climate Zone 4A per the International Energy Conservation Code (IECC) 2021.
Minimum wall R-value (continuous insulation or cavity + continuous)
Minimum attic/ceiling R-value for energy compliance
Minimum floor R-value (over unconditioned space)
Maximum window U-factor (lower is better insulation)
Recommended Solar Heat Gain Coefficient
Typical ACH (air changes per hour) for load calculations
High humidity climate requiring significant moisture control
Typical equipment specifications for Climate Zone 4A installations.
Climate Zone 4A covers 11 states across the United States. Click a state to see city-specific climate data and Manual J load calculations.
Climate Zone 4A includes parts of Delaware, Kansas, Kentucky, Maryland, Missouri, New Jersey, North Carolina, Oklahoma, Tennessee, Virginia, and West Virginia. This zone represents a balanced climate with humid moisture conditions.
The official ASHRAE design temperatures for Climate Zone 4A are:
For Climate Zone 4A (Mixed - Humid), recommended HVAC equipment includes:
Typical AFUE: 92-96%
Typical SEER: 14-16 SEER
IECC 2021 requires the following minimum R-values for Climate Zone 4A:
Climate Zone 4A is a balanced climate. This means heating and cooling loads are relatively balanced, requiring careful sizing of both heating and cooling equipment.
Zone 4A has a humid moisture regime. This means high humidity levels, significant dehumidification requirements in summer, and careful attention to latent cooling loads in Manual J calculations.
Our AI-powered Manual J calculator uses official Zone 4A design temperatures (13°F winter / 91°F summer) and IECC requirements for pinpoint accuracy. First report is FREE.
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