Mixed - Dry - Mixed climate with low humidity, warm summers and cold winters. Significant heating and cooling needs. Get IECC 2021 R-values, design temperatures, and free Manual J calculations.
IECC Climate Zone 4B (Mixed - Dry) is a mixed-climate zone requiring careful balance between heating and cooling equipment sizing. Covering parts of 4 states including Arizona, Colorado, New Mexico and 1 more, Zone 4B has a winter 99% design temperature of 3°F and a summer 1% design temperature of 92°F — a 89°F temperature swing that HVAC systems must handle. The dry moisture regime means minimal latent cooling loads but careful attention to winter humidification is needed. 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 4B.
| Building Component | Zone 4B 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 4B.
Official design temperatures for Climate Zone 4B 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 4B 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
Low humidity climate with minimal moisture concerns
Typical equipment specifications for Climate Zone 4B installations.
Climate Zone 4B covers 4 states across the United States. Click a state to see city-specific climate data and Manual J load calculations.
Climate Zone 4B includes parts of Arizona, Colorado, New Mexico, and Utah. This zone represents a balanced climate with dry moisture conditions.
The official ASHRAE design temperatures for Climate Zone 4B are:
For Climate Zone 4B (Mixed - Dry), recommended HVAC equipment includes:
Typical AFUE: 92-96%
Typical SEER: 14-16 SEER
IECC 2021 requires the following minimum R-values for Climate Zone 4B:
Climate Zone 4B is a balanced climate. This means heating and cooling loads are relatively balanced, requiring careful sizing of both heating and cooling equipment.
Zone 4B has a dry moisture regime. This means low humidity levels, minimal dehumidification requirements, and focus on proper winter humidification to prevent dry air issues.
Our AI-powered Manual J calculator uses official Zone 4B design temperatures (3°F winter / 92°F summer) and IECC requirements for pinpoint accuracy. First report is FREE.
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