Colorado spans 3 IECC climate zones. Find your exact zone, design temperatures, and get free Manual J load calculations for any Colorado location.
Colorado spans 3 IECC climate zones (Zone 4B, Zone 5B, Zone 6B), which means insulation requirements, design temperatures, and equipment specs vary significantly depending on location. The primary zone, Zone 4B (Mixed - Dry), is a mixed climate, with winter design temperatures as low as 3°F and summer highs reaching 92°F. HVAC contractors working across Colorado need to verify the exact climate zone for each job site — using the wrong zone data leads to oversized or undersized equipment, failed inspections, and unhappy homeowners.
Minimum insulation R-values and window specifications required by the 2021 International Energy Conservation Code for Colorado.
| Component | Zone 4B | Zone 5B | Zone 6B |
|---|---|---|---|
| Ceiling / Attic | R-49 | R-49 | R-49 |
| Walls | R-20 | R-20 | R-20 |
| Floor | R-19 | R-30 | R-30 |
| Window U-Factor | 0.32 | 0.3 | 0.3 |
| Window SHGC | 0.4 | 0.4 | 0.4 |
Source: IECC 2021 Table R402.1.2. Requirements shown are for residential construction. Colorado contractors must use the zone that corresponds to the job site location.
These ASHRAE design temperatures determine how Manual J load calculations size heating and cooling equipment for Colorado homes. The winter 99% value represents the coldest temperature expected, while the summer 1% value represents the hottest.
Mixed - Dry
Cool - Dry
Cold - Dry
Based on Climate Zone 4B (Mixed - Dry), here are typical HVAC equipment specifications for Colorado installations.
Annual Fuel Utilization Efficiency for Colorado furnaces
Seasonal Energy Efficiency Ratio for Colorado AC systems
Colorado's climate zone data ensures proper equipment sizing. No more callbacks from oversized or undersized systems.
Colorado building departments require IECC-compliant Manual J calculations. Our tool uses official Colorado climate data.
Right-sized systems based on Colorado climate data reduce energy costs for homeowners and improve your reputation.
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