Vermont is in IECC Climate Zone 6A (Cold - Humid). Get accurate Manual J load calculations with official design temperatures and IECC requirements.
Vermont falls entirely within IECC Climate Zone 6A (Cold - Humid), making it a heating-dominated state where furnace capacity and insulation R-values are the primary sizing concerns. With a winter 99% design temperature of -9°F and a summer 1% design temperature of 89°F, Vermont HVAC contractors must size systems for a 98°F temperature swing between extreme winter and summer conditions. Proper Manual J load calculations using these design temperatures are essential for code-compliant, right-sized installations that avoid callbacks and comfort complaints.
Minimum insulation R-values and window specifications required by the 2021 International Energy Conservation Code for Vermont.
| Component | Zone 6A |
|---|---|
| Ceiling / Attic | R-49 |
| Walls | R-20 |
| Floor | R-30 |
| Window U-Factor | 0.3 |
| Window SHGC | 0.4 |
Source: IECC 2021 Table R402.1.2. Requirements shown are for residential construction.
These ASHRAE design temperatures determine how Manual J load calculations size heating and cooling equipment for Vermont homes. The winter 99% value represents the coldest temperature expected, while the summer 1% value represents the hottest.
Cold - Humid
Based on Climate Zone 6A (Cold - Humid), here are typical HVAC equipment specifications for Vermont installations.
Annual Fuel Utilization Efficiency for Vermont furnaces
Seasonal Energy Efficiency Ratio for Vermont AC systems
Vermont's climate zone data ensures proper equipment sizing. No more callbacks from oversized or undersized systems.
Vermont building departments require IECC-compliant Manual J calculations. Our tool uses official Vermont climate data.
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