Custer County is in IECC Climate Zone 6B (Cold - Dry). Get accurate Manual J load calculations with official ASHRAE design temperatures for Custer County.
Custer County, Montana is classified under IECC Climate Zone 6B (Cold - Dry), a heating-dominated region with dry moisture conditions. With 3 ZIP codes and 1 communities, every HVAC installation in Custer County must use the ASHRAE design temperatures of -12°F (99% winter heating) and 95°F (1% summer cooling) for accurate Manual J load calculations.
As a heating-dominated zone, Custer County requires robust insulation — a minimum of R-20 in walls, R-49 in ceilings, and R-30 in floors. Windows must meet a U-factor of 0.3 or lower. These requirements ensure homes maintain comfort during the coldest -12°F design conditions.
Minimum insulation R-values and window performance for Climate Zone 6B in Custer County, MT.
| Building Component | Minimum Requirement | Unit |
|---|---|---|
| Ceiling / Attic Insulation | R-49 | R-value |
| Wall Insulation | R-20 | R-value |
| Floor Insulation | R-30 | R-value |
| Window U-Factor | 0.3 | BTU/hr-ft²-°F |
| Window SHGC | 0.4 | Coefficient |
| Air Infiltration | 0.15 | ACH50 |
Climate Zone 6B requires precise load calculations. Upload your Custer County blueprint and get a professional Manual J report in 60 seconds— first report is FREE. Pre-loaded with Custer County's exact design temperatures (-12°F winter / 95°F summer).
Enter your ZIP code to confirm it's in Custer County and get climate zone details.
Official ASHRAE design temperatures for Custer County, MT, used for accurate Manual J load calculations.
Minimum insulation and window requirements for Custer County per IECC 2021 energy code.
Climate Zone 6B: Cold - Dry - Cold, dry climate with very cold winters and mild summers. Extreme heating requirements, minimal cooling.
1 cities and communities in Custer County share Climate Zone 6B requirements.
Compare climate zones with other counties in Montana. Different zones require different HVAC equipment sizing.
Upload your Custer County blueprint and get a professional Manual J load calculation using official Zone 6B design temperatures. First report is FREE.
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