Boulder is in IECC Climate Zone 5B (Cool - Dry). Get accurate Manual J load calculations with official design temperatures for Boulder.
Boulder, Colorado falls within IECC Climate Zone 5B (Cool - Dry), a heating-dominated region with dry moisture conditions. HVAC contractors working in Boulder must use the official ASHRAE design temperatures of -7°F (99% winter) and 91°F (1% summer) when performing Manual J load calculations. These values represent the outdoor conditions your heating and cooling system must handle 99% and 1% of the year, respectively — ensuring proper equipment sizing without costly over- or under-sizing.
Because Zone 5B is heating-dominated, insulation levels are critical. Boulder homes require a minimum of R-20 wall insulation, R-49 ceiling insulation, and windows with a U-factor of 0.3 or lower per the IECC 2021 energy code.
Minimum insulation R-values and window performance requirements for Climate Zone 5B in Boulder, Colorado.
| 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 5B requires precise load calculations. Upload your Boulder blueprint and get a professional Manual J report in 60 seconds— first report is FREE. Pre-loaded with Boulder's exact design temperatures (-7°F winter / 91°F summer).
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Official ASHRAE design temperatures for Boulder, used for accurate Manual J load calculations.
Minimum insulation and window requirements for Boulder per IECC 2021.
Energy Code: 2021 IECC
Upload your Boulder blueprint and get a professional Manual J load calculation using official Zone 5B design temperatures. First report is FREE.
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