Windham is in IECC Climate Zone 6A (Cold - Humid). Get accurate Manual J load calculations with official design temperatures for Windham.
Windham, Vermont falls within IECC Climate Zone 6A (Cold - Humid), a heating-dominated region with humid moisture conditions. HVAC contractors working in Windham must use the official ASHRAE design temperatures of -9°F (99% winter) and 89°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 6A is heating-dominated, insulation levels are critical. Windham 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 6A in Windham, Vermont.
| 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 6A requires precise load calculations. Upload your Windham blueprint and get a professional Manual J report in 60 seconds— first report is FREE. Pre-loaded with Windham's exact design temperatures (-9°F winter / 89°F summer).
Enter your ZIP code to confirm it's in Windham and get climate zone details.
Official ASHRAE design temperatures for Windham, used for accurate Manual J load calculations.
Minimum insulation and window requirements for Windham per IECC 2021.
Energy Code: 2021 IECC
Upload your Windham blueprint and get a professional Manual J load calculation using official Zone 6A design temperatures. First report is FREE.
Join 10,000+ Windham contractors who trust AutoHVAC