Vermont Climate Zone Heating Degree Days Calculator
Estimate annual Heating Degree Days (HDD base 65°F) for Vermont locations. HDD values are used in HVAC system sizing, energy code compliance, and fuel consumption estimates.
Annual HDD base 65°F for selected location. You may override with a custom value.
Your thermostat setpoint. Default is 68°F.
Standard base is 65°F. Adjust if using a different base (e.g., 60°F for tight buildings).
Gas furnace ~80–98%, heat pump COP ~200–300%. Enter as percentage (e.g., 95 for 95% AFUE).
Overall heat loss coefficient. If unknown, leave blank for a rule-of-thumb estimate.
Formulas Used
1. HDD Base Adjustment (ASHRAE ratio method):
HDDT2 = HDD65 × (Tindoor − T2) / (Tindoor − 65)
2. Annual Heat Loss:
Qannual = UA × HDDadjusted × 24 hr/day
3. Annual Energy Required:
Erequired = Qannual / η (η = system efficiency as decimal)
4. Peak Design Heat Load:
Qpeak = UA × (Tindoor − Toutdoor,design)
5. Fuel Equivalents:
Natural gas: E ÷ 100,000 BTU/therm |
Heating oil: E ÷ 138,500 BTU/gal |
Propane: E ÷ 91,500 BTU/gal |
Electricity: E ÷ 3,412 BTU/kWh |
Firewood: E ÷ 20,000,000 BTU/cord
Assumptions & References
- HDD values are 30-year climate normals (NOAA/NCEI) for Vermont stations, base 65°F.
- IECC climate zones per 2021 IECC Table 301.1: Vermont spans Zones 5 (southern), 6 (central), and 7 (northern).
- 99% heating design temperatures from ASHRAE Fundamentals Handbook, Chapter 14.
- HDD base adjustment uses the linear ratio method per ASHRAE Fundamentals, Chapter 18.
- Rule-of-thumb UA of 0.25 BTU/hr·°F·ft² represents a moderately insulated Vermont home; actual UA should be calculated from a Manual J or energy model.
- Fuel heating values: natural gas 100,000 BTU/therm; No. 2 heating oil 138,500 BTU/gal; propane 91,500 BTU/gal; electricity 3,412 BTU/kWh; hardwood cord 20,000,000 BTU/cord (Efficiency Vermont).
- This calculator provides estimates only. For code compliance or equipment sizing, use ACCA Manual J and consult a licensed HVAC engineer.
- Vermont residential energy code requires compliance with IECC 2015 or later; commercial buildings follow ASHRAE 90.1.