Heating & Cooling Degree Days Calculator

Calculate heating degree days (HDD) and cooling degree days (CDD) from any location worldwide. Get 30-year climate averages for energy analysis.

Calculate Heating and Cooling Degree Days for any location worldwide. Enter a city name to automatically fetch historical weather data and compute average annual HDD/CDD based on 30-year climate normals or custom date ranges.

Typical base temperature: 65°F (18°C) for heating/cooling in US. Energy estimates are approximations - actual consumption depends on building efficiency, HVAC system, and occupant behavior.

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What are Heating & Cooling Degree Days?

Degree days are a measure of how much (and for how long) outdoor temperature deviates from a comfortable base temperature. Heating Degree Days (HDD) accumulate when temperatures fall below the base, indicating heating is needed. Cooling Degree Days (CDD) accumulate when temperatures rise above the base, indicating cooling is needed. Degree days correlate strongly with energy consumption and are used for: energy benchmarking, predicting utility bills, comparing buildings across climates, and sizing HVAC equipment. The standard base temperature is 65°F (18°C) in the US, assuming buildings don't need heating/cooling when outdoor temps are near 65°F.

Degree Day Formulas

Heating Degree Days (HDD)

HDD = max(0, T_base - T_avg)

Example: Base 65°F, Avg 45°F → HDD = 65 - 45 = 20 HDD

Cooling Degree Days (CDD)

CDD = max(0, T_avg - T_base)

Example: Base 65°F, Avg 80°F → CDD = 80 - 65 = 15 CDD

Practical Tips

Use the 30-year average for 'typical year' energy analysis and HVAC sizing
65°F/18°C base works for most buildings, but adjust for high internal gains
HDD/CDD correlate best with gas heating and electric AC consumption
For energy prediction: Energy ≈ HDD × Heat Loss Factor (Btu/HDD)
Historical 30-year average is the industry standard for climate normals
Combine with building square footage to calculate Energy Use Intensity (EUI)