### Calculation for Heating Season in Standard Units

Determine the average outdoor temperature per day during the heating season. This is called T-average.

Subtract the T-average from 18.3 degrees Celsius. This is the average heating required per day to keep the building at a comfortable temperature.

Multiply the average heating required per day by the number of days during the winter or heating season. The result is the heating degree days.

### Calculation for Heating Season in American units

Determine the average outdoor temperature per day during the heating season. This is called T-average.

Subtract the T-average from 65 degrees Fahrenheit. This is the average heating required per day to keep the building at a comfortable temperature.

Multiply the average heating required per day by the number of days during the winter or heating season.

### Calculation for Cooling Season in Standard Units

Determine the mean or average daily outdoor temperature during the cooling season. This is called T-average.

Subtract 18.3 degrees Celsius from the T-average.

Multiply the average cooling required per day by the number of days during the summer or cooling season.

### Calculation for Cooling Season in American units

Determine the mean or average daily outdoor temperature during the cooling season. This is called T-average.

Subtract 65 degrees Fahrenheit from the T-average.

Multiply the average cooling required per day by the number of days during the summer or cooling season.

## Things You Will Need

- Average outdoor temperature per day

## Tips

- If the desired room temperature is higher than 65 degrees Fahrenheit or 18.3 degrees Celsius, simply substitute the desired temperature into the equation for the degree-days result for that situation.
- "Encyclopedia of World Climatology" states that "the growing degree day is used by farmers as a guide for planting and estimating when a crop will be ready for harvest." The growing degree day equation is the base temperature of the crop to grow from the daily mean temperature. The number of days for which the average temperature is above the base temperature of the crop yields the growing season.