For a day with a high of 38°F and a low of 20°F, which Heating Degree Day (HDD) value is correct?

For a day with a high of 38°F and a low of 20°F, which Heating Degree Day (HDD) value is correct?

• A. 29 Heating Degree Days
• B. 36 Heating Degree Days
• C. 65 Heating Degree Days
• D. 58 Heating Degree Days

Answer: (B)

Heating Degree Days measure how much a day’s average temperature falls below a base temperature (typically 65°F) to estimate heating needs. First find the daily average: (38 + 20) / 2 = 29°F. Then subtract that from the base: 65 − 29 = 36 HDD. Since the average is well below 65°, you get a positive HDD value of 36 for the day. If you used a different method (like subtracting the high or the low from 65, or using a different base), you’d get other numbers, not 36.

Heating Degree Days measure how much a day’s average temperature falls below a base temperature (typically 65°F) to estimate heating needs.

First find the daily average: (38 + 20) / 2 = 29°F. Then subtract that from the base: 65 − 29 = 36 HDD. Since the average is well below 65°, you get a positive HDD value of 36 for the day.

If you used a different method (like subtracting the high or the low from 65, or using a different base), you’d get other numbers, not 36.