How To Calculate Degree Days Heating

Heating Degree Days Formula:

\[ HDD = \sum \max(65 - T_{avg}, 0) \]

Heating Degree Days (HDD):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What Are Heating Degree Days?

Heating Degree Days (HDD) are a measurement designed to quantify the demand for energy needed to heat a building. They are calculated as the sum of daily differences between a base temperature (typically 65°F) and the average outdoor temperature when the outdoor temperature is below the base.

2. How Does the Calculator Work?

The calculator uses the HDD formula:

\[ HDD = \sum \max(65 - T_{avg}, 0) \]

Where:

\( HDD \) — Heating Degree Days (degree-days)
\( T_{avg} \) — Average daily temperature (°F)
65 — Base temperature for heating (°F)
max() — Ensures only positive values are counted
∑ — Summed over the specified period

Explanation: When the average temperature is below 65°F, heating is typically required. The greater the difference from 65°F, the more heating energy is needed.

3. Importance of HDD Calculation

Details: HDD is crucial for energy management, utility planning, agricultural planning, and climate analysis. It helps estimate heating fuel requirements and compare energy consumption across different periods and locations.

4. Using the Calculator

Tips: Enter the average temperature in °F and the number of days for calculation. For multiple days with different temperatures, calculate each day separately and sum the results.

5. Frequently Asked Questions (FAQ)

Q1: Why is 65°F used as the base temperature?
A: 65°F (18.3°C) is considered the temperature below which buildings typically require heating to maintain comfortable indoor conditions.

Q2: Can I use Celsius instead of Fahrenheit?
A: Yes, but the base temperature would be 18.3°C instead of 65°F. Make sure all temperature values use the same unit system.

Q3: What's the difference between HDD and CDD?
A: HDD measures heating demand when temperatures are below the base, while Cooling Degree Days (CDD) measure cooling demand when temperatures are above the base.

Q4: How accurate is HDD for energy estimation?
A: HDD provides a good estimate for comparative analysis, but actual energy consumption depends on building insulation, occupant behavior, and heating system efficiency.

Q5: Can HDD be negative?
A: No, the max() function ensures HDD values are always zero or positive. When temperatures are above the base, HDD = 0.