In previous examples, we are assuming that the outside temperature remains the same for all 150 heating days in a season. This is not realistic, but it explains the method to calculate the HDD. In a more realistic example we need to find the temperature difference for each day and add all the temperature differences.

We will now look at Seasonal Heating Degree Days (HDD), which is the sum of temperature differences of ALL days - rather than just 1 day or 1 week - during which heating is required.

The table below provides Seasonal HDDs for selected places in the United States. The higher HDD indicates a higher heat loss and therefore, higher fuel requirements.

HDD is used to estimate the amount of energy required for residential space heating during a cool season, and the data are published in local newspapers or on the National Weather Service website.

Place | Degree Days |
---|---|

Birmingham, AL | 2,823 |

Anchorage, AK | 10,470 |

Barrow, AK | 19,893 |

Tucson, AZ | 1,578 |

Miami, FL | 155 |

Pittsburgh, PA | 5,829 |

State College, PA | 6,345 |

### Calculating Seasonal Heating Degree Days

To calculate Seasonal Heating Degree Days, use this formula:

Remember, in months where the average temperature is equal to or greater than 65, there will be no heating degree days, so the value for the month will be 0.