# Heating Degree Day (HDD)

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## Definition of 'Heating Degree Day (HDD)'

A heating degree day (HDD) is a measure of the amount of heat needed to raise the temperature of one degree Fahrenheit for one day. It is used to compare the severity of winters in different locations and to estimate the heating needs of buildings.

The formula for calculating HDD is:

HDD = (65°F - daily average temperature) * number of days

For example, if the average daily temperature in January is 35°F, then the HDD for that month would be (65°F - 35°F) * 31 days = 730 HDD.

HDDs are used to estimate the heating needs of buildings by multiplying the HDD for a given month by the building's heating coefficient. The heating coefficient is a measure of the amount of heat needed to raise the temperature of the building by one degree Fahrenheit.

For example, if a building has a heating coefficient of 1.0, then it would need 1.0 BTU of heat to raise the temperature by 1°F. If the HDD for January is 730, then the building would need 730 BTU of heat to keep the temperature at 65°F.

HDDs are also used to compare the severity of winters in different locations. For example, a city with an HDD of 1,000 would have a colder winter than a city with an HDD of 500.

Heating degree days are a valuable tool for estimating the heating needs of buildings and comparing the severity of winters in different locations.

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