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What is a Heating Degree Day?
A heating degree day is a statistic used to measure how cold a location has been relative to a baseline amount. It is calculated by subtracting the mean temperature for a day, and subtracting that number from 65F. For example, the average temperature in New York City on December 20, 2021 was 32F. Therefore, there were 33 heating days in NYC that calendar day.
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