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ROCHESTER, N.Y. – Have you ever heard of a heating degree day? It is a meteorological statistic that is not often discussed, yet it plays an important role in understanding how cold weather affects heating demand.
A heating degree day, or HDD, measures how much heating is required based on outdoor temperatures. It provides a straightforward way to estimate energy needs by comparing daily temperatures to a standard baseline. In the United States, that baseline temperature is 65 degrees Fahrenheit, which represents the point at which most buildings typically no longer need heating.
So how is a heating degree day calculated? Let’s look at a typical winter day in Rochester as an example.
If the high temperature is 40 degrees Fahrenheit and the low is 20 degrees Fahrenheit, adding those two values and dividing by two results in an average daily temperature of 30 degrees. That average temperature is then subtracted from the 65 degree baseline. In this case, 65 minus 30 yields 35 heating degree days, indicating a substantial need for heating.
Heating degree days are often accumulated over a period of time, such as a month or an entire season. So far this season, Rochester has recorded more than 188 heating degree days, suggesting colder-than-normal conditions.
Heating degree days are widely used for energy planning, utility demand forecasting, and evaluating building efficiency. During the summer months, a similar calculation is used to measure cooling needs. This is known as a cooling degree day and reflects the demand for air conditioning during warmer weather.
Together, heating and cooling degree days provide a useful understanding how temperature patterns influence energy use throughout the year.
