To anyone in the Heating & A/C Business it is important to track Degree Days. Our business tracks with extremes of weather. An indication
of Harsh or Mild seasons is the Degree Day
heating, cooling degree days
Heating engineers who wanted a way to relate each
day's temperatures to the demand for fuel to heat buildings developed the concept
of heating degree days.
To calculate the heating degree days for a particular
day, find the day's average temperature by adding the day's high and low temperatures
and dividing by two. If the number is above 65, there are no heating degree
days that day. If the number is less than 65, subtract it from 65 to find the
number of heating degree days.
For example, if the day's high temperature is 60
and the low is 40, the average temperature is 50 degrees. 65 minus 50 is 15
heating degree days.
Cooling degree days are also based on the day's
average minus 65. They relate the day's temperature to the energy demands of
air conditioning. For example, if the day's high is 90 and the day's low is
70, the day's average is 80. 80 minus 65 is 15 cooling degree days.
Heating and cooling degree days can be used to relate
how much more or less you might spend on heating or air conditioning if you
move from one part of the country to another. Of course you'd have to take into
account how well insulated your new home will be in comparison to your old one
and the different costs of electricity, gas or heating oil. You could also use
records of past heating degree days to see if the money you've spent on insulation,
or a newer furnace or air conditioner is paying off. To do this, you'd also
need records of past energy use.
In general, the easiest way to obtain daily, monthly, or yearly heating degree
days or cooling degree days is from the Web site of the National
Weather Service office that covers the place you are interested in.
Here are examples
of annual average heating degree days (HDD) and cooling degree days (CDD) at
some places around the USA.