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Frequently Asked Questions About HDD & CDD & GDD
Answers
What are "HDD" and "CDD"?
HDD and CDD stand for "Heating Degree Days" and "Cooling Degree
Days." They are units of energy need based on a "comfortable" inside home temperature of 65 degrees. They are
calculated by taking the difference between 65 degrees (F) and the average outside temperature (F) for the day.
Examples: If the average temperature (high + low divided by two) is 65 degrees,
then there 0 (zero) HDD and CDD. If the average is 75, there were 10 cooling degree days (because you would have to
cool your house to get it back to 65). If the average for the day is 20, then there were 45 heating degree days
(because you would have to heat your house to bring it up to 65).
What are "GDD"?
The above concept for HDD and CDD was expanded by the agricultural industry to
represent comfortable growing for plants (Growing Degree Days). It is the same concept except the number is not 65; it might be 35,
45, or something else, depending on the type of plant.
What are "Normal Degree Days"?
Normal degree days simply refers to the average number of degree days (heating
or cooling or growing, etc.)
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