how to calculate heating degree day hdd 
there are several ways to calculate hdd the more detailed a record of temperature data the more accurate the hdd calculation for all methods if the value for any given day is less than or equal to zero that day has zero hdd but if the value is positive that number represents the hdd on that day a similar measurement cooling degree day cdd reflects the amount of energy used to cool a home or business one caveat is that heating degree days are extremely localized heating and cooling needs vary greatly depending on the geographical region and further the average hdd in one building may not have the same impact as it does in the building next door due to differences in construction orientation relative to other buildings insulation sun exposure and the nature of the building s usage 