Heating Degree Days (HDDs) are a unit of measure that indicates how mild or severe a heating season was or will be by comparing the Average Daily Temperature to the “Balance Point” which is the outside temperature below which heating is required. For example, assume there are 10 days in a month where the Average Daily Temperature is 10⁰F colder than the Balance Point and the rest of the days are above the Balance Point. For that month there will be 10 days x 10⁰F = 100 HDDs. Trying to calculate HDDs manually can be tricky, so fortunately there are historical and forecasted HDD datasets publicly available from websites like www.weatherdatadepot.com.
Comparing this HDD data to your boiler’s historical fuel consumption can provide excellent insight into how well your boiler system responds to the changing heating loads throughout the year. Your boiler’s fuel consumption should be heaviest during the coldest months with the most HDDs, and lightest during the months with the fewest HDDs.
By Luke Wonnell