Heating degree days (HDD) are way to quantify the intensity of heating needs over a period of time, presented at a seasonal scale. The HDD for a single day are calculated as 65°F minus mean daily temperature. So, a daily mean temperature of 55°F yields 10 HDD, providing a metric that can be related to energy demand to warm the building back to 65°F. 65°F is used as a basis for the HDD calculation because it is an outdoor temperature generally regarded as comfortable. In this tool, the HDD for each day is totaled across a season, and negative HDD values are not incorporated because HDD are only meant to quantify the time and intensity of outdoor temperatures below 65°F. The summer season in New Jersey does not typically require heating as mean daily summer temperatures are rarely lower than 65°F.

Climate observations and projection data provided by the Northeast Regional Climate Center at Cornell University through their Applied Climate Information System (ACIS, rcc-acis.org). The Localized Constructed Analog downscaling projections were obtained from the Scripps Institution of Oceanography (http://loca.ucsd.edu). Time periods are simulated using greenhouse gas emissions scenarios RCP 4.5 (moderate emissions) and RCP 8.5 (high emissions). The modeled data have been extracted from the U.S. National Oceanic and Atmospheric Administration's Applied Climate Information System and localized to New Jersey.