text: It's used for estimating fuel costs.\n\nEach town has an average number of heating degree days for the winter and average number of cooling degree days for the summer.\n\nWith those averages, you can calculate how long the air conditioner or heater will run for the year and then calculate the fuel costs.\n\n\n\nYou can calculate it from the average temperature each day.\n\nExample:\nAverage temperature for Jan. 1 is 30°F.\n65°F - 30°F = 35°F\n\nJan 1 is one day, so 35° difference * 1 day = 35 heating degree days\n\n\nAverage temperature for Jan. 2 is 35°F.\n65°F - 35°F = 30°F\n\nJan 2 is one day, so 30° difference * 1 day = 30 heating degree days\n\nYou do this for every of the year and add it up.\n\nJan 1 = 35 heating degree days\nJan 2 = 30 heating degree days\nJan 3 = \nJan 4 = \n\nAdd it all up and you get the number of heating degree days for the winter.