<P> The degree day system is based on the amount of fuel a customer has consumed between two or more deliveries and the high and low outdoor temperatures during the same period . A degree day is defined as one degree of temperature below 65 ° F in the average temperature of one day . In other words, to arrive at the number of degree days in one day, the official high and low temperatures for that day must be obtained . The two figures are then averaged, and the number of units this average is below 65 ° F is the number of degree days for that day . For example, if for Tuesday, 3 November, the high temperature is 70 ° F and the low is 54 ° F, the average is found by adding 70 and 54, which equals 124, and then dividing by 2 . The resultant figure is 62, and by subtracting 62 from 65, it is determined that there were three Fahrenheit degree days that day . </P> <P> The K factor is the number of degree days in any given period divided by the number of gallons of fuel oil used in a given period . Multiplying K degree - days per gallon by the number of gallon of usable fuel remaining in a tank gives the number of degree - days before a delivery is needed . </P>

When was oil first used to heat homes