The Degree Day System

Fuel is consumed for heating based on how cold the weather has been and for how long. Gault used this information to estimate when to deliver fuel to a customer, based on a unit called a DEGREE DAY. These Degree Days correspond to fuel consumption needs, so for delivery scheduling purposes, Gault tracks them each heating season, which the National Weather Service traditionally considers to run from September 1st, to May 31st.

What is a Degree Day?

A Degree Day is simply a unit for measuring how cold (or hot) it has been over a 24-hour period. Whenever the average (or mean) temperature is below 65°, you have a Degree Day. For example, if during a 24-hour period the high outdoor temperature was 70 degrees and the low was 50 degrees, then the average temperature for that day was 60 degrees - halfway between 70 and 50 degrees. This is 5 degrees less than the base temperature of 65°. Therefore, we can say that there were 5-degree days for the period.

Helpful definitions:

K–Factor — simply a number showing how fast a household uses fuel. Like miles per-gallon,
think of a k-factor as degree days per gallon.

USABLE D.D. — tells how many degree days can elapse before making the next delivery.

RESERVE — the safety reserve in a tank.