A degree day is a unit we use for measuring how cold (or hot) it has been over a 24-hour period. This degree day affects your fuel tank and helps us determine how much fuel you have burnt for that time period. Whenever the average temperature on a day is below 65° (the base temperature for measuring a degree day), you have a degree day.
For example, if on a given day the outdoor high temperature was 70° and the low was 50°, then the average temperature for that day was 60°. That is 5° less than the base temperature of 65°. Therefore, we count 5 degree days for that one-day period.
Now you might be thinking that each house doesn’t burn the same amount of fuel everyday and you would be correct. To effectively calculate your tank’s burn rate, we also need two more numbers.
The first is the tank’s ideal delivery gallons. Considering your tank size, usable gallons and reserve gallons is how we derive your ideal delivery amount. For a typical 275 gallon basement heating oil tank, the ideal delivery amount is generally 200 gallons.
The last number is called the K-factor. This is simply a number showing how fast a tank uses fuel. Like miles-per-gallon on your car, think of a K-factor as gallons per degree day. If your car gets 20 mpg, and you have a 10 gallon gas tank, you know you can go 200 miles. Likewise, if we know you burner runs at a 5 K-factor and your ideal fill is 200 gallons, we know you can go 1000 degree days between fills.