Heating Degree Day Calculation
Degree Day – What Is It & How Is It Calculated
A degree day is a numerical value of how warm or cool the weather is overall for any given day. The colder the day the higher the value is. The warmer the day the lower the value is.
It is calculated by taking a median temperature of 65°. This is the temperature that most houses do not need energy assistance to keep warm or cool. Next, the average temperature for that day is subtracted from the median temperature. This value is how many Degree Days represent the current day’s weather.
For example, if the average temperature for today is 30°. Calculate 65°(median home temperature)-30°(current day’s average temperature) = 35 degree days.
This means that 35 degree days represent that particular days weather and temperature. Read below how we use this information.
How We Use Degree Days – K-Factor
We have several Degree Day “clocks” at our different locations that automatically take the median temperature and read the average temperature for the day and calculate it to give us the Degree Days for a given day. That daily value is entered into our fuel management computer software. This is a continuously running number that we add to every day.
When you get a delivery, our system records the actual Degree Day in which your delivery was made. Then at your next delivery our system records the Degree Day again, but this time it’s also looking back to the previous delivery to see how many Degree Days have passed between the two deliveries. The gallons delivered are also looked at. Our system then divides the number of Degree Days passed in the time frame by the gallons delivered. The result of the calculation is called a K-Factor. A K-Factor can be thought considered the “Miles Per Gallon” for your home’s energy usage. The higher your K-Factor the longer you can go between deliveries. The lower the K-Factor means you will need fuel in a short period of time.
For example, if the actual degree day on your previous delivery fill was 2500 and the next delivery fill was on degree day 3800 for 200 gallons, this means that you used 200 gallons of fuel over 1300 degree days. ( 1300 / 200 = 6.5 ). This is your home’s K-Factor or “Miles Per Gallon”.
The K-Factor then in turn is a value of how many Degree Days must pass in a day for your house to burn one gallon of Heating Fuel or Propane. If 35 “Degree Days” passed like our example above, 5.4 gallons of fuel were needed that day to maintain a comfortable temperature.
Our system uses your calculated K-Factor along with our daily entered Degree Days to predict, based on your own personal fuel use, when you would be due for an “Optimal” delivery. Usually when our system calculates that your tank will take approximately 80% of the tank’s capacity during a delivery.