# How to Use Heating Degree Days to Determine Oil Consumption

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In each climatic region, temperature records are used to determine the heating degree days. The difference between 65 degrees F and the average temperature of a day corresponds to the degree days for that day. Adding up all the degree days for the entire heating season produces the annual heating degree days. You can use this number to calculate how many BTUs of heat you will need over the entire heating season.

• Determine your house's BTU loss per hour per degree difference. Obtaining an exact value requires a complex calculation that involves the size, shape, insulation characteristics and window configuration of your house. The Home Heat Loss Calculator from builditsolar.com (see Resources) provides instructions, examples and a user interface that can help you with the calculation. For a rough estimate, a well-insulated 1,000-square-foot house might lose 675 BTUs per hour per degree of temperature difference.

• Multiply your house's BTU loss per hour per degree difference by 24 to find the heat loss per day per degree of temperature difference. For example, 675 x 24 = 16,200.

• Multiply this number by the annual heating degree days for your region. In the United States, 5,000 can be used as an average value: 5,000 x 16,200 = 81,000,000 BTUs needed to heat your house for the entire heating season.

• Look up the heat content per unit of heating fuel that you are using. This information is available in the Heating Fuel Comparison Calculator from the U.S. Energy Information Administration (see Resources). According to this spreadsheet, one gallon of #2 heating oil contains 138,690 BTUs.

• Multiply the heat content by the efficiency (in decimal form) to determine the amount of usable heat per unit of fuel (this information is also available in the spreadsheet): 138,690 x 0.78 = 108,178 usable BTUs. However, if you know that your heating system has a certain efficiency rating, use this percentage instead.

• Divide your total BTU requirement by the available heat per unit of fuel: 81,000,000 / 108,178 = 749 gallons of heating oil required for the entire heating season.

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