Fuel oil grades are generally based on viscosity (i.e., thickness or flow resistance), boiling point, and use. The federal Energy Information Administration (EIA) categorizes fuel oil as distillate (i.e., number 1, number 2, and number 4 fuel oil) or residual (number 5 and number 6 fuel oil). The following table describes each grade as defined in state regulations. Number 3 fuel oil is no longer widely used as a classification.
According to the federal Environmental Protection Agency (EPA), while heavier residual fuel oils contain significant amounts of ash, nitrogen, and sulfur, emissions from fuel oil combustion depend not only on the grade and composition of the fuel, but also on the (1) type and size of the boiler, (2) firing and loading practices, and (3) level of equipment maintenance. For more information, see Table 1.3-1 in EPA’s Compilation of Air Pollutant Emission Factors.
Fuel Oil Grades
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Grades
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Regulatory
Definition and Examples
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Number
1
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A
light distillate fuel oil intended for use in vaporizing pot-type burners.
Number 1 fuel oil is used primarily as fuel for portable outdoor stoves and
portable outdoor heaters.
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Number
2
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A
distillate fuel oil for use in atomizing-type burners for domestic heating or
for moderate capacity commercial-industrial burner units.
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Number
4
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A
fuel oil for commercial burner installations not equipped with preheating
facilities that is extensively used in industrial plants. This grade is
usually a blend of distillate and residual fuel stocks, but can be a heavy
distillate.
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Number
5
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A
residual fuel oil more viscous than number 4 distillate fuel for burners
capable of handling a more viscous product. Preheat may be necessary
depending upon equipment design and climatic conditions.
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Number
6
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A
high-viscosity fuel oil for commercial and industrial heating and power
generation. Preheating is required for satisfactory use. This grade includes
(1) heavy-grade residual fuel oil referred to as Bunker C fuel oil and (2)
Navy Special, a grade of residual fuel oil for use in steam powered vessels
in government service and in shore power plants.
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