Number 2 fuel oil is a common, middle-distillate petroleum product that plays a significant role in both stationary heating and mobile transportation. This fuel is a refined component of crude oil, positioned between lighter products like gasoline and heavier oils like residual fuel. Its primary function is to provide highly efficient energy for residential and commercial heating systems, particularly in colder climates, and as a primary fuel for diesel engines.
Defining the Fuel and Its Characteristics
Number 2 fuel oil is classified as a middle-distillate, drawn off during the crude oil refining process after lighter products (such as gasoline and jet fuel) but before the heavier lubricants and residual oils. It possesses a high energy density, typically delivering approximately 139,500 British Thermal Units (BTUs) per gallon, making it an efficient source of heat and power.
The fuel’s viscosity allows it to flow easily through burner nozzles without requiring preheating, unlike heavier grades. Its flash point, the lowest temperature at which vapors ignite, is regulated to be at least 100 degrees Fahrenheit for safe storage and handling. Regulatory focus has led to the widespread adoption of Ultra-Low Sulfur Diesel (ULSD) and heating oil to minimize harmful emissions. No. 2 fuel oil is generally an amber-colored liquid with a kerosene-like odor.
Primary Applications and Usage Distinctions
The two most common applications for No. 2 fuel oil are as home heating oil and as diesel fuel for engines. As home heating oil, it is combusted in furnaces and boilers to heat residential and commercial buildings, a practice particularly prevalent in the Northeastern and Mid-Atlantic regions of the United States.
The chemical composition of No. 2 heating oil and No. 2 diesel fuel is nearly identical, originating from the same light gas oil cut in the refinery. The crucial distinction between them is regulatory and tax-based. Heating oil is not subject to road taxes because it is used exclusively off-road for stationary heating.
To enforce this tax exemption, heating oil and untaxed off-road diesel are dyed a bright red color, making them easily identifiable. Conversely, diesel fuel sold for use in on-road vehicles is taxed to fund highway infrastructure and is therefore left clear or slightly greenish in color. Using the lower-priced, red-dyed heating oil in a road vehicle is considered tax evasion and can result in substantial fines if discovered.
Comparison to Other Distillate Fuel Grades
The grading system for fuel oils, numbered 1 through 6, is based on a progression of increasing weight, viscosity, and boiling point. No. 2 fuel oil sits in the middle of the distillate range, providing a balance of energy density and manageable flow characteristics.
Immediately lighter is No. 1 fuel oil, which is closely related to kerosene and jet fuel. No. 1 oil is less viscous than No. 2, giving it a lower pour point and superior cold-weather performance. Because it resists gelling in extreme cold, No. 1 fuel oil is often blended with No. 2 in winterized formulas to ensure the fuel keeps flowing in outdoor storage tanks.
Heavier than No. 2 is No. 4 fuel oil, which is a blend of heavy distillates and sometimes residual stock. No. 4 oil is thicker and contains a higher energy content than No. 2, but it is primarily used in larger, commercial, or industrial burners that do not require the fuel to be preheated. The progression continues with even heavier residual oils, like No. 6, which are highly viscous and require significant heating before they can be pumped and burned.