Fuel Oils

Fuel oils are hydrocarbon mixtures obtained from crude petroleum by refining processes. They may be divided in the following six classes or grades:

1. No. 1 fuel oil for vaporizing pot-type and other burners designed for this fuel

2. No. 2 fuel oil for general-purpose domestic heating not re­quiring a lighter No. 1 oil

3. No. 3 fuel oil (obsolete since 1948)

4. No. 4 fuel oil for installations not equipped for preheating

5. No. 5 fuel oil for installations equipped for preheating

6. No. 6 fuel oil for burner installations equipped for preheating with a high-viscosity fuel

This classification of fuel oils is based on several characteristics, including: (1) viscosity, (2) flash point, (3) pour point, (4) ash con­tent, (5) carbon residues, and (6) water and sediment content. All





TYPICALTANK TRUCK INSTALLATIONS using containers of less than 125 gallons water capacity, ICC only, ASME system requires 5 ft spacing instead of 3 feet.


Fuel Oils

/ AT




"A" = minimum distance of 3 feet "B" = minimum distance of 10 feet "C" = minimum distance of 25 feet "D" = minimum distance of 50 feet


UNDERGROUND CONTAINERS minimum depth-6 inches




Fuel Oils


подпись: not to scaleNOTE. This distance may be reduced to not less than 10 feet for a single container of 1200 gallons water capacity or less providing the container is at least 25 feet from another container or of more than 125 gallons water capacity.

Figure 5-1 Suggested clearances for LP gas cylinders and Storage tanks. (Courtesy National LP Gas Association.)

Fuel Oils

To ensure an adequate supply of gas in each. (Courtesy National LP Gas Association)

These characteristics are important to consider when selecting a fuel

Oil. For example, the water content will determine its suitability for outdoor storage. A low viscosity indicates a fuel oil with good flow characteristics.

No. 1 fuel oil has the lowest viscosity (1.4-2.2). This is a distillate oil used in atomizing and similar burners because it can be easily broken down into small droplets.

No. 2 fuel oil is a distillate oil used in domestic oil burners that do not require preheating. It is slightly heavier than a No. 1 fuel oil. No. 4 fuel oil is slightly heavier than No. 2 and will work in some oil burners without preheating.

No. 2 and No. 4 fuel oils contain the highest ash content (0.10 to

0. 50 percent by weight, respectively). The other grades contain lit­tle or no ash. Although slagging (i. e., the formation of noncom­bustible deposits) is commonly associated with solid fuels such as

Grade or Type



No. 1 oil



No. 2 oil



No. 3 oil



No. 4 oil



No. 5 oil



No. 6 oil



Natural gas

Cubic foot



Cubic foot



Cubic foot


Courtesy Honeywell Tradeline Controls

Coal, this problem also occurs in oil-burning equipment (see Ash, Slag, and Clinker Formation later in this chapter).

No. 5 and No. 6 (or Bunker C) fuel oils are heavier than the other grades and require preheating. In automatically operated oil burners, the preheating of the fuel oil must be completed before it is delivered for combustion. When the fuel oil has reached a suitable atomizing temperature, the preheating is considered completed.

PS 300 and PS 400 are heating oils used on the West Coast. They roughly correspond to No. 5 and No. 6 fuel oils, respectively. PS 300 is the lighter of the two and is used primarily for domestic heat­ing purposes. PS 400 is heavier, requires preheating, and is used for industrial purposes.

The grade of fuel oil to be used in an oil burner is specified by the manufacturer. This should also be stipulated on the label of the Underwriters Laboratories, Inc. (UL), and Underwriters’ Lab­oratories of Canada. Table 5-3 compares the Btu content of the principal fuel oils.

Posted in Audel HVAC Fundamentals Volume 1 Heating Systems, Furnaces, and Boilers