Oil Appliance Safety

How Oil Burners Work

Oil-fired heating appliances use a pressure-atomizing gun-type burner to convert liquid heating oil (No. 2 fuel oil) into a fine mist that mixes with air and ignites. Unlike gas burners that simply mix gaseous fuel with air, oil burners must mechanically atomize the liquid fuel into droplets small enough to vaporize and burn completely.

The major components of a gun-type oil burner are:

Fuel pump: Draws oil from the storage tank and pressurizes it to 100-150 psi (depending on the manufacturer's specification). Most residential oil burners operate at 100 psi pump pressure. Some high-efficiency units and commercial burners use higher pressures up to 150 psi for finer atomization.

Nozzle: The precision component that atomizes the pressurized oil into a spray pattern. The nozzle contains a small orifice and internal swirl chamber that breaks the oil into a cone of fine droplets.

Ignition transformer: Provides a high-voltage spark (typically 10,000 volts) across the electrode tips to ignite the oil mist. The electrodes must be properly positioned relative to the nozzle spray pattern.

Air handling system: A blower wheel and air tube deliver combustion air to the flame. An adjustable air band (or air shutter) controls the volume of air entering the combustion chamber. Proper air adjustment is critical for clean, efficient combustion.

Cad cell (flame detector): A cadmium sulfide photocell that detects the presence of flame by sensing light. If the cad cell does not detect flame within the safety timing period (typically 15-45 seconds), the primary control locks out the burner.

Nozzle Selection

The nozzle is specified by three characteristics: flow rate, spray angle, and spray pattern. Getting the nozzle wrong is one of the most common causes of poor oil combustion and elevated CO.

Flow rate is measured in gallons per hour (GPH) at the rated pump pressure (usually 100 psi). Common residential sizes range from 0.50 GPH to 1.50 GPH. The correct nozzle size is determined by the appliance manufacturer and is listed on the nameplate or in the installation manual. A nozzle that is too large over-fires the appliance. A nozzle that is too small under-fires it.

To calculate the BTU input from the nozzle flow rate:

BTU/hr = GPH x 140,000 BTU per gallon

For example, a 0.85 GPH nozzle at 100 psi delivers: 0.85 x 140,000 = 119,000 BTU/hr input.

Spray angle ranges from 30 to 90 degrees. The angle must match the combustion chamber shape and size. A narrow angle (30-45 degrees) is used for long, narrow chambers. A wide angle (70-90 degrees) is used for short, wide chambers. An incorrect spray angle causes flame impingement on chamber walls, producing soot and CO.

Spray pattern describes the shape of the spray cone:

• Hollow cone (Type A): Oil is concentrated at the outer edge of the cone. Used for smaller nozzle sizes (below 1.00 GPH) because it provides better atomization at low flow rates.
• Solid cone (Type B): Oil is distributed throughout the entire cone. Used for larger nozzle sizes and when the combustion chamber requires uniform flame distribution.
• Semi-solid (Type SS): A compromise between hollow and solid. Used for mid-range sizes.

Oil burners atomize fuel at 100-150 psi pump pressure through a precision nozzle specified by flow rate (GPH), spray angle (30-90 degrees), and spray pattern (hollow, solid, or semi-solid). The nozzle must match the manufacturer's specification exactly. No. 2 fuel oil contains approximately 140,000 BTU per gallon.