Oil Burner Nozzles

A fuel oil burner nozzle does one job: deliver a precise mass of oil as a controlled spray of the right shape, at the right angle, so the burner air can burn it completely. Get the nozzle wrong and you get soot, unburnt oil on the tubes, flame impingement on the furnace wall and wasted fuel — all from a component the size of a thumbnail.

Unlike a process spray nozzle, an oil burner nozzle is rated by firing rate in gallons per hour at a reference pressure (almost always 100 psi), not by free flow at a chosen bar. That reference-based rating is the first thing to understand.

Firing Rate and Pressure

The GPH rating is fixed at 100 psi. Change the supply pressure and the actual firing rate shifts as the square root of the pressure ratio, exactly like any other pressure-fed nozzle:

actual GPH = rated GPH × sqrt(supply pressure / 100)

Raise the pump pressure and you fire more oil per hour; drop it and you fire less. This is why a burner’s firing rate is partly a nozzle property and partly a pump property, and why chasing a firing rate by cranking pump pressure degrades atomization.

Hollow, Solid and Semi-Solid Patterns

Hollow cone places the oil in a ring and is the common choice for most pressure atomizing oil burners, balancing flame stability with air entrainment.

Solid cone concentrates fuel toward the centre, used where a more compact flame is needed.

Semi-solid sits between the two and suits specific burner designs. The pattern must match the air register, because the air is what actually atomizes and mixes the fuel in most burner types — the nozzle supplies a well-formed oil sheet, the air does the rest.

Spray Angle Versus Furnace Geometry

Spray angle determines how far the flame reaches and where the oil sheet meets the combustion air. Common angles run from about 30 degrees (long, narrow flame) to 90 degrees (wide, short flame).

Too wide and the spray impinges on the furnace wall or tube bank, cooking oil onto the surface. Too narrow and the flame is long and lazy, with poor mixing and a soft, smoky burn. The correct angle is set by the furnace diameter and the burner throat geometry, not by preference.

Why Oversizing Fails

The instinct is to fit a larger nozzle “for more capacity.” But the burner air is sized for a given firing rate and pattern, and a larger nozzle simply dumps excess oil the air cannot burn. The visible symptoms — black smoke, sooted tubes, oily residue — are the furnace telling you the air side and the fuel side are no longer matched. The right fix is to match nozzle, pump pressure and burner air as a system.

Reference Specifications

Firing rates below are rated at the 100 psi reference. Atomization type and angle are the independent selection variables.

How to Select an Oil Burner Nozzle

• Firing rate required — sets the rated GPH at 100 psi; confirm the pump actually holds 100 psi at that load.
• Spray angle — fixed by furnace diameter and burner geometry, not by the operator.
• Atomization pattern — hollow, solid or semi-solid, matched to the air register.
• Oil grade and temperature — viscosity at the nozzle sets atomization quality; cold heavy oil atomizes poorly and soots.
• Whether the air side is matched — a nozzle change that is not matched to burner air just relocates the problem.
• Availability of the rating — work from the rated GPH at 100 psi, never the nominal thread size.

Frequently Asked Questions

My burner smokes after fitting a bigger nozzle — why? The new nozzle fires more oil than the burner air can burn. Match the nozzle firing rate to the burner, not just to the pump’s output.

Does raising pump pressure increase firing rate? Yes, by the square root of the pressure ratio, but it also degrades atomization past a point. Rate and atomization are coupled.

What spray angle should I use? The one the furnace geometry demands. Too wide impinges on the walls; too narrow gives a long, soft, smoky flame. It is not adjustable by feel.

Why does cold oil soot up the furnace? High viscosity at the nozzle gives poor atomization, so droplets are too large to burn cleanly. Heat the oil to its design viscosity before the nozzle.