Which factor most directly determines an oil burner rating?

• A. Nozzle size
• B. Electrical supply
• C. Duct diameter
• D. Color of the burner

Answer: (A)

Fuel flow rate determines the burner rating, and the nozzle size directly sets that flow. The oil nozzle orifice controls how much fuel oil can pass at a given pump pressure, so a larger nozzle allows more fuel to be sprayed and burned, increasing the burner's maximum output (rating). Electrical supply affects ignition and control circuits but doesn’t define the rating itself. Duct diameter influences air balance and venting requirements, not the actual fuel input rating. The color of the burner has no bearing on its rating.