OEM Lennox Burner Box w/ Manifold — 13U75

The genuine OEM Lennox 13U75 (factory part 603687-01) is a complete side-mount burner box assembly supplied with the gas manifold. It combines the burners and the fuel-delivery manifold into one factory-matched unit, distributing gas evenly to each burner and directing the flame into the heat exchanger for efficient, reliable heating. Because the manifold and orifices are pre-set to Lennox specifications, this assembly simplifies replacement while preserving correct combustion.

Common failure symptoms: A failing burner box or manifold can cause hard or delayed ignition, uneven or lifting flames, rumbling and popping noises, soot or a burnt smell, and repeated flame-sensor lockouts. Corrosion, cracked burner ports, blocked orifices, or a warped manifold all warrant replacement to maintain safe operation.

Why OEM matters: Lennox builds the 13U75 to exact orifice sizing, burner spacing, and manifold pressure specifications for your furnace model. Using the OEM assembly guarantees the correct gas flow, flame pattern, and clearances that protect the heat exchanger and sustain rated efficiency. Generic replacements risk misfiring, improper gas metering, and warranty issues. Fitting the genuine 13U75 returns your Lennox furnace to factory-designed performance and safety.