OEM Lennox Secondary Heat Exchanger Assembly — 36M77

The genuine OEM Lennox 36M77 secondary heat exchanger assembly (also referenced as R20284504) is the condensing-stage component in compatible high-efficiency Lennox gas furnaces. Mounted after the primary exchanger, it extracts additional heat from the flue gases until water vapor condenses out — the process that lets these furnaces reach 90%+ AFUE efficiency. It routes the cooled exhaust and the resulting condensate for safe removal while transferring that recovered heat into your home's air.

Common failure symptoms: Because the secondary exchanger constantly handles acidic condensate, it is prone to corrosion pinholes and cracks. Warning signs include condensate leaks around the furnace, water in the burner or inducer area, a corroded or perforated exchanger surface, weaker heating performance, pressure-switch or flame-sensor faults, and short cycling. A breach can leak combustion gases, so a CO alarm or visible corrosion calls for prompt replacement.

Why OEM matters for Lennox: The condensing exchanger is engineered from specific corrosion-resistant materials and formed to precise passages for proper draft, condensate flow, and heat recovery. The factory 36M77 assembly guarantees correct fit, sustained high-efficiency output, and warranty and safety compliance that generic parts cannot deliver. Choose genuine OEM Lennox to protect your furnace's efficiency and your family's safety.