Find the serial number for an 80 percent annualized fuel utilization efficiency Lennox heating system beneath the top-front service panel. Remove the panel and look to the left of the cabinet to locate the system's serial number.
If the heating system is a 90 percent AFUE unit, check the blower deck for the serial number. The orientation of the heating system unit and the direction that the air flows through the unit also may change the location of the system's serial number within the internal cabinet.
You must use the serial number to register the system with Lennox; registering the product makes you eligible for free product information and offers. Lennox Elite and Merit heating systems may also be eligible for an extended 10-year warranty with their model and serial numbers. This warranty adds an additional five years to the basic parts and services warranty coverage.
The extended warranty is only available for matched heating systems. There are three different types of matched heating systems: furnace-only systems, packaged furnace and air conditioning systems, and split furnace and air conditioning systems. For the furnace-only and packaged system types, the customer only needs to supply the serial and model number of the unit. For split heating systems, the customer needs to supply the serial and model numbers of both units.