The model and serial numbers of each of the Lennox company's furnaces is visible inside the top-front service panel of the furnace. The model and serial numbers are located by looking to the left of the interior cabinet or the top of the blower deck, depending on the furnace style.
The exact location of the model and serial number information depends on whether the unit is rated as 80 percent or 90 percent annual fuel usage efficiency. The horizontal or vertical orientation and flow direction of the furnace may also impact the location of the information, but it is present somewhere on every Lennox unit. The Lennox website provides a diagram as a popup for customers who need extra help finding this information.
Lennox serial numbers contain information on the series type; the unit's capacity for heating and cooling, as appropriate; the dash type; and the unit's power characteristics. In older units, the power rating is measured in British thermal units. Modern numbers have an equivalency rating, but it is not an exact comparison. A single dash before an additional numeral at the end of a serial number indicates a minor engineering change in the model type that was insufficient to warrant a whole new series.