Find the model number, serial number and other important information about a Goodman furnace on its data tag, usually on or inside the door. Open the door on the upper compartment of the furnace to access the data tag.
The model number typically starts with "GM" and includes a series of letters and numbers to indicate the model of the furnace. Note that the model number is not the same thing as the serial number; the serial number is unique. If you cannot access the furnace, check the instruction manual or other documentation that came with the furnace to find the model number.