If you are replacing current system in the same location.
If are replacing current system in a new location, or adding a new system
A furnace uses gas and will have intake/exhaust piping and a gas line, in addition to refrigerant and drain lines coming from the furnace.
A air handler uses electricity and will have only the refrigerant and drain lines coming from the air handler.
An 80% gas furnace will have metal flu piping for exhaust.
A 90% furnace will have plastic (PVC) piping for it's exhaust.