A professionally conducted load calculation is the foundation of an effective system.
Goodman furnace exhaust pipe size.
Goodman 96 afue gas furnace has 2 pipe direct vent to outdoors.
Outdoor exhaust intake combustion pvc venting.
Traditional gas fired forced air furnaces produce hot combustion exhaust gasses and therefore need metal vent pipes or chimneys.
This determines the size of vent pipe fittings and flashing needed to install the vent system.
In contrast modern high efficiency condensing furnaces exhaust much cooler gasses and need only plastic pipe materials such as pvc cpvc or abs for their exhaust vents some high efficiency furnaces also include a plastic pipe for intake area and all types.
Sizing the equipment load requires the consideration of several factors.
Measure the diameter of the circular flange where the vent attaches at the back of the furnace.
Ceiling height construction window size and placement and dozens of other variables all need to be considered to properly size a heating and or cooling system.