Measure the diameter of the circular flange where the vent attaches at the back of the furnace.
Goodman furnace exhaust pipe size.
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.
Outdoor exhaust intake combustion pvc venting.
Sizing the equipment load requires the consideration of several factors.
Also known as the induced draft fan this one has a fan that is located on the end of the pipe.
Since the exhaust pipe is running on a sidewall the fan works together with the furnace.
When compared to the natural vent this one is more flexible although it is also costlier.
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.