Most furnaces require 4 inch vent pipe to be installed ... you can use pvc as long as it is rated for the temperature... there should be an obvious hole in the furnace where the enducer draft motor pushes the exhaust... if this is a upflow unit in the closet you will need to connect to the bell housing of the exhaust and start running your pipe up and out side .you will need double wall pipe rated for heat and or rated pvc if installing pvc... once outside make sure if on rood you have a roof jack for pipe to go through and a collar around pipe to keep water from running down and then a cap on pipe ....if it is a horizontal unit done the same way except your already in attic and don't have a as far to go it can run vertical and horizontal try to minimize your 90 degree turns and is best to keep it angled to prevent moisture from buiding up in pipe...
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Most furnaces require 4 inch vent pipe to be installed ... you can use pvc as long as it is rated for the temperature... there should be an obvious hole in the furnace where the enducer draft motor pushes the exhaust... if this is a upflow unit in the closet you will need to connect to the bell housing of the exhaust and start running your pipe up and out side .you will need double wall pipe rated for heat and or rated pvc if installing pvc... once outside make sure if on rood you have a roof jack for pipe to go through and a collar around pipe to keep water from running down and then a cap on pipe ....if it is a horizontal unit done the same way except your already in attic and don't have a as far to go it can run vertical and horizontal try to minimize your 90 degree turns and is best to keep it angled to prevent moisture from buiding up in pipe...