Under the "Clearance Enclosed" section you will see an 8 inch
clearance as the pipe passes thru a wall horizontally. This means that you need 8 inches clearance from all around the pipe, a 19 inch round hole if you are using 3 inch diameter pipe.
The best way to minimize that 19 inch hole is to use a Z-Vent Wall Thimble, reducing the hole size to 7 inches. The Wal Thimble acts like a sleeve that your pipe will pass thru.
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Under the " Clearance Un-Enclosed" means that the pipe is not passing thru a ceiling, roof or wall. For example, if you have your appliance mounted in the Laundry room with the vent pipe going straight up, you only need 1 inch clearance. Then, when the pipe passes thru the ceiling, you would need to use a Firestop Support or Wall Thimble attached to the ceiling since the ceiling is considered an "Enclosed " area.
