Interior Vertical - Roof Exit - You must maintain a 3-inch clearance between the pipe and a combustible wall for the entire interior run of the pipe. Also, if the total vertical run is 10 feet or more, then 4-inch pellet vent must be used. No exceptions!
** This information is generalized for use on all Thelin Pellet Heaters. Refer to your models installation and operating manual for information specific to your model.