S636 CPVC vent pipe clearance to combustibles

Anyone use PVC or CPCV vent pipe on a mod/con and have it in contact with wood or combustibles. I had System 636 CPVC installed following manufacturers manual when by house was under construction but did not have gas yet. I used this because it is classified as Type BH Class IIB vent, suitable for use on appliances with flue gas temperatures up to and including 90ºC (194ºF) and has a 0” clearance to combustibles. Now that I am looking at different boilers I find they all have different clearances to combustibles for the vent. Some have 0” some have 1/2” and others have 1” clearance around combustibles also some say do not insulate as the temperature will damage the pipe and some say to insulate if it passes through a unheated space others say only leave the first 3ft exposed and must be CPVC. In my installation it is ran in a chase from the basement to the roof there is clearance around the pipe except in two places between the 1st and 2nd floor it touches wood a there is insulation around it at the attic floor. Has any had an installation where the vent is in a chase or touching combustibles any problems with over heating pipe or different manufacturers having different stack temps. I would think if they can be used with PVC rated at 140f than CPVC with a 190f rating should not be a problem especially if the pipe manufacturers approve it with 0” clearance to combustibles .