Example of a typical free standing installation.

All stove installations would go through a protected wall and into an insulated chimney, or a masonry chimney. Once you pass through a combustible wall with an approved insulated or clay thimble you must continue to the termination point outside with insulated or masonry chimney and not switch back to double wall air insulated pipe for instance.

Can I reduce the clearance to combustibles?      Yes.

Air insulated double wall black pipe can be used to reduce the clearance to a combustible surface indoors.  This allows your black stove pipe to be installed closer than 18" to the combustible or non combustible surface.

Sheet metal or other non combustibles can be used to  reduce the clearance to a combustible wall. Use 1" copper pipe spacer to keep your 20ga. or heavier sheet metal spaced 1" off your combustible wall. This will allow you to reduce the stove clearance from 36" to 18" from a combustible wall.

Cathedral ceiling.

Less expensive 24ga. black stove pipe can be used on a top vent stove in a free standing installation all the way to the combustible ceiling / rafters where you must go through the ceiling / roof with insulated pipe to the end of the chimney. You can not switch back to single wall or double wall air insulated pipe. Use insulated pipe only. See instructions that come with the insulated chimney for roof installation clearances.