I have an old home (pre-1900) and bought an insulated liner kit etc for installing my families old Intrepid II VC stove. I am trying to reuse the old thimble in the masonry to avoid a good bit of limed mortar chiseling and re-bricking. The installation would go into the chimney/thimble horizontally. My issue is that the stove pipe would only be about 14 - 16" below the old white oak mantel. Clearances for single walled stove pipe are supposedly 18" and I am trying to avoid using double walled because of the cost. Could I use double walled for only the section from the thimble to my first bend (as the mantel only protrudes ~5")? The other option I was thinking about was using a stove pipe protector, but these say mainly used for vertical installations. Any help would be much appreciated.