Attached pic looks like a cinder blocks. It goes down to the basement where it vents hot air from the oil burning system. We want to switch to a wood stove system. Chimney liners wont fit down this correct? It looks like stacked cinder blocks which have two holes in them a piece correct? So this would not have the correct space for a 6" chimney liner? Just thought I 'd ask you guys, I dont have much knowledge with this thnx