I have a chimney with the 8- 1/2 x 13 terra-cotta flue liners and of course a 6" insulated liner won't fit. The chimney is 13' tall but only the the upper 6' has flue liners. How does everyone break these out . I haven't bought anything yet (insert or liner), I looked at the oval liner, how would you ever clean that? Still in the planning stages here