Question: I've talked to a few people who tell me I'm stuck with the 6" crock I have. What do you mean by knock out the crock. The 6" crock is cemented in through a brick wall- then a cinder block wall then into the chimney. The opening would need to be opened up to about 9". I guess using a long chisel or an hammer chisel with a long bit. However- how do you cement the new liner in and get a good seal at the chimney liner. I've posted this question other places on the net but haven't gotten an answer yet. Any help would be appreciate.Also- suppose I use the 8" stove pipe from the stove all the way up to the 6" liner. Then the restriction would be limited to the 2 foot length of horizontal liner. Would this make any difference? Answer: No- if you reduce to 6" anywhere- it's the same as doing it the whole way.Yes- either knock the old out and use masonry tools or hammer drill to enlarge. Then using same drill- enlarge the hole into the flue liner. Put lots of refractory cement into the hole- press the new crock or short piece of insulated chimney around it- and then reach inside with your hand and smooth out the cement. Apply more cement if needed to fill in the holes.