Talked to the lopi dealer today and he told me that the new lopis are burning so cleanly that a full stainless liner is not longer needed. They stated that you can and they frequently are just sliding them and using them even if the existing flue was 12x12. Thoughts on this? It would certainly make a new insert more affordable knowing I wouldn't have to pay the extra big chunk for the liner and install, but is this guy correct? Will it still burn effectively and safely?