I have this old blaze king insert. Long story short I am a mason and built my own fireplace just for occasional use. Then I started to burn in it every day, did that for a few years. 20 rick a year and still no heat. Got this insert last year, just slid it in and sealed the face plate. I checked it half way threw the year and cleaned it. I would love a new stove but its not in the budget. I can however swing a liner, a lower priced one. I used ACS creosote remover the second half the year. I have a 20ft. exterior chimney. The tiles are big 13x17 . I slid the insert out and climbed the roof to inspect the flue. I was supprised the tiles on the top half were really clean . The bottom half had some bulid up. The throat going from the dampner to the first tile is pretty nasty. The stove puts plenty of heat out and is in good shape. To my question it has a slot 4" x 14" on the top at the back. I am going to weld me a collar for either a 6" or 8' liner at the back. I would rather go 6 that way if I can afford another insert with in the next few years I can reuse my liner if its in good shape. Blaze king made some woodstoves similar to this one and i belive they used an 8" . Will 6"be to small. I was considering building a shelf below the smoke outlet. thanks chad