I found a grizzly insert model # fp12lex for sale for $200. I was wondering if anyone has any experience with this unit? It seems to be around 10yrs old and of the catalytic variety.I also have some questions that I have about installing this unit if I decide to buy it. 1.I'm sure that the catalytic unit will need to be replaced. How hard will these be to get? How much? 2.I have a rectangular flue, inside dimensions are 5 7/8" X 13".This unit has a 8" flue opening.Is it possible to adapt this unit to the flue with a flue liner? Where is a good place to buy these? I hope someone out there can help me. Thanks Jim