I have had a Buck 26000, since 1982. It came with refractory liners - covered the bottom and back and sides basically in the bottom corners and part way up the sides. The manual said they had to be used for burning coal with a coal grate. I never have used them because they cut down the size of the fire box considerably. I have never had any damage to the steel inside of the fire box that I can find (the entire fire box is surrounded by a second wall through which room air is forced by the fan, that is, a heat exchanger) I am just wondering though, if the stove wood retain heat longer if they were installed. It seems all the new EPA cert. stoves have liners.