A simple hardface for a furnace.

It's a flu liner for a stove. It's petty much the same material as dense fire brick. I've used a slightly longer one for my new gas fired furnace.

It sits on a packed sand base, it has Ceramic wool around it, and the lid is fire cement and perlite.

It's survived a few melts at this point. It has quite a few cracks. But it was free so it's a win.