I hope to be building a furnace soon. I have a well pressure tank I can use for the shell. It has an OD of 22".
Initially I was thinking, a 12" bore, 1" hotface and 4" insulation refractory. But because of the size of this thing, I'll need a LOT of refractory which is going to be pretty expensive.
Now I won't skimp on the hotface, I still plan to use a 1" thick layer of 3000 degrees commercial refractory.. but I'm wondering if I could substitute the Kast-O-Lite 26 LI that I originally had in mind for the insulation layer, for say, fireclay (40 mesh Hawthorn bond) mixed with foam or sawdust. Would that hold up to cast iron temps? Fireclay is soooooo much cheaper! If fireclay alone isn't gonna cut it, would adding some aluminum oxide help? They sell it as abrasive at Harbor Freight.