Heat riser material

Can chimney clay liners be used for heat risers in rocket heaters?

No, they won't last. They are made to stand high heat, but only gradual changes in temperature. People who have used them have found that the flue liners cracked soon. They may stabilize in their cracked state, but might also fall down, probably during a hot fire.

It all depends which ones.

If it's good fireclay, with tons of chamotte or alumina, they could be fine.

I'm still in the testing phase with the batch workshop heater.

220mm diameter chimney elements from tona.

They cracked. But are stable.  There's one big crack facing the port, which seems to have the edges melted or abraded. While nothing else than gases and fly ash reaches there. This one worries me.

I'm starting my second heating season.

They can be used, imho, in the upper part of a heat riser. with IFB in the lower part.

Let say, 50cm IFB, and 100cm chimney liners.