Heat riser insulation idea?

[DrewInToledo]

Hello all. New guy here.

I apologize if this has already been entertained, but could spent ashed be used to fill the void between the inner and outer shells in the riser pipe instead of heavy materials?

Drew

[pa_friendly_guy]

Welcome Drew, glad you joined us. I have a small rocket cook stove [ there is a thread about it on here some place ] I used wood ashes as the insulation for that cooking unit. It works well. For the heat riser of a heating stove you have a much larger fire and much higher temperatures. Matt said the inside of his riser burned away after just a few fires. That would leave the wood ashes totally exposed with nothing holding them in place. For durability and longevity I would keep a much stronger material for the heat riser. I think you will find it will work much better than wood ashes.

[matt walker]

Good to see you on here Drew, welcome. I'll back up what Guy says, but I will add that wood ash mixed with clay can be used as a pretty low grade insulator for quick builds that you don't expect or care to last very long. I've read of folks using it with some success, but it seems it slumps and compresses over time, reducing it's insulation value. Still, probably a reasonable material for yard experiments.

[hpmer]

I use it for my builds, but the others are right; ashes by themselves will pack down over time and lose their effectiveness. The way I use them is to mix them with a clay slip and then use them as the mix for the core build. They will fire over time just like brick and I've found they work pretty well.

I've only built a few of these things (5or 6) so it's a bit anecdotal, but so far am pleased with the results.

That said mine are cook stoves and are not used every day, so Matt may be right about longevity if you're planning on firing it every day for heat.

I'm currently building one of Matt's barrel bbq's so this one will get more of a workout, but I won't have results for a while, so that doesn't help you at present with your decision.

[DrewInToledo]

Thank you for the kind replies. It will be quite a while before I make something for my home, but using ash will allow me to experiment at a lower cost.