Looking for advise from RMH veterans

I'm making an all steel rocket style incinerator with a very wide/tall airtight cap feed tube so we can burn yard waste/trash and be a little more comfortable hanging out outdoors in the winter. I have been reading that draw is way better when the riser is insulated but also that a insulated steel riser also won't last. The pipe i have is 6 inches in diameter (15.25 cm) and about 1/8 inch thick (3 mm) I have some 7 inch chimney pipe I was thinking about putting around part or all of the riser and filling the gap with perlite or vermiculite. The riser is going into a 100lb propane tank with a few vent doors cut in it and a chimney out the bottom. Will my riser disintegrate if I fully insulate it an inch all the way around? What if I only partially insulate it?  I'm not looking to heat a bench or anything but I do want adequate draw and little or no smoke when I'm burning straight dry wood.

Hi AJ,   Welcome to the RMH forum.    I'm not sure what you mean by "a very wide/tall airtight cap feed tube". A typical rocket stove has a relatively short feed tube, has the same cross sectional area as the rest of the unit and is kept open to allow for draft. Perhaps a drawing would clarify.

I started out with an insulated heat riser made with a steel core and it lasted for maybe a year. It all depends on how much you use it and how hot you burn it. However, steel is destined to spall rather quickly (even stainless but lasts a bit longer) especially when insulated and therefore is not a good long term material for a heat riser. What you could do is add some clay slip to the perlite which many people (including myself) have done with good results and either let the metal core burn out or remove it carefully once the clay/perlite has set up after a firing or two. This was the standard low cost way to make a heat riser years back but innovation keeps moving us forward with better materials.

The best video I've seen to date is from Bigelow farm where he shows his metal insulated heat riser and its condition:  RMH Autopsy

Gerry Parent wrote:Hi AJ,   Welcome to the RMH forum.    I'm not sure what you mean by "a very wide/tall airtight cap feed tube". A typical rocket stove has a relatively short feed tube, has the same cross sectional area as the rest of the unit and is kept open to allow for draft. Perhaps a drawing would clarify.

I started out with an insulated heat riser made with a steel core and it lasted for maybe a year. It all depends on how much you use it and how hot you burn it. However, steel is destined to spall rather quickly (even stainless but lasts a bit longer) especially when insulated and therefore is not a good long term material for a heat riser. What you could do is add some clay slip to the perlite which many people (including myself) have done with good results and either let the metal core burn out or remove it carefully once the clay/perlite has set up after a firing or two. This was the standard low cost way to make a heat riser years back but innovation keeps moving us forward with better materials.

The best video I've seen to date is from Bigelow farm where he shows his metal insulated heat riser and its condition:  RMH Autopsy

Well maybe I'll just go with it uninsulated and see how it goes.  I can always cut the top off and add the chimney pipe, all my materials were free junk from farmer relatives.  If I were actually attempting to heat a home with it I would be much more fastidious in the planning.

Al, what you need is a 5 minute heat riser. And a brick base.

https://permies.com/t/92302/Ceramic-blanket-riser-board-core#759948

Your waste wood etc, magazine, you can make out of metal.

https://permies.com/t/54074/Rocket-Mag-heater-Rocket-Mag

The 5 minute riser does require an expensive piece of ceramic fiber blanket. For a scrounged, low-cost setup, I think a perlite-clay riser would be the best way to go. Get an outer shell of sheetmetal 4" larger in diameter than you want your system, so you end up with 2" thick walls in your riser. There are lots of descriptions of making a perlite-clay riser in the forum.

Since you are wanting just a way to keep warm while burning yard waste, I don't think a complete barrel is necessary, though at least a partial barrel over the riser would protect against escaping sparks. Perhaps setting a barrel on supports so the top half of the riser is covered by the barrel would be a good compromise between easy drafting and capturing radiant heat.

Making your burn tunnel out of brick instead of metal will help that last longer too.