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.
