I have built stove of sorts. It is 5 inch steel tube ran up into a 30 gallon water heater. Drawn pic below. I did not insulate riser. I know this may not be the most efficient design, but it it what I have for now.
My question is, is it worth it to cut it open and insulate the riser tube? If so can I use metal ductwork for form and pour in perlite. Or should I use a mixed up fire mortar, perlite mix and a form that will burn away?
I can't rebuild it. This is my heat for now. So I just want to make it more efficient if it will till spring.