What I built a number of years ago and still get great service from,
is a masonry stove with four vaulted chambers above the firebox which has a vaulted ceiling and the smoke goes up to the first chamber at the back.
The firebox is four feet deep by two wide and three high .
I have a 10 foot ceiling so the whole thing is about 8 feet high including a one foot high base that extends like a hearth in front of the stove.
I am a mason so I was able to pull it off ok.
What I wanted to say was the whole core is of 2 inch firebrick. I combined refractory and masonry cement which slows down the mortar and doesn't degrade.
ONce the core was built in firebrick the outside was cladded with natural stone to a height of 4 feet and the rest was parged .
THis thing requires a great deal of fuel but after 3 firings of about 2 garbage cans of wood the heat radiation and storage is unparalelled.
I burn mostly long wood and mostly softwood as that is what I have quantities of and it also gives the most heat.
My best advice to everyone is to use masonry as much as possible and shield any combustible matierials with mineral wool / drywall . Avoid metal.
If you are using a system with a steel pipe it it use stainless and set it up and screw it together and build around it with brick and mortar or stone that way if there are any voids they will have little impact.
Insured or not we don't want to burn the place down for the sake of heating the house.
My big masonry stove is a big job to feed but it gives intense long lasting heat and near complete combustion. You can hear the thing roaring as gasses burn up through the chambers.
There is about 15 feet of combustion chamber before the gasses hit the chimney so what comes out is very white, like steam.
Long story short , stacked chambers are ideal , especially when built of firebrick vaults.
The outside can be customized and there must be a second layer outside the firebrick , which will get dangerously hot.
Four inches is adequate outer skin but more can be added , 6 would be good too . The thicker that outer skin the longer it will take to heat up but the longer it will hold and re-radiate the heat.
Burning wood wide open !