a mass sans stove pipe

Has anyone constructed, if possible, a mass without using stove pipe? I was thinking if one could form walls out of concrete to channel the exhaust gas threw and lay flat rocks on top and seal up the cracks using cob, the possibilities to channel the exhaust gasses would be endless. I would think if the mass were constructed so there are more than one parallel channels with the rocks on top, the heat distribution would be more even. Attached is a cross-sectional.

I am not an expert, but I think I read somewhere that the exhaust gasses may have acidic substances in them that can erode bare concrete. Also, concrete gets tiny cracks in it, usually, especially over time. Tiny leaks of carbon monoxide-bearing gasses into your living space are something you want to avoid the chance of.

I'm only repeating stuff I think I remember reading, while hoping that somebody who knows more will reply with better informed info.

OK instead of concrete walls, how about flat rocks installed vertically? I was also thinking about plate steel but I don't think that would work. This is going to be partially buried in a dirt floor of a barn which probably won't be that air-tight, so I'm not too worried about CO. However detectors are cheap these days.

Hi Dan; Welcome to Permies!   And welcome to the wonderful world of Rocket science!

What you are describing is known as a stratification chamber, or a bell.
You could use concrete that far from the core but its permanent and will crack. It would need a complete cob covering.
A tried and true method is the Walker half barrel system. Your RMH   vents into a series of split in half length wise 55 gallon barrels.
Your chimney would come off the far end.
The barrels are contained by low clay brick walls and covered over with cob or cob and topped with flat rock.

Walker Half Barrel System - I'll check it out. Thanks.

http://eng.stove.ru/stati/eschyo_raz_o_sisteme_svobodnogo_dvijeniya_gazov_ili_predlojenie  A must read.