RMH in 4'x4' ?

We're currently heating about 1800 square feet with a Napoleon wood stove and two cords of wood each winter. It sits on a 4' by 4' brick pad downstairs with a 6" chimney that runs straight up sixteen feet.

Has anyone built a rocket mass heater in such a small area? I could see running the exhaust to the sides of the barrel, but that would involve many more corners.

Next, could I continue using the chimney that goes straight up?

Finally, with all the cob used as thermal mass, how does one clean the exhaust pipes and replace metal parts that wear out?

From what I've learned, a footprint that size might benefit from a rocket/bell design.
Something like this @ Donkey's site -
http://donkey32.proboards.com/index.cgi?board=experiment&action=display&thread=40

Really great info, but a lot to read...

Maybe Kirk (donkey) can chime in and give a more informed answer.....