can you turn a kiva fireplace into a rocket mass heater?

I live in Santa Fe, which is apparently the only place in the world with kiva fireplaces - of which I have 5!! Since fireplaces are such woefully inefficient ways to heat a space and I would really like to heat with our local wood, I have been looking but am unable to find any information about the possibility of converting them to a more efficient system. I'm wondering if I could build some kind of small masonry heater system into the firebox using firebrick, or built a small rocket mass heater into the firebox using cob and such, or else cob (maybe sand and then cob) around a wood stove inserted in (with the proper pipe inserted inside the chimney). Any ideas from someone with expertise? Thank you!

Hi Maggie,

To use the existing structure as a bell of a masonry heater you would have to remove everything that is inside and make sure that your chimney exit is close to the ground. It's rather impossible without disassembling entire fireplace. If preserving the fireplace is the objective then fitting a very small masonry heater would not work, because it would be still way too big to fit there. Using some insert may improve things a little, but only a little (with better combustion), because the masonry heaters are efficient due to heat being extracted from the exhaust by the mass.
In this case I recommend to take it apart and build a masonry heater from scratch with a bell in the shape of the kiva. It will be easier than trying to adapt something to a different function. We will guide you!

Can modification's be made to the Kiva?
Enlarging the bell portion?  
Can the exhaust piping be brought down to near floor level?  

A smaller batchbox (5") could be built out front, perhaps using the new design Shorty core.
It needs a sealed "bell" behind it where the exhaust is collected near floor level.
Brick can be used for the bell, and safely covered with cob to blend into what is left of the original Kiva body.


Your idea of using a standard metal box stove and covering it with cob is proven to not last.
The metal gets too hot and starts warping.