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.

I commend you for trying to keep the kiva style, it's a sacred design in that NM area.  
It might work to emulate the work of the acclaimed mr chickadee.  He quietly , serenely shows how to build a diminutive brick stove with local materials,,,,if you have clay in your soil nearby.  Fireclay would work too  
Check out his work please.  All of his craft is an invitation to think in a meditative manner. I hope you find some suitable solution

It might be possible to construct a 5-channel contraflow insert to fit in the available space.  This sounds like a very tricky proposition, however.

I am currently working through Axel Berberich's online course/tutorial (offered through Bosco di Ogigia) on building a pyrolyzing gasifier stove, using homemade precast refractory parts (and some metal bits, too).  My primary interest in his course is that he discusses somewhat peripherally the conversion of wood cook stoves to gasifier burners.  Old wood burning cook stoves in serviceable (if not pristine) condition are typically available in my area for between 100 and 200 USD, but sometimes can be had free for the hauling (I got a kitchen end heater that way - rolled it away on an appliance dolly!).  Anyway, I would suspect that you could, with care, make up molds for pieces to fit up into the existing fireplace's firebox and smoke chamber to define the contraflow channels.  Axel recommends a mix of high alumina refractory cement and vermiculite for the precast pieces.  One time molds might be made from scraps of wood, sheet metal flashing, cardboard mailing tubes or sonotubes, etc.   He glues the pieces together with a mix of fire clay and sand, similar to how most thermal mass heaters made from bricks are mortared together.  But, is all of this worth it?  I don't know.  It would be a reversible conversion, though, if done with care, so might do minimal if any violence to the architectural integrity of the house.

Another thought would be to make a firebox insert which converts it into more of a radiant fireplace, Rumford style.  That might be easier, and should get more heat out into the room.  There are lots of modern interpretations of Count Rumford's fireplace.  My recommendation is to chase down his book (I have found it on Archive,org in the past), give that a read, then see what some of the modern proponents have to say about it.  At least you'll understand the problem he was trying to solve (not so different from your inefficient fire place) and what he did to improve matters, and you can better assess the modern versions.  You could pre-cast some Rumfordizing parts, too, though fitting the traditional lintel and throat into the Kiva style fireplace might also be tricky.

Maggie writes,

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).

About 10 years ago, I attended a lecture at the Dorothy Day Center in Albuquerque, NM, where the original fireplace in the old adobe home was converted to a rocket mass heater within the previous decade (around 2005). In a wonderful spirit of sharing knowledge, the staff at the time gave me a tour of the entire system from indoor fire starting to ground-level clean-out to roof top vent. I highly recommend scheduling a field trip to see the system and understand the issues with the conversion. It is possible that the system was removed due to staff turnover and loss of rocket mass heater expertise over time. If you do schedule an appointment, please let us know what you find out.