This question has come up a lot. Look around on the forums for more info.
Check out this page on the forums: "
https://permies.com/forums/posts/list/40/2558 "
where some people talk about this:
http://www.iwilltry.org/b/build-a-rocket-stove-for-home-heating/
There are definitely more posts which address this idea.
Disclaimer, I'm not an expert; but anyway: this is what I seem to remember about the issue:
Truly this would be a 'massive rocket heater,' and not a 'rocket-mass-heater' --- why? I'll explain
At the heart of the general design of rocket-stoves, there is a 'heat-riser' (an internal chimney, inside the barrel). The hot gases burn up through this and then hit the barrel. The barrel acts like a radiator and cools the gases, which then drop down and out the exit. All of this creates a strong draft.
It is that strong draft which makes possible the horizontal exhaust system, around which an earthen-'mass' is constructed to reap heat. By the time the gases are exiting the system, they have 1) gone through a bunch of piping, the friction of which has already put quite a drag on the draft and 2) the gases have cooled down a lot (the heat from them has gone into warming the bench).
Now, for many rocket-mass-heaters it is recommended that the exhaust system finishes with some sort of a vertical chimney. The warm gases love to flow up the vertical chimney; This helps with the draft, as long as 1) there hasn't already been too much pipe with too much friction and more importantly 2) as long as the gases aren't already to cold. In other words, if the gases have already gone through the mass (which has reaped a lot of their heat), then they may be too cool to properly move up the chimney. So this all depends on, 1) what temperature the exhaust-gases are, relative to the outdoor air and 2) how long the chimney is.
If your chimney is too long, then the gases will cool too much before exiting, and this will screw up the draft.
In any case, you should be able to run a rocket-stove through a conventional chimney; that is, you might have to subtract the 'mass' from the equation. This way, you may not have a mass, but at least you'd have a super-efficient rocket-stove.