There's also a variation on the Dakota pit stove with a longer chimney under the pot, sometimes called a "fox stove."
And ancient furnaces were often of the L-shaped configuration, with a LARGE firebox containing the bricks, ceramic crafts, metal for smelting, or whatever else was the target of the heat.
Even a "chimanea" might be considered as a kind of jug-stove or proto-rocket.
This has gotten kinda long, but I felt like chiming in on the definition of "rocket," and since it's an evolving term I ended up writing quite a lot.
The Permies members have started using the term "rocket mass heater" in preference for "rocket stove
" since it is more specific.
However, I would say that "rocket mass heater" is still a subset of "rocket stove
Since we cannot force people
who invented the term to stop using it for the entire range of their inventions, it seems a little pointless to demand "correct" usage of late-comers to the field.
If you are aware of the distinction, and wish to discuss the L-style cooking rockets, perhaps "rocket cook-stove" would be a short but specific term to use.
If the heater does not have a masonry or earth or water thermal mass, it's definitely not a rocket "Mass Heater."
Prototypes for low-mass or no-mass heaters
with the J- or L-shape made from thick steel, generally very short-lived in actual use. But I might call these a "rocket radiant heater," or a "hybrid rocket experiment." "Rocket wood stove
" just seems likely to be confusing.
What is not a rocket?
If it does not contain any insulation of any kind, and if it does not have a vertical smoke-burning part of the firebox (internal chimney or "heat riser"), someone has radically mis-understood the rocket concept.
I allow a little bit of leeway for Matt Walker's "riserless core," since it derived from rocket experiments, however I think he is heading back away from rockets toward baffled wood
stoves and cook stoves.
I don't imagine other tinkerers can make clean-burning adaptations of his designs without your own emissions meter to confirm success.
"Rocket" does not simply mean clean-burning stove, or firebox for a masonry heater, or bouquet of flames. It refers to a specific set of design paths.
As I understand it, the word "rocket" came into use among the researchers playing with this stuff in the 1970s, both as a reference to space-age concepts and insulation materials now available, and to the "whooshing" sound the fire makes when traveling fast through the constrained tube. (You can get similar sounds from a bonfire but it takes a lot more fuel.) Jet engines actually use some similar concepts, only with an air scoop instead of a thermal siphon.
The common denominator for rocket stove
design seems to be a vertical, insulated "heat riser" or internal chimney, which helps to burn the smoke and concentrate the heat of the flame before it is directed toward the functional target. You can have a rocket that heats water, cooks food, heats a thermal mass, warms an oven, or even one that just incinerates things and wastes a lot of heat.
Most rocket cookstoves worthy of the name include some kind of insulation, as do rocket mass heaters and rocket masonry stoves/cookstoves.
To work a different angle, if we are only talking about masonry, mass, or "accumulation" heaters, would we use the word "stove"?
Masonry heaters are often called masonry stoves. In Europe the category is sometimes called "accumulation stoves" or "accumulation heaters," or some variation. There are many masonry heaters that also are used for cooking, or especially for baking, including an oven above the heater's fire box. Because even the large-mass accumulation heaters generally heat in line-of-sight or by direct contact, they are sometimes considered stoves or radiant heaters rather than "furnaces"... a category described elsewhere.
With these mass/accumulation heaters, the exhaust from the fire will be passed through heat-exchange channels or bells (stratification chambers) for heat collection. It is not just ecological or efficient, but CRITICAL for safety that the fire burn very clean. A dirty, smoky fire will cause the mass to "accumulate" creosote as it stores heat, becoming a fire hazard, and necessitating frequent, expensive, and destructive cleaning.
We have now heard about 2 "rocket mass heaters" that were designed outside the proven parameters, which accumulated creosote. The owners reported two chimney fires in a single heating season, and are now troubleshooting their heater for unintended design errors. Luckily, both owners had used relatively good chimney construction, which prevented the chimney fire from burning down their house.
If you want efficient heat, and especially if you want to store that heat overnight, the smoke MUST be burned as completely as possible.
Therefore with most masonry heaters, mass heaters, or accumulation heaters, including masonry cookstoves, you see a big emphasis on a clean-burning firebox, and on proper balancing of draft and mass so that the fire runs at roughly the speed it was designed to run.
In the context of metal used (inappropriately) in the firebox, the reason the ambiguity of "rocket stove" pushes some people's buttons is that many people get the metal firebox idea from "rocket stoves" designed for cooking.
People who design "clean-burning" or "efficient" rocket cookstoves often have lower standards than we cold-climate designers would consider acceptable for an indoor heater.
Rocket cook-stove gurus may declare success if they reduce the smoke even slightly compared with an open hearth, campfire, or barbecue pit. The goal of smoke-free or soot-free cooking may be sacrificed in favor of other goals like extremely low cost, portable/camp stoves, convenient cooking height, etc. Because these outdoor cookstoves often have not even a chimney, the accumulation of soot and creosote, or the occasional "chimney fire" where this creosote burns along with the fresh wood, is not a big concern for the builders.
The smallest of these "rocket stoves" are toys or models rather than stoves - made with two steel cans, to demonstrate the chimney effect, or perhaps 3 or 4 cans to create an insulation gap which may be filled with air, perlite, or wood ash
While these micro "stoves" can burn slightly cleaner than a smoldering stick of wood, they are rarely smoke-free enough for indoor cooking. Fire and insulation simply don't scale well down to that small size.
Larger, institutional models of rocket stove, and better-insulated camp stoves such as the "jug stove" or termite-mound tea stoves, can burn a bit cleaner.
I have not personally seen one that burns clean enough that it would never leave soot on the bottom of the pot or cook plate, but it is possible they may exist somewhere.
I have also not personally seen an L-style rocket firebox that burned clean enough to power a creosote-free heat-exchange for a mass heater, without also dumping smoke into the room.
Batch box "rockets" without a proper door and secondary air tend to smoke out both ends. Hybrids between two different designs can get ugly, quickly.
It has become very common to see people learning about these relatively primitive, cooking "rocket stoves," and then hear about the "rocket mass heater
," and simply try to attach a mass to their cookstove's exhaust. They often do not realize they are leaping from one design path to another, or that there are a LOT of prior examples and information available to avoid repeating known errors.
This is kind of like living with bicycles, hearing about cars and semi-trucks, and trying to put together a trailer hitch that will allow a rickshaw "engine" to pull a semi-tractor's trailer load.
In the case of the bicycle, the most likely failure mode is that you will not go anywhere, and will do a lot of extra work for no gain. You might manage to crush yourself, but it's unlikely you would crush others.
In the case of mis-matched firebox and heating load, the most likely failure modes involve smoke in the home, creosote in the mass, and significant dangers to health and longevity for both the occupants and the building.
It is possible for one bad failure with a DIY indoor heater to wipe out a whole branch of the family line.
It is also possible, and far more likely, for a problem to smolder undetected by the original designer, only to pop up and create a problem for subsequent generations. Or in the most awkward season; most masonry materials can't be properly built or repaired in below-freezing temperatures.
I have witnessed a few near misses, where Grandpa's old wood stove installation was slowly charring roof purlins behind its metal shield. If Grandson had simply insulated the roof (as he intended), instead of also replacing the stove with an incidentally larger chimney, he may have lost the whole building within a year.
Steel well-casing is not a chimney "upgrade," for many reasons. Neither galvanized nor steel ducting is a proper chimney liner.
The word "rocket" does not IN ANY WAY relieve you of responsibility to take precautions.
Such as appropriate clearances and heat shielding, against the possibility of a chimney fire.
It is an unfortunate artifact of English usage that the words "you can" are often used generically, to mean "it is possible" or "someone once did." They can be misleading if taken personally, since "you" may not have favorable skills, materials, understanding, or the right situation.
"You can" build a rocket stove with metal (as in rocket cookstove, assuming you have the metal skills to operate a can opener, and don't mind re-building every few weeks/months of heavy use).
"You can" build a rocket mass heater
which will give clean, efficient heat for decades (if you personally take the time to learn a few basic masonry skills, and research and follow a proven design. "You" careful farmers may actually have better results than some of "you" trained engineers, because "you" farmers may be less tempted to alter the proven design with no experience
However, I doubt "you can" build a durable, efficient, smoke-free, safe-to-operate rocket mass heater
with metal in the firebox.
Might happen some day, but the amount of energy that will go into obtaining and working those metals may well exceed the entire lifetime energy savings of the "efficient" stove design.
"Someone once did" build a few rocket mass heaters with very short chimneys, and others with a horizontal exhaust pointing downwind. But this does not mean that "you can" count on this party-trick design working adequately in your actual situation.
So "you can" build with metal, and "you can" call a rocket mass heater a rocket stove.
But we would very much prefer if you didn't call random metal stove experiments a "rocket mass heater," especially if it is based on unproven ideas, or on some other non-mass-heating prototype which has never proven itself over a full heating season.
I still like Paul's term for new experiments in this field: "Freak Show of Flaming Death."
I have made some of my living these past 10 years by entertaining crowds with dare-devil fire tricks and my husband's hard-won ability to handle hot objects with his bear
hands (pun intended, he has caluses that frustrate carpenter ants
So we do resemble this remark.
Good judgement comes from experience, and a lot of that [experience] comes from bad judgement.*
Ernie and I have put in a lot of experience-time prototyping with metal, replacing crapped-out metal, repairing masonry damaged by crapped-out metal, troubleshooting a chimney fire due in part to crapped-out metal, and inspecting other people's labor-intensive metal prototypes (which generally crapped out within one season of use, or were discarded before then).
The charts' predictions about the type and temperature of metal failure seem to correspond with our experience. We have had some embarrassing repeat visits to clients whose stoves needed repair due to our early optimism about high-grade metal parts.
We have also seen other kinds of failure from metal/masonry hybrids, due to incompatible thermal expansion differences between most kinds of metal and most kinds of masonry.
So if you care to take the benefit of our experience, you may save yourself some trouble.
If you LOVE working with metal and want to help solve these problems in a productive way, I have a LOT of project
ideas for pairing high-quality metalwork OUTSIDE the firebox with high-quality refractory materials inside.
Thanks for reading.
*'experience' quote sometimes attributed to Will Rogers; I think another version was penned by Mark Twain.