old wood cook stove modification

I have one of those old stoves that have removable covers on the cooking surface and an oven and warmers on top each side of the flue pipe (it is a big one.)

I was wondering if their has been any one trying to convert the fire box to a rocket type burner.
The fire box on mine has a door for the wood and below it a door for the ash clean out.

Thing is their is a lot of thermal mass to heat up in these old stoves.

Just a thought.................

woodman wrote:
I have one of those old stoves that have removable covers on the cooking surface and an oven and warmers on top each side of the flue pipe (it is a big one.)

I was wondering if their has been any one trying to convert the fire box to a rocket type burner.
The fire box on mine has a door for the wood and below it a door for the ash clean out.

Thing is their is a lot of thermal mass to heat up in these old stoves.

Just a thought.................

There's certainly been a number of people interested (including me), but most of us don't happen to have an old woodstove handy to experiment with.

Have you seen the designs for a Pocket Rocket?
It's built with scrap metal (a bucket or barrel, and 2-3 pieces of stovepipe in various sizes).  Air and wood feed downwards through a narrow gap near the bottom of the feed tube; and the fire burns all different directions for good mixing and complete burn.

I think you might be able to do the same thing with a woodstove.  Especially if you can take the round lid right off the front burner, and convert that to a wood feed.  Maybe put some firebrick or tile under the feed tube, to convert your ash grate to something more like the baffle / floor of a barrel.

If you try it, I'd love to see how it goes.

Yours,
Erica

I think there's a pocket rocket in our Fire Science slideshow, but it doesn't necessarily show how they're made:
http://picasaweb.google.com/eritter

I have the same type question. Is there more about converting woodstoves into Rocket Heaters. I want the efficiency (or near the efficiency) of the RMH with the quick radiation heat of my cast iron stove, to be used as a sauna.

Jason Munzke wrote:I have the same type question. Is there more about converting woodstoves into Rocket Heaters. I want the efficiency (or near the efficiency) of the RMH with the quick radiation heat of my cast iron stove, to be used as a sauna.

You can build a RMH without the mass ( a rocket air heater) by adding lots of surface area for heat exchange after the heat riser (like extra barrels). I have converted woodstoves to rockets by adding insulated heat risers and have this problem of looking at every woodstove I see and imagining how I'd rocketfy it. There have been alot of fun ideas but I much prefer to build rockets from firebrick as it is generally much less work and lasts longer and I believe more efficient. Canyon

So if I understand, you would use large barrels for mass and put a few in succession before running into mass or out the chimney?

Jason Kootenai wrote:So if I understand, you would use large barrels for mass and put a few in succession before running into mass or out the chimney?

If yer building a rocket stove as a sauna heater, you should know that mass is just about useless. Mass takes time to heat up and also to give back, which is EXACTLY what you want for heating a home but exactly wrong for saunas.
Saunas need a stove that will dump it's heat directly into the space, also, the sauna itself should be built out of light, insulative materials. Cob saunas tend not to work very well, all that mass saps heat away and gives it back too late(unless you plan to camp in the sauna, then it'll be a better hut than sauna).

So. An extra barrel in the flow path is a great idea, treat the second barrel as a "bell", that is, the intake (from barrel #1) and the outflow (to chimney) should be at the bottom (floor level). The intake should be a little bit higher to separate the flows from each other (yes, the intake to the barrel should be higher than the outflow) Heat will enter the barrel and fraction, or separate, hottest stuff at the top, coolest at the bottom and out. This will insure that MOST of your heat is radiated into the sauna very quickly. Don't bother with mass storage, when the exhaust leaves the second barrel, just pipe it outside through a chimney.

If you would rather not fool with double barrels (though it will work better that way), a simpler way to go is to over-gap the regular barrel. Raise the barrel much higher than usual and provide as large a gap 'round the sides as is practical. This will make the gasses hang out for longer in there and allow more time for heat exchange. With a higher barrel, the part above the heat riser will act like a bell (described above). How much to raise the barrel is up to you, just gotta figure how much space you have and what the practical implications are, etc.
As always, test it before you rely on it.. If you've never built a rocket stove, build it outside FIRST, get it right, then move it inside.

Great information, thanks. I am going to play with a pocket rocket type of design. I have a old Sears and Roebuck "cigar type" wood stove with two removable burner lids and a chimney vent. The first lid will be the intake wood feed. The second hole will be the Rocket with a barrel over top for the gasses. I haven't yet figured out what I will do to vent the rocket gasses out to the chimney pipe; also I am not sure if the 3rd hole (the actual chimney) will actually aid in the "rocket-ness" of the stove or will it draw too much of the gas out of the firebox and not allow the rocket to work to full potential. I suppose I could use fire bricks to impede the premature exhausting out of the chimney (Ahh, I need to draw a picture). If anyone knows what I am describing and has input, please comment.

Well, it seems to me that converting an old stove to act like a rocket stove is more hassle than just building one from scratch..
Having said that, it's been done before, from what I understand, to good effect.

Jason,

It might help to abandon the heat riser. You don't absolutely need it because you will be venting your flue gases directly out the chimney. The internal heat riser in the RMH is not what makes it a rocket stove.

A rocket stove is, IIRC, an insulated (though not always insulated) duct or flue of relatively constant internal cross-sectional area, in the shape of an L or J (though not restricted to those shapes). The constant cross-sectional area keeps the gases moving. The insulation helps to keep the flue gases from cooling before combustion is complete and maintains draft. (Those are the rockety parts)

In an RMH, the internal heat riser, made by putting a barrel over a J-shaped rocket stove, is used to help passively pump hot flue gas through the labyrinth of ductwork.

I have been brainstorming some options to convert a conventional wood fired cooking stove to a rocket configuration and I think that a simple retrofit could use Alex English's wood chip/pellet burner design (refs: 1, 2, 3, 4), but modified to use stick wood. It would look something like the fuel feed and combustion chamber in Len Oven's Portable RMH.

In the L or J shape, the long leg is ALWAYS the heat riser.
If it's gonna be a "rocket stove" it's gotta have a heat riser.
Other arrangements may work just fine, just won't be one 'o them.

By the way, IMHO, pocket rockets AIN'T "rocket stoves".

Kirk,

Great, a nomenclature discussion. The chimney or flue of the rocket stove in the RMH is referred to as a heat riser to distinguish it from a chimney because it does not directly exhaust flue gases. One could refer to it as an internal chimney, but it appears that the preferred nomenclature on this forum is "heat riser". Conventional nomenclature would be more appropriate when using a rocket stove in other configurations because referring to the chimney as a heat riser seems to include a fixation on the RMH's heat exchange barrel.

The description of the rocket stove could be simplified to an elongated, insulated combustion chamber of constant cross-sectional area. The chimney may be the combustion chamber or placed several steps down the system.

At a point, a design evolved from the rocket stove becomes different enough to have its own label.

I agree that a pocket rocket is not a rocket stove, but it is a simple, interesting design.

Andrew Parker wrote:Jason,
The internal heat riser in the RMH is not what makes it a rocket stove.

A rocket stove is, IIRC, an insulated (though not always insulated) duct or flue of relatively constant internal cross-sectional area, in the shape of an L or J (though not restricted to those shapes). The constant cross-sectional area keeps the gases moving. The insulation helps to keep the flue gases from cooling before combustion is complete and maintains draft. (Those are the rockety parts)

In an RMH, the internal heat riser, made by putting a barrel over a J-shaped rocket stove, is used to help passively pump hot flue gas through the labyrinth of ductwork.

Hi Andrew,
I am not sure if you really want to have a nomenclature discussion (I am frequently challenged discerning when people are serious or sarcastic) but I am interested in clarification of these terms as I teach people this stuff and would like to be accurate. I have been teaching that the main defining feature of a rocket is the insulated "heat riser" or "internal chimney". The internal heat riser is made by insulating the internal VERTICAL chimney (which the L or J shapes inherently have), not by putting a barrel over it as that is just one option for heat exchange or flue gas path. I like your effort to simplify the rocket stove definition but I would say that it could be simplified further by dropping the words "chamber of constant cross-sectional area" and adding the word vertical. So the description of a rocket stove could be simplified to an elongated, insulated combustion chamber with a vertical leg. An evolved design without that vertical insulated heat riser would indeed be at the point of difference to warrant its own label and NOT be considered a rocket. Feedback?
Canyon

Andrew Parker wrote:The description of the rocket stove could be simplified to an elongated, insulated combustion chamber of constant cross-sectional area. The chimney may be the combustion chamber or placed several steps down the system.

I've been at the rocket stove thing for a while, I teach 'em too... So far, every definition I'm aware of includes the "heat riser", insulated chimney, whether internal (RMH)` or external (Aprovecho-style cooker).
I am open minded (like to think so) and am curious about your definition. Could you detail out the repercussions of your thought-form? What would a rocket stove without a heat riser look like? What would it share with other "rocket stoves" and what would it not?

Lasse,

Regarding the nomenclature discussion of 'heat riser' v. 'chimney', I will stand by my previous statements. I have only encountered the term 'heat riser' in discussions of the RMH. For those who came upon the rocket stove through the RMH, it appears that the term 'heat riser' puts an image of the RMH's barrel into their brains. Referring to a rocket stove's chimney as a chimney might unburden them of that. I have little argument with the use of 'heat riser' in the context of the RMH or any other design in which the rocket stove's chimney is used to push flue gas in directions other than up, though 'internal chimney' might be less confusing for the uninitiated.

Kirk,

The J configuration is a good start in attempting to explain what I mean. Combustion begins at the bottom of the short vertical feed tube, travels horizontally to the chimney (heat riser), then up, petering out somewhere in the chimney. If you were to lay the chimney down to make one insulated, horizontal combustion chamber/flue of constant cross-sectional area and of a length sufficient to complete combustion, then apply draft supplied by a chimney somewhere further down the system, I think you could still legitimately call it a rocket stove, however, I agree that by then it may have evolved into something else.

The J configuration is a good start in attempting to explain what I mean. Combustion begins at the bottom of the short vertical feed tube, travels horizontally to the chimney (heat riser), then up, petering out somewhere in the chimney. If you were to lay the chimney down to make one insulated, horizontal combustion chamber/flue of constant cross-sectional area and of a length sufficient to complete combustion, then apply draft supplied by a chimney somewhere further down the system, I think you could still legitimately call it a rocket stove, however, I agree that by then it may have evolved into something else.

Ok.. I think I get the point.
The term "heat riser" is used to delineate the internal chimney from the external one.. Early on, when trying to describe RMH's, there was some confusion. So the new term was coined (I mean c'mon, what IS a chimney but a "heat riser"?) so that you only needed to say, "short, hot, internal chimney" once in the conversation and from there on, everyone knew what you were talking about. I've heard it referred to as a "heat siphon" as well, possibly for similar reasons.
As to the constant area thing: Once again, the rule was made to keep it simple for the noobs. It was written in the book that way 'cause the model had to be simple, easy to build and work all of the time with minimal alteration. Same with the barrel, the lengths and dimensions, etc, etc. We're trying to spread the technology without a lot of confusing, screwy results. There's ALREADY enough confusion about them as it is, best to keep it simple.

The truth is that when air changes temperature, it changes volume as well and there are improvements that use this to advantage. There are shape and volume changes that can (and do) GREATLY improve RMH performance. Most of these alterations are still experimental but are showing great promise. I expect that before long, there will be a lot of RMH's out there without constant cross sectional area, though I also expect that they will ALL still posses a "heat riser" of some kind.

I know what you mean about simplicity. I was going to expound about Reynolds numbers, etc., but realized that the rocket stove manuals are wise in simply instructing people to maintain a constant cross-sectional area. There were some very good, and very, very expensive, proprietary programs 15 years ago that could calculate Reynolds numbers on the fly while designing a system of pipes and/or ducts (I didn't use them. There were CFD scientists in my working group who did. I am not a scientist or engineer, but I worked with them.). There are probably less expensive apps for that now.

Iirc, there was some discussion on the stoves list about the pot and skirt gaps in rocket cooking stoves being adjusted for temperature.

'Thermal siphon' or 'heat siphon' could encompass the internal chimney (heat riser), barrel(bell?) heat exchanger and condensing heat exchanger, but, 'thermal siphon' is popularly used in solar heating systems and 'heat siphon' is a registered trademark for a pool heater in the US so there may be some confusion.

Aren't nomenclature discussions fun, even if sometimes useless? I have learned all kinds of things while researching my posts and responses.

Yeah.. Nomenclature discussions are often frustrating and fruitless..
Words are powerful though, they form pictures in our mind(s), create models that we can act on.
It's why I so often get into the stupid nomenclature struggle.. I wan't to paint the right pictures, which can lead in useful directions. So often, I find that the words that we hang on things paint screwy, inaccurate pictures, which lead to unnecessary mistakes.

One of my favorites: "heat rises", which is technically incorrect, though experientially it seems right.. I almost always knock this one down immediately during a rocket stove class, it's an assumption that can lead to poor design, etc. etc. Heated fluids will change density and rise, true, but that's a property of fluids, not heat. Heat travels in straight lines, equally in all directions, depending on the medium that it travels through.. Yadda, yadda and etc..
I'm sure you can see where this is leading. The point being that when designing a system that pumps heated fluids (air) DOWN and horizontally, you've got to have a useful image or you're likely gonna flub it.
Anyway, enough of that.

Anonymous wrote:I have one of those old stoves that have removable covers on the cooking surface and an oven and warmers on top each side of the flue pipe (it is a big one.)
I was wondering if their has been any one trying to convert the fire box to a rocket type burner.
The fire box on mine has a door for the wood and below it a door for the ash clean out.
Thing is their is a lot of thermal mass to heat up in these old stoves.
Just a thought.................

Rocket stoves, generally have two, and arguably three defining features:

Rocket effect (super flue)

Thermal mass (mass heater)

and a convenient fuel mechanism (the "feed")

With an antique Wood fired cook stove you have the Thermal mass covered, and the addition of fuel is pretty darn convenient already with a nice shaker box for ashes and the like with air controls and the like, we can ignore those for this application.

What a wood cook stove does NOT have is the rocket-effect, that oh so satisfying "woosh" of the super flue phenomina<sp?>.

Since you really can't, duct the wood gasses arround a wood cook stove too much without defeating the idea of a "cook" stove you're stuck with modifictions on flue as it exists the stove on its way to the ceiling.

An aggrivating issue is going to be the internal air resistance of the stove, there are a lot of ducts and inconvenient right angles and the like that make what I'm about to suggest iffy on whether it'll work, basically, will the enhanced flue phenomenae initiated by the modification be sufficient to overcome the inherent resitance of the stove Y/N? As each antique stove is different you're going to have to play arround to see, no garuntees sorry.

First off, make sure the stove is REALLY clean(Spotless inside and out!) and has new fibreglass bushings everywhere. You might also think about replacing the firebrick/soapstone with some modern nifty material which is better; my experience is in smelting so I'm NOT going to go suggesting what I'm familiar with, again, experiment, if you start melting the steel of the stove I think you need to dial it back a bit (YES that can happen with enough BTU!).

Next, you can't change the stove but extra fire brick is a variation to play arround with (Adding thickness), it reduces fuel volume but if this works you're not going to need it.

To get the superflue effect you want:
1. A really hot fire (extra fire brick will help that but watch the oxidation state on the top of the stove, if you start seeing rainbows it's WAY too hot!).

-- Here's the meat --
2. A modified flue to ceiling which gets a little complicated. Most small rocket stoves get super flue effect either by super high temperatures alone (You hear stories about guys getting a "good flue" by running their stoves for days on good fuel in a regular stove, let alone a rocket stove.) or by some giant barell on the flue which increases the available surface area before the smoke is vented. If you have a warming cabinet you loose from the top of the back splash to the top of the warming cabinet in terms of square feet of radiative cooling space, this may or may not make it impossible to pull off, it depends on how you implement it. Basically you make a big metal box on the back of your stove (With lots of clean outs, this'll turn a nightmare cleaning job into one thats merely odeous.) that runs upto a few feet off the celing with the output of the stove entering in at the bottom and a standard stove pipe inserted into it like a straw in a can of pop that heads for the chimney. Getting clean-outs for the box and that straw flue is tricky and I leave that to your imagination, there are all kinds of ways of doing it and it'll depend mostly on how flexible you think you're going to be when you're cleaning it. Remember hot air rises and have the flue from the back of the stove release it's gasses as high in that box as possible and the original stove pipe / straw should start as low as possible, in a perfect world the place where the straw/old stove pipe exits for the chimney gets a little blow of hot gas directly from the stove to encourage things to move in the right direction (straw draft improvement.).
-- There's the meat --

Trick is making it look nice and not like some neo-industrial-impressionist art on one end or something Red-Green would be proud of and using loads of duct-tape. Wood-cook-stove rocket converting flues would be a nice side line someone might look into, there's money in it.

Heck, the extra soap stone might be enough but you're going to have to experiment, do a good job, be proud of it, document it on youtube with all kinds of nifty guages like flow meters and laser thermometers or better yet an infrared scope and you'll be the next YouTube sensation...if you can get past the filter wall of all those dang propane/electric wood-cook-stove converstions.

Good luck!

ps. my system just crashed and I have no functional spell'n'check so please ignore they spelling erros.

Trick is making it look nice and not like some neo-industrial-impressionist art on one end or something Red-Green would be proud of and using loads of duct-tape. Wood-cook-stove rocket converting flues would be a nice side line someone might look into, there's money in it.
Heck, the extra soap stone might be enough but you're going to have to experiment, do a good job, be proud of it, document it on youtube with all kinds of nifty gauges like flow meters and laser thermometers or better yet an infrared scope and you'll be the next YouTube sensation...if you can get past the filter wall of all those dang propane/electric wood-cook-stove conversions.

Quick follow up: Remember that the cooler your exhaust the more likely you are to build up creosote , I thought I should mention it, ergo, you're clean up needs are going to be higher than one of these rocket stoves that get up to thousands of degrees and vent out under a wok or some such.

Some pre-fab and quick-fixes I found are at the following links:

1. Lehman's - Baker's Salute Oven {Pretty much covers the needed surface area; however, needs to be mounted 12" from stove top which unless you have a BIG kitchen, might not be possible. } https://www.lehmans.com/p-4873-baker-s-salute-oven.aspx


2. Tjernlund Chimney Fan {Quick Fix: Fast way to induce lots of draft and has workable chimney cleaning feature. Oh yes, expect sticker shock!} http://www.youtube.com/watch?v=hjeEoBMQhMQ&feature=share&list=UUea8G6A83FNAJn5I8MauocQ


3. Turbocamino chimney fan {Quick Fix: Fast way to induce lots of draft, not sure about ease of cleaning, reasonable price.} http://www.hellotrade.com/o-erre-spa/centrifugal-fan-turbocamino.html

Again, good luck!

Agree with you.  In fall and late spring I take the firebrick out of my stove and save a bunch of firewood not heating up the bricks and get quicker heat.  Firebricks are meant to cause a hotter fire to have less emissions and not necessarily for getting a room heated quickly which is all that is needed during chilly times as opposed to days on end at near or below zero like it can get here in Maine. It has not hurt my stove with no firebricks and ashes protect the bottom of the stove. A woodboiler used like a battery charger with a large water storage tank as the battery is the best set up I have had. The fire can burn at a good efficient high rate with little or no smoke and your house gets steady heat like a normal boiler. The fire is almost separate from the heat load...no more getting roasted out and opening windows and doors or smoldering a fire in an "all nighter air tight stove".

Removing the bricks? I dunno, maybe in a cheap stove with a sacrificial sheet metal liner and very small stick fires. Otherwise IMO there's a risk of overheating and warping the stove.

My understanding is that any stove with a UL type listing would be engineered and tested with the bricks as part of the system. Aside from physical damage to the stove, the clearance to flammables may also be affected (increased).

If nothing else, I think it would give your insurance company a golden opportunity to deny a claim. So watch your back. My 2c.

Addressing the op's question, a lot has developed in the intervening years.  A possibly less complicated adaptation for the existing combustion chamber could be some form of batch box configuration (check out Walker Stoves' riserless solution, and there are many other options).

As to removing fire bricks for quicker room heating, someone skilled in the art could build a relatively efficient fire in an unlined metal stove without risk of damaging the metal.  For everyone else, maybe best to keep the brick lining and look into inserting better heat exchange outside the stove.

The general goal of these new unconventional designs has been to separate the combustion area from the heat exchange.  Maximizing combustion efficiency eliminates most, often all, the traditional problems with cooking and heating with biomass and coal (naturally aged, carbonized and compressed biomass).  Maximizing efficiency of heat exchange for cooking or heating allows a significant reduction in need for fuel (and emissions).  This separation of tasks greatly simplifies designing maximum efficiency of each.

In approaching the modification of a "conventional" stove, heat or cooking, it will be simpler to first determine what the stove body will better perform as:  combustion chamber or heat exchanger.  The op's cooking stove had an integral combustion chamber that needed improvement.  Modification of the integral combustion chamber could have worked, but there were external options as well.  Most heating stoves are best modified to be better combustion chambers, then add an efficient heat exchanger somewhere along the flue.

To throw a bit more confusion into the discussion of what a rocket stove is or isn't, I cite the rocket tobacco drying barn designs of Peter Scott where he uses an entirely horizontal, inline feed and combustion chamber tube that sends hot flue gasses through horizontal floor heat exchangers before being vented through a vertical insulated chimney.  Whatever works.