Friday, November 11, 2011

About This Site

This site describes a subset of biomass cooking stoves for developing countries, and is intended as a resource for those working in the field. It tries to organize key existing online materials, as well as highlight new contributions that will hopefully be stimulated by a continuing discussion of new designs and approaches that seek to focus on developing open design ideas that can be deployed in any country, quickly. To comment or submit email Charlie Sellers (Berkeley, CA) at

Other resources that may be of interest include my more general technical sites:

and the always more extensive "master site" of stovers worldwide called Biomass Cooking Stoves:

The dates on these posts are presently bogus, just because I wanted a site where the newest posts are last - so that all the intro material is initially up front; this may change in the future.

Friday, January 1, 2010

Urban Justa Building Workshop in San Francisco

July 25th somehow I just barely found out about a Justa IAP stove building workshop in my own area - Sebastián Africano and Honduriano ace stove welder Marvin stumbled into my shop in Berkeley and spent one day making a sheet metal oven and two days assembling/teaching in a beautiful permaculture yard in the Sunset district. Though we have never met, Sebastián and I have practically known each other for years based on the number of contacts we have in common (ADESEA/TWP in Tegucigalpa, ClimateCare/JPMorgan, Aprovecho, AbientalPV in Brazil, etc.) and it was a great opportunity for me to get dirty with these two compadres from ENASA.

This was to be a jumbo Mercedes/Cadillac of stoves, combining aspects of several different models - a metal bread oven like the ADESEA/TWP metal stove design (EcoFogon), an extra large plancha, a metal clean out port and place for gas to swirl on the way to the 4" (10 cm) chimney, a 4.5" (11.5 cm) diameter brick tube Rocket combustion chamber, and of course mostly found materials. I had just this week been struggling with my own steel plancha experiments - too thin and they will warp badly in intense flame, too thick and and they cost too much money to buy (a .63 cm plancha may weight 25 lbs!) - and will try their design of 1/8" (.32 cm) thick, with 1" (2.5 cm) square tubing frame around the perimeter and a sacrificial plate right over the firebox. This is set into a bombproof poured concrete retainer so that it locates perfectly and the sides are sealed from unwanted air intrusion.

First the initial flight of bricks is laid out, taking into account the dimensions of fixed parts like the oven, plancha, and cleanout port (the concrete platform had been poured in two layers the day/night before). The can and 45 degree cut brick tube were secured on top with shaped brick pieces (we would be chiseling many of the bricks to fit) and then we built up the rest of the brick layers - lots of hands involved at once - keeping everything straight and level. A hollow cavity at the rear was bricked over and a chimney support structure was built on top, keeping all openings in the gas flow path equal in area to the fuel entrance one.

The hand sawn (with a tungsten carbide hacksaw blade) 45 degree bevel on the combustion chamber did not match perfectly so the elbow had to be supported well and mudded in, then the area around it could be filled with volcanic perlite for insulation - Sebastián and I vowed to develop an alternative to just this and wood ash for a cheap quality filler material. The next day a perimeter concrete slab was poured across the top for the plancha to seat into, thick enough so that it wouldn't crumble over time - the adjustable flap behind the combustion chamber either steers the hot gas down around the oven or lets it flow the full length of the plancha. We used the stove just after building it, monitoring the oven and chimney temperatures to check initial performance - it was still a little wet but it heated up great with minimal wood or attention. We discussed that if a cook is not thrilled by the stove the first day, within 3 days she will have warmed to the change and be happy with its operation and performance - and it can be helpful to stop by, cook, and provide encouragement during this time period. User modified stoves are always a possibility, can defeat the purposes and advantages of the stoves, so should be prevented by any combination of hooks and crooks.

This was a great communal build, with nice weather and a great crowd - and what a beautiful stove they'll have to cook on and demo for the neighborhood - stoves in urban areas like this help raise awareness for clean and fuel efficient stoves to be built south of our border. I don't know if this urban backyard Justa barbeque building party will take off in developed countries, but it is a great educational tool. And in contrast to many more technical stover events we actually cooked a multi course meal - fresh vegetables, a rice dish, and 2 batches of cookies - ¡Qué rico!

Here are some links to Justa building:
another from Aprovecho, in Spanish, a video about the Justa in Honduras, and a detailed Justa efficiency testing article

Sunday, December 27, 2009

Components of an IAP Stove

It is helpful to provide names for the parts of a typical IAP stove (which tends to be a subset of rocket stoves - see post on these below for an overview):

  • Outer walls ("the box", or similar) - the enclosure that confines the smoke and sends it up the chimney, and it provides a low temperature exterior for safety. Easiest to make from very local materials.
  • Combustion chamber (or firebox) - constrains the fire so that it is as hot as possible (to burn the smoke), should be inexpensive/high temperature material/low thermal mass; very often it is the "rocket elbow" and is formed by the intersection of the horizontal wood entrance arm and the vertical Rocket/combustion chamber chimney.
  • Rocket chimney - the vertical passage above the combustion chamber, for the fire to heat the plancha after the smoke is burned
  • Fuel entrance - the part of the rocket elbow that the cook feeds the wood in, after it is pre-heated while being introduced to the fire slowly; the air entering the fire is pre-heated as well
  • Grate - it supports the wood inside the wood entrance, so that air can flow in below the fire, and it keeps the wood and charcoal embers up and out of the ashed
  • Insulation material - a low thermal mass (porous) loose material that prevents the heat from the fire from traveling far - wasting heat that could be used for cooking food. Typically wood ash or a volcanic material like pumice.
  • Plancha - the metal (usually) plate upon which the food is cooked, either by intimate contact (dead animal parts, breads, etc.) or inside of pots. Very often there are adjustable pot holes so that the fire can directly contact the bottom of the pots (note that the pot can either be on the surface or allowed to drop below the level of the plancha - hopefully improving heat transfer sufficiently to warrant the extra cost. Inkawasi stoves may not have a plancha, replacing it with a ceramic surface that has pot holes which the pots fit into (dropping their bottoms below the surface so that they are in the flames).
  • Flame space - the area underneath the plancha where the flames coming out of the combustion chamber chimney flow under the plancha
  • Filler space and material - some of the area under the back of the plancha, where scrap materials can be placed to avoid using too much insulative material (since it should not absorb too much heat).
  • Chimney - which carries the smoke out of the kitchen/house, connecting to the flame space. Should be witha long lasting (can't corrode easily) and earthquake resistant material and design.
Somewhat in order of importance for engineering design purposes:
  • Combustion chamber (plus fuel entrance and combustion chamber chimney) - the whole "rocket elbow" was postulated/developed by Dr. Larry Winiarski at Aprovecho, and is usually made as a single assembly out of the same material necessarily a high temperature one since it comes in direct contact with flame. It is possible to make this whole elbow in one piece (usually crafted by a potter, out of clay) but it tends to be made in 2 parts (fuel entrance and chimney, with the combustion chamber being the intersection of these), and sometimes more. The material is the most important aspect, since at very high temperatures (perhaps up to 1100 oC) most materials are susceptible to degradation and breakage. Previous materials for this part have included mild steel, stainless steel, cast iron, and all types of ceramics (mud, bricks of any kind). Metal, besides cast iron, degrades relatively rapidly and are also expensive, cast iron when too thick requires too much time to heat up, and soft bricks have the potential to be damaged too easily. Hardness and other mechanical properties (including resistance to cracking), thermal characteristics, and cost are of primary concern but also to be considered is the ease of construction and stability over time. More recently, low thermal mass ceramics have been preferred by some so that the majority of the heat flow is limited (and doesn't spread to unwanted places) and thus is more concentrated in the firebox - sometimes proposed is the use of these in a combustion chamber made from several custom "bricks". The six brick architecture is usually used for a complete stove, but placing it inside an IAP stove should not seem unusual - it can be made very locally and inexpensively. This would replace the typical, often fragile/brittle, "baldosa" tile material (as is used in stoves such as the ONIL, in Guatemala). In any cases the materials must either be cut from flat tiles or cast/formed into the appropriate shape before firing (see here for an Aprovecho insulative variety, but the proper plain clay bricks should be sufficient since there is insulation around the combustion chambers in IAP stoves) - it may be that a four brick approach is almost as stable and takes slightly less expertise to make reliably.
  • Plancha - the plancha is typically made from 1/8 " - 1/4" thick mild steel - cheap and readily available in developing countries (cast iron ones are best for corrosion resistance but are more typically used only for restaurant-sized versions). The two primary types are the plain flat plate and ones containing adjustable pot holes (plasma torch cut?) - while the pot hole version may be preferred, the flat plate one is much cheaper (since it takes no specialized equipment, and is more commonly available). In either case the durability and structural integrity is important - too thin and it can warp to to thermal stresses, so often it is often reinforced on the underside, adding cost. Also, an additional metal plate may be welded to the underside, immediately above the combustion chamber chimney, since this has the most exposure to very high temperatures and so is more susceptible to early failure. If too thick the plancha can cost too much (though it will be less prone to warping) - metal is sold essentially by the kilogram) so 3/16" is more common than 1/4" since the later is 30% more expensive. Planchas can be made either from new metal (from a ferreteria or local metal supplier) or recycled metal (from a blacksmith), with the latter preferred for flat plate planchas. All planchas must be maintained regularly by the owner - the top scrubbed with a stone to remove rust, and the bottom cleaned to remove carbon build up. I am just checking now on the price of potential plancha materials in the U.S. - new metal with dimensions of 14"x28"x3/16" (ONIL dimensions) from McMaster Carr, as an example of cost vs. thickness and area.
  • Outer walls -I have typically made the walls from hollow bricks, assuming that the most important characteristic is cost per unit volume, but now I see that the insulating material around the combustion chamber (usually +5 cm all around it) is sufficient for keeping the outsides of the stove cool. Filling hollow bricks with insulating material is noble, but if it is not necessary it consumes too much valuable material (e.g wood ash is hard to get in quantity, and the interior volume of these bricks can be as much as the inside of the stove) - as long as there is sufficient insulation inside the walls they may not need to be filled except at the top adjacent to the flame space, so the wall thickness can be reduced and the overall width of the stove reduced. The ONIL stove uses concrete for the walls, and the TWP stove (and others) use a sheet steel skin to contain the insulative filler - as long as there is sufficient insulation around the combustion chamber, and the material in contact with the flame is resistant to degradation by the flame, almost any material can be considered. In the past, rammed earth was used, but this had a high thermal mass when it was not combined with a porous insulative fill material on the inside. Now, ordinary bricks, and even stone, can be used, as long as the combustion chamber is properly insulated.
  • Insulation - This material, usually "loose" (free flowing - not a super fine powder, but granular) is preferably low thermal mass (e.g. filled with air spaces) - wood ash, pumice, vermiculite, perlite, and crushed porous brick are usual materials. Many people think that sand or stones are appropriate, but these are high thermal mass materials which tend to absorb lots of heat from the combustion chamber, preventing a hot fire from developing quickly (which is necessary to burn the smoke). Loose materials tend to be used because they fill small spaces easily, but high temperature fiberglass may be an alternative (or aerogels and simililar high tech materials with lots of air space inside). The local availability of this material is an importyant consideration - contries with volcanoes tend to have easy access to pumice, while wood ash can be more common (but hard to get in quantities need for mass production of stoves. In any case, minimizing the amount of these insulative materials is helpful - it should only be used very close to the combustion chamber and places in contact with flame (high temperatures) and other places where other materials are inappropriate.
  • Chimney - this part removes the smoke from the kitchen, and like all components it should be low cost, made from local materials, have good durability and mechanical strength (including earthquake resistance), and be easily maintained (cleanability). Metal tubes are the most common chimneys, but they tend to degrade via corrosion at the bottom and perhaps only last one year; chimneys made from hollow bricks are very cheap and durable (and can be made earthquake proof with steel reinforcing) but cannot easily be cleaned. Mud and stone chimneys are the least expensive to build, using only very local materials, but are not commonly used.
  • Filler material - this component is perhaps the least important, since it is far from the combustion chamber so has little possibility of stealing heat which could be used to cook food. Located toward the back of the stove, the materials can be things such as broken bricks and other rubble, stones etc. - anything to reduce the amount of insulating material used.
Materials and Design Recommendations - and Problem Areas
After all this discussion about the various components, how should each component be made - what guidelines should be followed? The general principles of local, inexpensive, simple, and maintainable should be our guiding principles - what is available locally is the first thing to consider, so exploring the neighborhood is the first order of business. Blacksmith shops, construction material suppliers, home repair stores, hardware stores, brick yards, etc. all have to be checked to see what the full range of materials is available for each and every component( i.e. don't arrive at the site with pre-conceived notions of an exact design, set of materials, or cost). Metal plate for the plancha can be tricky, as well as materials for chimneys - these may be the most local-dependent. If planchas without pot holes are not commercially available (or are too expensive (often $USD 30), then don't plan on these, and the same for metal chimneys!

Tricky parts of a non-cast cement mono-wall (like the ONIL - at this point this design seems too expensive) are these few stove areas:
  • the part of the front of the stove wall (facing the user and above the fuel entrance) where you must sometimes have an insulating brick material, if it touches the combustion chamber
  • the combustion chamber material and design - even if we have good flat materials (like baldosa tile), how can be make the chamber and fuel tunnel so that it can be made, fabricated, and perhaps shipped (from the brick kiln) easily? Of course it must be high temperature resistant, when nothing else in the region may need to be. If this part fails, then we have lost the battle.
  • the connection between the fuel tunnel and the combustion chamber - should be tight so that it is mechanically strong, and so that air does not leak in (particularly in the case of a cylindrical combustion chamber).
  • the thin joint between the plancha and the chimney, to keep air from entering the stove (the same is true everywhere around the plancha - smoke will not blow out, but unwanted cold air can enter).
  • the joint between the chimney and the stove body can be a weak point if not designed properly (supporting the chimney, since it has a hole in it to remove the smoke from the flame space it, can be weak point).
  • the chimney - popular sheet metal chimneys can corrode in the bottom segment as soon as in one year (users may not replace them, defeting the purpose of the stove) so a better design is needed. There is little experience with rock/mud/adobe/block chimneys it seems, or a combination of these materials. And how can the chimney be supported, if there is no house wall or strong roof?

Thursday, December 11, 2008

Implementing IAP Stoves - Working With Communities

I have long thought that a stove project is more that technological improvements - the parts that engineers typically are involved with. I started with thinking that the technical part (stove experiments and drawings and such) was 50% of an implementation, then I changed to 30%, then 10%, then Mark Jacobs convinced me (at ETHOS 2008) that 2% was closer to reality. Hence 98% of the success of a new stove project is due to non-technical, on-the-ground teaching. cooking demonstration, marketing, sociocultural, anthropological. hands-on, get dirty activities! So much for us scientists/engineers.

What can we do about this - remove the scientists and engineers from the project, or figure out how the social scientists can help? I am not the first to realize this, but I am certainly a minority within the stover community. A good place to start our analysis is with our usual stover master site, at the dissemination tab:
where the results of many projects are discussed. A worst VERY recent case set of scenarios is here:
where all/most of the stoves deployed in Ugandan refugee camps performed worse than primitive three stone fires - perhaps because not enough time was spent on education (as to how these stoves should be used)? All of us should read this discouraging article!
Another thing we should read is this one on intercultural engineering - working within local constraints:

A very simple list of activities and documents that might be included with the technological information, when a stove project is implemented, might be:

  • what do we need to know about the present situation? - stoves, fuel collection activities (and responsibilities), financial decision making roles, etc. Always, questionnaires are needed, and lots of time for observations and over-the-stove discussions.
  • a clear description of why "improved stoves' are needed - what is "less optimal" (not "wrong") with the present situation, what benefits new stoves offer, and what changes (e.g. in cooking practices.) may be needed.
  • how will stoves be constructed - materials, labor. and costs...? Who will construct them and what will these people need to know (in the form of posters and such) to do it as well as is possible?
  • what stove operation teaching information is required - posters. handouts, competitions, cooking classes. etc.
  • what "marketing" techniques will work best within this particular community? - guerrilla and viral marketing methods should be investigated - shock and awe, sneeky, selective free give-a-ways, lotteries, competitions. demos, etc.
  • how do we determine if the stove implementation is successful and can be improved?

Saturday, January 19, 2008

What is "Indoor Air Pollution"?

As is usually the case, I defer to experts and other authors to provide existing information to you the reader - I did not identify IAP as a problem, I have not invented any new IAP stoves, and so I am mostly here to consolidate key information, disseminate old data that is already on the web, and when I can I contribute the results of my own experiments and experiences. Basically, my own interpretation of IAP as it applies to cooking/heating stoves in developing countries can be found in the resources list below (a select few of all that are out there and easily available). For your reference, it is easy to search on indoor air pollution topics on the internet - luckily if you use Google "IAP + stoves" it leads you to a very narrow field;

The World Health Organization (WHO) has a good introduction here:
and next you'll want to look at their more in depth analysis at:
and now maybe your ready for WHO's fancy 42 page "brochure" (but too much ink is required to print it out) "Fuel for Life" at where they postulate that 1.5 million people are killed by IAP every year (or more accurately, there are many/more deaths that have IAP as a contributing factor). They discuss everything under the sun, but in the end generally have a preference for a shift to more "modern" fuels for cooking, initially those based on petroleum and then switching to more benign biofuels later. They reach this conclusion it seems after deciding that chimneys just divert smoke so that now it pollutes the overall environment, while the other possibility (in my opinion) is that we can design more efficient biomass stoves so that the smoke (a combustible gas in most cases) is burned inside the stove to extract the maximum energy from the fuel. A central problem not addressed by WHO is that modern fuels need to be purchased (and petroleum based ones are non-renewable), while the people using wood stoves tend to do so because the fuel is free or available at a low cost.

Right there you have an introduction to the health aspects (remember, almost 3 billion people rely on biomass stoves) that is almost complete enough, and you can start to investigate how people measure (quantify) IAP - smoke - and this leads you to the University of California at Berkeley (my neighborhood), one of the best places doing this research:
and here are more of their publications in the IAP area:

And we are not even going to talk here about the impacts of poor quality cooking stoves on deforestation, sustainability, and the potential for global warming:
In the end though, all of these things are related - they all affect quality of life; but the term "IAP" just refers to health issues.

With that, we'll assume that you know why IAP stoves are an important issues, and start to talk about how we can design and implement more IAP stoves!

Friday, January 18, 2008

What is an IAP Stove?

Stoves for reducing indoor air pollution come in two different types - those which have no chimney (so may be intended for use outside, or use a clean enough fuel or design so that if they are inside they need no chimney) and chimney stoves - which evacuate the combustion products from the home. Consider a chimney to be a self powered, passive (no fan needed) smoke removal device - hot air rises, and this drags the smoke up and out too. By facilitating a change to stoves which use a more technologically advanced heat source - ethanol, propane, plant oils, or even electricity - we can usually do without a chimney, but in most situations this is not an option... much of the world will continue to depend on biomass (wood, agricultural waste, and charcoal) for the foreseeable future.

A very common feature of chimney stoves is that in them the fire tends to be totally enclosed - this is how the unburnt smoke is collected and directed up the chimney and out of the house. Without these two things together (as they are in a western wood heating stove as well) you risk having smoke escape into the kitchen - an unacceptable situation. You can put a "hood" (usually sheet metal, maybe with a fan to draw off the smoke) above any non-enclosed stove and perhaps achieve the same IAP goals, but a chimney attached directly to the stove can be much easier to construct than a separate ventilation hood.

Now that your picturing the basic design - enclosed fire plus chimney to the outdoors - next the materials of construction are an important consideration. In the west we are familiar with cast iron and thick steel walled stoves, resulting in a very heavy and expensive stove that provides space heating as well as the cooking function. But metal is very expensive (~$2/kg), not usually easily available where IAP stoves are needed, those customers may not need space heating from their cooking stove so fuel is being wasted, and these types of homemade stoves don't tend to be the most efficient designs. IAP stoves for cooking should be made from all locally available materials, be suitable for construction by local craftsmen, and use just a little fuel as possible. This tends to lead us toward masonry stoves, since nearly every region has supplies of cement (for making concrete), brick, stone, sand, and similar non-metal construction materials - and building with them is familiar to local people. Certainly you will find that commercial IAP cooking stoves in developing countries are often made of sheet metal for the exterior - you can't ship any but the lightest masonry stoves (such as the ONIL, a concrete stove) - but that raises the cost significantly, as does transportation from factory to homes.

For a very locally made stove now we're picturing this concrete/brick/stone box (it can be any shape or size) - and it may be for a home, a restaurant or business (such as a tortillaria), or for institutional use (a school, hospital, orphanage, prison, etc. And it has a chimney, to get the smoke out of the kitchen - admittedly we may just be exporting the smoke so that it is now some one else's problem (I saw this recently in Xela, Guatemala where all of the restaurant stoves in the central market are wood burning, creating a haze over the whole town). We'll discuss later how better stove designs also burn the smoke when used properly, so that there are minimal emissions from the chimney as well.

Thursday, January 17, 2008

Rocket Stove Principles

The "Rocket stove principles" (see also and the references at the bottom) were develop by Larry Winiarski and the good folks at Aprovecho (for example, and they tend to be a good start for understanding how to build a stove that burns the fuel efficiently - though other design features are always being explored, and since it is just as important for cooking that we transfer the heat produced by the fire to the food, measuring the overall stove efficiency (such as using the Water Boiling Test, a calorimetry technique done by just boiling water while taking into account the estimated energy contained in the fuel) does not tell but so much about fuel burning efficiency.

The principle most significant for this discussion is perhaps the mandate that we lower the effective thermal mass around the combustion chamber, so that this part heats up fast and gets as hot as possible - so that emissions (at the top of the chimney) are as low as possible. High temperatures and the right amount of air results in burning of the smoke (fire is very simplistically the oxidation of carbon, turning it into CO and CO2, and since we don't want the CO and it is a wasted energy if it escapes, then we need to burn this to make more CO2), increasing the efficiency of the stove - with all the attendant benefits that result from this.

An issue that we don't have with single pot stoves (these are used in many, many parts of the world, where people cook outside so IAP is not an issue and the single pot is exposed directly to the flames) is that plancha type stoves can be used with several cooking pots at one time so the efficiency of the stove is even harder to measure because it depends on how many pots are on the plancha and the efficiency of heat transfer may not be as good because first the plancha is heated, then the pots are heated by the plancha. Imagine if you only have one pot on the plancha, and that it is very dented on the bottom - you are heating up the whole plancha for just this one pot (heating the room mostly - not always a bad thing) and the lumpy pot bottom will keep the food from cooking as fast. As far as I know there is no test method for determining the cooking efficiency of plancha (multi-pot) stoves so I want to try to work on this, even if just involves calorimetry using as many pots as the stove top will hold.

The locally built masonry stove that will often be discussed here (and many of the metal enclosed versions as well) are what I also call Justa-type stoves, after the name of one of the first stove types to use these general principles. You can Google on this name and find more resources than this page - for example here are building instructions used by the Honduran Development Association (AHDESA) in the past, who work in cooperation with Trees, Water, People.
and here is a 20 minute video:

IAP Stoves Around the World

Tuesday, January 15, 2008

Monday, January 14, 2008

IAP Stove Building in Humanazana, Peru

The engineers from EWB-Princeton have a great step-by-step guide to how they built the Justa-type (an enclosed masonry stove, with a chimney, used particularly for reducing indoor air pollution in Central and South American countries; often using a steel plate/griddle/plancha on the top for multiple pots) stove in Humanzana, Peru (Summer 2007).

Some small details about building any new stove (even now, every stove project is new) are particularly appropriate and important for realizing all the performance for this general design. For this type of stove you want:

  • a very intense fire, to burn the smoke
  • high temperature materials for the firebox
  • a low outside surface temperature
  • ways to make it so that it can't go wrong during operations
  • a design that will burn anything, and always completely
  • minimum ash and emissions, and maximum heat to the pot
  • can cook several dishes at one time
  • can cook some dishes directly on the metal top - breads, etc.
  • almost completely local materials when possible
  • as little heat going out the chimney as possible
  • construction just as simple as possible - foolproof
First you have to strengthen and generally improve the stove building site - I expect that you might regularly have to plan on spending time resurfacing the stove base platform, and often with the whole thing still hot from the last meal cooked. We tried to scrape this one out to a stable position, then packed it closely with stones, filled in the spaces with cement, then smoothed over the top until it was level and smooth - we might as well do a good job. Its easy to lay out the stove blocks where the nrw stove will go - it makes everything much more obvious. Everything is as hollow as possible, because solid structural things have a high thermal conductivity so we want hollow space that we can fill with better things.

After I left they made a great change by building the chimney first, while nothing else was in the way - it is made out of big 4X2 bricks, where some of the vertical shafts are hollow (200 cm2) and 2 or filled with stones, cement, and steel reinforcing bar to provide good stiffness. With the chimney as a locating point, the walls can be laid and another brick used as a spacer on the other end - clumsiness in locating the blocks can lead to lots of times wasted when you fix them together with mortar, so arrange them first.

The chimney just starts off as a leveled space where the special first brick (with holes punched it it for the gases) is sunk into wet cement and leveled, the reinforcing bar is inserted and small rocks are used as used as fill, cement is poured in regularly to fill the porosity between the stones, another brick is lowered down the steel bars and it goes up one brick at a time (30 cm each is this case). The brick is very porous so we soaked it with water first, mortared the "web" sections, then filled mortar into the gaps on the outside.

The bricks of the "wall" (you have to give names so that you can communicate fast in 2 languages) have to be attached to the base using "filet" joints that I know of from woodworking. You are attaching a flying buttress joint on both the inside and outside bottom joints on the wall - you just use your finger to make a nice big concave bead at the base; even though the stove is held together in many ways, this is the only place where it is secured to the platform. The wall bricks are also attached to each other with a layer of cement, and again it is very important to apply water to all brick surfaces before adding cement.

With the walls and chimney in place you start to insulate the hollow bricks - you want your stove to be as hot as it can be on the inside (for complete combustion - very little smoke or ash remaining), but as cool as it can be on the outside surfaces (so that it does not burn family members who happen to touch it). Sifted wood ash is a good insulator - non-combustible, lightweight (lots of air spaces), and non-compacting - but it is not as easy to find a large supply as one might think, so we use it sparingly, only where the temperatures are the highest. Around the combustion chamber and at the very top of the stove are the only places that may justify ash, so fill the tubes toward the front of the stove only with ash, and then the back ones are filled first with lower grade insulators (like crushed brick) and then topped off with ash for the last 10 cm (the hot gases in the stove will only be at the very top, right underneath the plancha. Save room at the very top of each tube for a few centimeters of coarse gravel - the cement that seals these and makes the top of the stove will not stick to ash, but it will anchor itself to the small rocks.

Now you create the top surface by applying a layer of cement across all the tube tops, checking regularly to make sure that it is level. You have to balance aestetics with productivity to create the best look without an unreasonable amount of effort - 1 cm thick is enough, then use a wet glove to create a smooth surface and rounded edges. The metal plancha is now carefully pressed into place - your initial careful measurements will result in it overlapping the wall bricks by ~1 cm on all sides, and by pressing it into the cement you will make a "lip" that both positions the plancha and seals it so that hot gases won't escape. Leave the plancha in place long enough for the cement to set well, but remove it before the plancha becomes permanently attached.

Now how do you show your cooks how to use this new type of stove properly, make sure they understand your instructions, are prepared to use these with their own local dishes, and can troubleshoot any possible problem that may arise? Consider starting by demonstrating cooking on a demo stove, in public, so that you can answer questions and demonstrate some of the benefits - no smoke in the kitchen, little or no smoke out the chimney (the smoke is burned), a cool outer surface that is safe for children, retained heat that keeps food hot after the fire is out, space for several pots with different temperatures depending on how they are placed, and so on. One thing that you can´t show them quickly is how much wood is saved by using this stove, compared to their old one - even stove engineers cannot tell you what the savings are yet, since they are hard to measure (cooking the same meals both ways is required, and tests should be conducted several times to get decent statistics). Remember that fuel savings may not actually be the strong point of this type of stove - it is designed primarily to reduce IAP, and everything else may turn out to be secondary. This type of stove is not meant for single pot cooking if it is to be efficient, since if the plancha surface is not full of pots, the empty spaces are just radiating heat out into the room instead of being used to cook food - this comes from burning wood which is not used efficiently.

Thursday, January 3, 2008

Stoving in Peru - Lessons and Observations

For some of the nitty gritty of real stove building issues in Peru - mostly involving cultural issues instead of technical problems - see my more general blog:

Wednesday, January 2, 2008

Tuesday, January 1, 2008

Friday, December 21, 2007