Several testings were executed in Aprovecho (research lab in Eugene, OR) using briquettes made of sawdust and paper (app. 70%sawdust, 30% paper). Primary goal was to test different stoves and see where briquettes perform best; overall 6 different stoves were tested, but 3 basic forms distinguished: 3-stone fire (open fire), top-feed burning (like they’re usually burnt using stoves) and side-fed briquette with the new ‘Rocket’ prototype.

With Portable Emission Measuring Sytstem (PEMS), it was possible to read the levels of CO2, Carbon Monoxide (CO) and Smoke/Particulate Matter (PM) on the computer screen during the testing process and examine specific patterns of burning. CO was very important since represents one of the most dangerous emissions and cannot be tested without lab equipment.

With all stoves 1 liter of water was boiled as soon as possible and simmered as long as possible using app. 3 briquettes (3x100g-130g). Here are some general patterns that were recognized after 30 briquettes were burned in different settings:

Whats recognizable for all stoves?
1. In the phase of the burn when briquettes are loosing power (when there is no more fresh material left in the briquette) the CO levels get higher making a dangerous burn, especially with open fires. When we stop with cooking, its much better to intentionally stop the fire or close the stove door to limit the excess air than leaving the fire unattended! We can use the remaining ashes and unburned briquette material as a great fertilizer – biochar.
2. With all stoves we were able to boil one liter of water in 10-11 minutes in just few tests. That proves all forms of burning the briquette are powerful enough.
3. The best time (for less CO emissions) is to insert a new briquette when the previous one in burning throughout its mass (no fresh mass left; this can be seen by the porous texture)

3-stone fire

1. Briquettes burn fast and powerful (through their own holes) and when they get on fire, there is not a lot of smoke any more, but CO level is always high – the gas doesn’t burn out without the extra combustion chamber.
2. Bigger holed briquettes (2 inch hole) burned much faster, while the small holed briquette (1 inch hole) lasts for long, with a steadier fire. if people would like faster burning briquettes with 3-stones or if a slow burning material is being used (like the water hyacinth for example), it might be suggested to try to enlarge the hole.
3. 3 briquettes were used just to boil the water, then the power went down. Comparing to other stoves, it makes it a fast, but very fuel-consuming ‘stove’.

Top-Feed Stove
1. When we insert a new (cold) briquette on the fire from top, the CO level rises very quickly, also smoke if we have no combustion chamber (Jiko stove). It also makes it impossible to control.
2. We don’t have the visual control over the fire (in a closed combustion chamber, like the China Stove) and have to lift the pot to insert a new briquette.
3. Its good since we can use wood sticks, even logs with this type of burning, but this surprisingly also rises CO levels. More tests should be made to figure out efficient hybrid fuel usage (wood + briquettes).

Side Feed Stove
The testing with side-feeding of briquettes showed very promising results, especially in low CO emissions. Like in 3-stone fire, some of the gases are burned already in the briquette’s own ‘combustion chamber’, but with the stove, the burn then continues through the insulated liner of the stove, making it very clean.

1. Start is very non-smoky since the briquette is burned gradually just from one side – not all of the cold mass is bumped on the fire at once. Chilling the fire makes smoke and CO.
2. We can additionally control the volume of the fire by partially closing the side feed with the door, but the door need to be tightly fitted to the inlet hole.
3. To minimize the CO emissions in the last phase, we completely shut the door, enabling the combustion chamber to retain the heat and slowly burn out the briquette.
4. When a new briquette is inserted, the CO went down, which was a surprise (happens just the opposite in other stoves). This needs to be tested more, but could work acc. to prolonging the combustion chamber (in front) that gases burn out better.

These are all still hypothetical results based on observation, although with scientific measurement system. There were not enough tests made to officially represent the results with numbers. Strong patterns were being recognized instead that can suggest more appropriate ways of burning this alternative fuel that has lots of potential still to be discovered. Feedbacks from the field are most appreciated; if there are some info that you not agree with, or would like to know more about, please respond to this article or write to the author on email: rok.stoves@gmail.com

Rok Oblak

January 2009
Aprovecho Research Lab, Eugene, OR

18 thoughts on “Testing

  1. Rok, I would like to experiment with the bio fuel stoves for groups of chronically homeless populations in Austin Texas.
    I hav the manuels from Legacy Foundation but would like to have an example of a stove and briquettes before I go much farther. Do you or anyone else sell them in the US?
    I would also be interested in any examples of selling the fuel and stoves in developed conutries. Thank you for your help!

    1. Hi Bob, thanks for your inquiry. There are no briquettes or briquette stoves for sale in the US that I’d know for, but if you’re up to it, I can help you make one. There is a video-guide on youtube which instructs you to make a stove in one hour + firing in a kiln when it’s dry. You can also make it out of metal if you prefer the material, but the ceramic stove is more efficient due to insulation properties.


      Take a look at the videos and see if this would work for you.


  2. Hello Rok,
    I am planning to build a prototype rocket stove that burns briquettes together with wood.
    I have some questions concerning the briquettes used in the side fed/rocket stove tests at aprovecho (and also in your lentil cooking video)
    You mentioned the composition (prox. 70% sawdust 30% paper) and weight (100-130 grams?), but I would would very much like to know the dimensions; external briquette diameter,
    hole diameter ( 2 inch ?) and briquette length in both the aprovecho photos and lentil video. Also, with these dimensions; about how many minutes did the briquettes burn before no more fresh material was left.
    Thank you in advance for answering my questions.
    -Daniel Roggema

    1. Dear Daniel Roggema,

      many tests have been performed with various briquette dimensions and it ended up with 4inch (10cm) external diameter and app 2 inches for internal, but this usually varies a bit since there are different standards of pipes around the world. The inner hole diameter is very important – if you have it too big, there’s too much airflow (cold air hitting in the combustion chamber) and too small would choke the fire. It also depends on the briquette/fuel material (faster burning or slower). The outer diameter needs to be app 3-5mm smaller all the way around comparing to the stove opening.

      Briquette length is also important: when you start the fire, you need at least 2 briquettes pushed in the stove since the gap inbetwen will keep the flames going (before the combustion chamber gets hot), then you can continue with one or whatever output you need (more briquettes – more fire). My briquettes were app 3 inches long or even 2.5.

      Briquettes burn app 20 minutes (of high output, than slowly dying, so if you add another briquette the first would last till the 3rd is inserted..), again depending on the material.

      Hope this gives you some useful answers! Good luck with building stoves, I would be interested to see the results if you want to share them!


  3. Rok,
    I am a US Peace Corps Volunteer and Masters INternational student posted in Bale Mountains National Park Ethiopia. One of my projects is working with Frankfurt Zoological Society on their Legacy Foundation fuel briquette project. I am considering making briquette burning stoves a thesis. I would like to test designs that others have made and a design of my own that can be made with locally available materials, similar to your work on this page. Can you provide me any information on construction techniques you have used for your ceramic stove and info on the Chinese stove. I have lots of the info Aprovecho and have studied stoves some in my Masters International studies. I am looking for design suggestions, people who might like their stoves tested in this context and actual tests for briquettes and stoves. Any help would be appreciated.
    Brian Barbre

    1. Hi Brian,
      there is basic information on how to make the ceramic Holey Roket stove on this website (material mixture, basic dimensions and the video how to make it) – do you want to know something more specific?


      The Chinese stove – you probably mean this one?


      You can check more info on this website. When i was trying to use it with briquettes it worked really well, but the briquette-feed would need to be better designed, i just used a sheet-metal pipe. Let me know if you want to proceed with this kind of adaptation, i think this could work out great, but there are several ways to go, depending on your local resources and needs..

      When you mention testing of other stoves – do you have a portable emission testing device? Would be great to do some tests in the field with different briquettes stoves!! I’m really curious to find out the test results in the field comparing traditional briquette burning and lets say Holey Roket stove. I’ve done testing in the laboratory, but its not the same.

      How is it in Ethiopia, do people use briquettes already or you’ve just started with introducing the technology?

      Best regards

  4. Rok,
    Thanks for the info. I haven’t had a chance ot check out the web sites yet as internet for me is a specialty. I am planning on trying to modify any tests I can find to field tests with an emphasis on FIELD. I don’t have any emission testing equipment yet but know that there are some portable devices that people have used for testing indoor air quality and particulate PPM so hope to work with that. I have access to some clay and lots of sheet metal so I have several insulation and stove mass combinations I hope to try. Apparently there are some briquette projects in Ethiopia and I am hoping to get in touch with them to work out feasibility and figure out snags that their projects have come across. I am working on this as part of the Frankfurt Zoological Societys Center for Alternative and Sustainable Technology for Livelihood Enhancement project and hope to get it up and running regardless of my thesis but would love to knock out two birds with one stone.

  5. Rok,
    One quick question. What is the best method you have found for igniting the briquettes in the stove? Are you starting a smaller fire first, or using charcoals?

    1. Hi Brian, you can ignite briquettes in several ways, but always push one or two in the stove before starting the fire, so they immediately create a good, condensed airflow.

      Its best to start the fire from the top of the stove in the middle of the combustion chamber with some sort of smaller burning particles – I propose you use whatever you’re most used to igniting fires, like some paper, twigs, parts of wood, etc. If you just want to use briquettes, you can break a quarter of one briquette into small parts and pile them up in the middle of the combustion chamber, leaving enough air around them so the fire won’t choke. It should be really easy, especially when you get used to it.

      I hope your endeavors with the Ethiopian briquette project goes well! Looking forward hearing back from you and please don’t hesitate to contact me for any other info


      1. Hi.I was wondering whats the best geometry to use for fuel briquettes. I’m thinking of having beehive briquettes but i have read here that a cylindrical one with a hole in the middle works best. I am into designing briquettes that provide optimum burning period. What geometry works best?

      2. Hi! I did many tests with different shapes of briquettes and came to a similar dimension to what Legacy Foundation and some other organizations and communities are using around the world, which is 10cm/4inch outer diameter and 3-4cm/1.2-1.6inch hole diameter (for the holey roket stove, a bigger, 4cm hole is preferred)

        I did a rectangular shape, but doesn’t work as well. Also briquettes without a hole is not good – a hole makes the flame condensed and so more powerful, it works as a tiny combustion chamber by itself, isolated from the cold air by the fuel itself.

        Whatever the shape, the key thing is to make a good airflow through the stove to the cooking pot or pan. It also depends on the stove type, pot size and shape, briquette material, etc. If you can give me more information about your tools and materials you are using i can provide more information! You can also write me on rok.stoves@gmail.com

        Kind regards
        Rok Oblak

    1. No terty, there are many centers around the world making these stoves now and developing their own technologies, which was and still is the goal of this website library. The basic idea is there and now it is on people to copy it and adapt it to their local environments

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