Stove Built!

For the past few days, we have worked with Bernard to build another stove, incorporating design modifications inspired by DHE stove development on campus, PFD’s Jiko Bomba, and Bernard. Although the DHE group on campus developed a really cool method of lighting the stove based on the technique used for three stone stoves, both Bernard and Didas felt it was important to avoid using firewood and emphasized that obtaining kerosene and matches would not be an obstacle in Arusha or its outskirts. Therefore, we opted to deviate from the designs of the stove built on campus and create a new design.

Our first modification was creating a mechanism to control the primary air. To do this, we drilled more holes in the center of the base plate than on the outside, as compared to the original stove. Then, we created a disk that with the same size and alignment of holes as on the base plate. We used a screw to attach the centers of the base plate and disk. The disk can be rotated with a handle extending between the two legs at the bottom of the stove. Depending on the disk’s orientation, the holes of the disk and the base plate align and allow lots of air to flow or are closed and allow little air to flow. This is best seen in these pictures:

Primary air holes completely open

Primary air holes completely closed

The aim of this modification is to regulate the size of the flame so that the fuel can burn hot and fast for boiling water or slower for cooking beans or other foods. We were inspired by the gate on the Jiko Bomba which allows the used to adjust the amount of primary air. 

A second modification we made was to help users mix the sawdust or coffee husk to maintain a good flame. We noticed the fire would decline and eventually start smoking unless we stirred the fuel with a stick. The stick stirring strategy worked but is not feasible if a user is in the middle of cooking a meal. To fix this, we bent two sets of wires into this shape:

These wires are then inserted into the bottom holes of the stove and can be rotated in order to stir the biomass.

A third design modification we have made is to create stands coming out from the chimney as a pot holder in place of a pot skirt. This reduces the amount of sheet metal needed and to make the stove. More importantly, it makes the stove compatible with all different pot sizes. Various NGOs and people we have talked to say that there is no standard pot size and that the size will differ by family size and food being prepared. However, this no-pot-skirt modification does sacrifice some stove efficiency.

Additionally,  we added guides on the outside of the fuel canister in order to ensure that the outer shell is roughly equidistant from the fuel canister around the full circumference. Credit here goes to Bernard.

Building the Stove

After discussing these modifications with Bernard, we began to build the stove. We bought an eight foot by four foot long piece of sheet metal for 60,000 shillings and then paid another 2,000 shillings to get it delivered to the workshop. Bernard had tools and other scrap pieces for the feet, so this is all that we needed to buy. According to our calculations, it is possible to make exactly three stoves from one such piece of sheet metal. This number depends on whether we build the taller stove, the most recent stove design received from the stove group in Hanover or the 10 cm shorter version we carried with us to Tanzania. We built the taller stove so that we could price out the most recent design and see whether the taller fuel canister will permit longer burn times.

Bernard showed us how to cut the sheet metal and then Misha and Julie Ann did the cutting. Next, Bernard smoothed the edges and cut the circle pieces out. We all worked on bending the thicker sheet metal into a circular shape, and Bernard welded the pieces together and smoothed them out. After that, we marked where we’d like the holes drilled and Misha and Julie Ann drilled the holes as Bernard instructed them. Julie Ann and Ayushi marked where to cut the mixing tabs on the inner canister of the stove while Misha finished drilling the holes.

We returned the next afternoon to continue measuring out pieces for the handles, pot holders, and primary air controller, all at 3 cm by 30 cm. Misha then cut out the marked pieces. Julie Ann and Ayushi worked on marking out how many stoves a 8 foot by 4 foot piece of sheet metal. As mentioned earlier, we discovered that one piece could make three stoves and then some. That means that the material costs for each stove amount to 20,000 shillings. This number, however, does not account for the material needed for the legs or stirring rods.


After Misha cut out the last few pieces, Julie Ann and Ayushi worked on bending the pot holders and handles. Bernard then began welding the stove to conclude our day's work.  We returned on Monday and added the legs to the inner canister of the stove. Bernard used some spare square shaped tubes of metal. He welded them to the outside of the canister so that the outer shell would be elevated approximately 1 inch to allow for more secondary air. We also made two makeshift stirrers out of a piece of wire. 

We were very proud to have completed the stove after two full days of work! It has been a pleasure working in Bernard’s studio. This is our final product:

The stove disassembled:

A detailed drawing with dimensions etc. will follow.

Testing the Stove

For the first test burn, we used larger sawdust and filled the canister about half way. The burn lasted about a half an hour, required no tending, and was very clean. The embers were still hot for another 20 minutes. It took about eight minutes to bring 1.5 liters of water to boil. Next, we tested a mixture of sawdust comprised mostly of fine sawdust and filled the canister all the way. We inserted a cylinder of expanded sheet metal on top of the hour glass shape to allow the fuel canister to be filled all the way. We were hoping this would increase the burn time as well as efficiency, thinking that more sawdust at the top would provide insulation. Unfortunately, this burn was rather smoky at times, required tending, and burned for 80 minutes. We used to IAP meter for this burn but have not yet analyzed the data. We believe that the sawdust used for the second burn was too fine and that there was not enough room for air to flow through the fuel bed. 

During these tests, we realized the importance of having a consistent fuel source. The type, size, and moisture content of the biomass have a large effect on the quality of the burn. It was difficult to compare the effects of the stove modifications when the fuel source was so different between trials. We discussed selecting only one loose biomass and focusing all our efforts towards optimizing the stove's performance for that one fuel. Later, it would still be possible to explore the stove's performance with other fuels.

As we were nearing the end of our final burn, a man on his way home from work stopped to watch. In a conversation mixing broken English and even weaker Swahili, we shared his enthusiasm for our stove, inquiring multiple times what it costs and where he could get one.