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close this book Boiling Point No. 04 - March 1983
View the document Acknowledgements
View the document Editorial
View the document Nepal - The CFDP / RECAST Stove Programme
View the document BP No. 3: New Nepali Chulo
View the document Gambia National Stoves Project
View the document New Stoves in Senegal
View the document Stove Seminar in Bamako
View the document Alternative Cooking Stoves Zimbabwe
View the document Evolution of Insulated Stoves in Kenya
View the document Improved Stoves in Niger
View the document Avoiding Pot Holes in the Structural Design of Pottery Stoves
View the document Radiation and Stack Losses
View the document Reviews
View the document Focus on Testing
View the document BP No. 3 Village Studies in Sri Lanka
View the document Mud Stoves in Malawi
View the document ITDG stoves project manager
View the document Intermediate-Technology Development Group

Evolution of Insulated Stoves in Kenya

by Bill Stewart

ITDG Stoves Project

In 1981 and 1982 a considerable amount of publicity and effort went into the promotion of the need to produce more efficient charcoal stoves for use in Kenya.

One approach was to try to introduce the Thai bucket stove, an insulated pottery liner stove. In 1982 Max Kinyanjui, working with the Ministry of Energy and two other Kenyans from Clayworks, a private brick and tile company, went to Thailand to study the production system for the Thai bucket stove. On their return they worked on adapting the stove and production system to Kenyan conditions.

A number of design changes were made by Max Kinyanjui and others to the stove, to make it more appropriate. A tight fitting door was added so that the heat output could be reduced for the longer simmering periods of Kenyan cooking. To make the stove more robust, the bucket was made cylindrical instead of tapering, and metal stands were used instead of pottery stands to support the-pots.

Production of 500 of these stoves was then begun at a medium sized pottery workshop. The pottery liners were made at the workshop, the metal shells were made by traditional artisans. Insulation materials were bought in, and the whole stove was fabricated at the pottery workshop.

The final cost of the new stove was about 67 Kenyan Shillings (US$6.70) compared to KSh 20 (US$2.00) for a traditional charcoal stove. Laboratory tests showed that the new stove was faster and had fuel savings of about 30%. For an urban household using charcoal, the extra investment would be paid back in less than two months. However, the difficulties in organizing the various craftsmen for the stove production, the heavier weight, the problems of transporting the stoves, and the higher initial cost to the consumer, made it worthwhile to investigate other types of stoves and production methods.

Following the success of the introduction of charcoal stoves lined with cement and vermiculite in Papua, New Guinea, it was decided to adapt and test this stove in Kenya.

Vermiculite is a lightweight rock that is produced by heating a type of mica so that it expands to about 10 times its original volume. Both vermiculite and cement are products of Kenya, and when mixed, a lightweight, easily moulded, heat resistant material is produced which can be used to insulate the stove instead of pottery liners. A mixture of vermiculite to cement of 3:1 produces a material with a density of 0.8 gm/cu m. Max Kinyanjui, with assistance from ITDG, designed a simple production procedure for a lightweight, cheap cement-vermiculite stove. A plastic bucket is placed inside a traditional metal stove and the mixture of cement and vermiculite is packed in between the bucket and the metal wall to produce a lining approximately 4cm thick.

A testing programme was then organised to test different charcoal stoves that had been developed and were in production in Kenya. m e Kenyan pottery liner stove, two cement-vermiculite stoves, four types of UNICEF UMEME stoves, and the traditional jiko were chosen for testing.

Test Stove Data









C-V*, top only




C-V,fully lined




Pottery liner



Pottery & ash

Traditional jiko







Metal & air




Metal & air




Metal & air






Test Procedure:

All tests were done with 300 gms of charcoal. A 12 gm piece of paper soaked with 8 gm of kerosene was put in the bottom chamber of the stove and lit. A covered aluminium pot containing 2 litres of water was placed on the lighted stove and brought to the boil. After boiling, the door was left open for high power tests and closed for low power tests. m e times taken to ignite and to boil the water were noted, and the PHU2 calculated.

The tests were repeated 4 times for the two cement-vermiculite stoves and the traditional jiko, but fewer times for the other stoves because of time constraints. The Standard Deviation did not exceed 6% of the mean PHU values for the tests repeated 4 times.





Test Conclusions:

1. The time taken to ignite did not differ greatly between all the stoves.

2. The insulated stoves are all significantly faster to boil than the traditional jiko (33% faster) significant at the 1% confidence level).

3. The insulated stoves are all more efficient than the traditional jiko, and the difference is more pronounced at a high power output (31% more efficient on average) - significant at the 5% confidence level).

4. It was not possible to lower the evaporation rate of the UMEME liner stove and the cement-vermiculite fully lined stove below 10 gms/minute, and it was not possible to get greater evaporation rates than 10gm/minute for the traditional stove.

5. The performance of the UMEME stove was very dependent on different grate designs. The model with an insulated firebox had the best performance (Fig 8).


The cement-vermiculite stove with only the top section lined, besides having a high efficiency and variation of heat output, was also the lightest, cheapest and simplest insulated stove to produce. Because of these positive attributes a small production system was set up to produce the stoves. In November 1982 over 100 were produced to be used in a field trail. The performance of both the cement-vermiculite stove and the pottery liner stove will be monitored to see which stove and production process will have the greatest chance of success for widespread dissemination in Kenya.