Cook stoves can vary in efficiency, depending on design, as an article in the July, 1995 issue of Scientific American show. Excerpts from the article follow:
Half the world's population of nearly six billion people prepare their food and heat their homes with coal and the traditional biomass fuels of dung, crop residues, wood and charcoal. ... Combustion of biofuels contributes to the hazy pall that hands over the cities of the developing world. Carbon dioxide, methane and other greenhouse gasses from cooking fires may also foster global warming.
Since the energy crisis of the 1970s, international aid organizations have targeted the improvement of traditional cooking practices as a simple and affordable way to address the environmental, economic, and energy issues posed by the home fire. ... Over the past decade government programs, development assistance groups and community-based organizers have undertaken a thorough review of the requirements for successful dissemination of cookstove technology. A new generation of stove programs is now implementing these hard-won lessons. This effort encompasses everything from an examination of stove thermodynamics and materials science to market research and grass-root educational campaigns.
Almost one million households now cook with the Kenya ceramic Jiko. The Jiko - the word means "stove" in Swahili - consists of a metal casing with a ceramic lining that helps to direct 25 to 40 percent f the heat from a fire to a cooking pot. The traditional metal stove that the ceramic jiko replaces delivers only 10 to 20 percent of the heat generated to a pot, whereas an open cooking fire may yield efficiencies of as little as 10 percent.
Even more fundamental problems plagued some of the early prototypes. Designers acted as if it would be an elementary exercise to improve the efficiency of the common metal stove, a deceptively simple canlike enclosure into which charcoal or wood is fed and ignited. In fact, after much trial and error, it turned out that an extensive investigation of stove physics and engineering design was needed. This analysis revealed that the largest loss of heat from the fire, about 50 to 70 percent, occurs from radiation and conduction through the metal walls.
The design of one early improved jiko model emerged after an aid group named the Kenya Renewable Energy Development Program sponsored a research trip to Thailand to inspect an improved stove - the Thai bucket. The resulting jiko design had inward-sloping metal walls, like the Thai stove, as well as an insulating liner made of ceramic and a mica called vermiculite.
Higher efficiency cookstoves have been adopted throughout the developing world. China has by far the world's most extensive program, with more than 120 million stoves in place - seven out of 10 rural households own these units. ... The Chinese stoves, which burn wood, crop residues and coal, consist of a brick and mortal construction with a chimney that fits in the central living area of a home. An insulating material, such as ask and mortar, is packed around the circular cast-iron opening, which holds a wok.