Project data

The Appropriate Infrastructure Development Group (AIDG) promotes affordable and environmentally sound access to electricity, sanitation and clean water. Through a combination of business incubation, education, and outreach, AIDG helps people get Access to technology that improves quality of life. Until 2010 AIDG Guatemala carried out technical R& D on the Rocket Box and other products designed for the local market.

AIDG's development of the Rocket Box stove was undertaken to alleviate the problems created by open fire cooking in rural Guatemala. The health, environmental, and economic costs of the traditional open-fire method of cooking have been widely documented. They include respiratory illnesses and accidental burns; the financial burden and time to buy or gather fuel; and de-forestation. AIDG's work to design the Rocket Box has a context in the widespread initiatives by NGOs to promote efficient cook-stoves in Guatemala.

The aim of AIDG's stove programme has been to develop a product for the market that caters for Guatemalan families' traditional cooking habits, and is affordable to them. These are necessary conditions for the Rocket Box to effectively contribute to solving these social problems. The design also seeks to maximise fuel efficiency and allow smoke to be removed from the house.

After several iterations, the result of the project is the Rocket Box stove, a metal-bodied stove which incorporates the Rocket combustion chamber into a portable and attractive 'plancha' stove. A 'plancha' or griddle is usually a feature of Guatemalan cook-stoves allowing the preparation of corn tortillas.

The Rocket Box is a portable wood burning stove. It uses a Rocket combustion chamber for high-efficiency combustion and pumice as insulation to make sure that the heat goes only where it is needed. The combustion chamber is made of baldosa tiles. The body is sheet steel. The plancha is 18" wide by 24" long, and has removable rings to allow direct contact of the flame or hot air with the pots or pans being used for cooking. A large front ring allows food to be bought to a boil and two smaller back rings are for simmering/ keeping food warm. Pumice stone is a natural resource in Guatemala. It has a low density and there are air gaps in the stone itself. This air acts as an insulant meaning the heat operates directly on the plancha.

An important feature of the Rocket Box stove itself is a grate for the wood to sit on inside the combustion chamber. This allows air to flow underneath the fuel. Without it the stove takes longer to heat and uses more fuel.

Unitil 2010 Rocket Box was manufactured and sold by AIDG's local partner, Xelateco.

## The good

Tortillas made on the Rocket Box are delicious. The stove enables a cook to be versatile, with the potential for many dishes to be perfected such as vegetables 'a la plancha'. Multiple dishes can be cooked at the same time on the pot rings with tortillas on the plancha.

Many Guatemalan households, in urban areas as well as the country, still rely on an open fire. The fire is often built on a platform of sand/ stone with two or three cinder blocks; metal struts are used to balance the cooking pots in between the blocks. It's known locally as a 'pollo.' The Rocket Box removes smoke and other harmful gases from the house via a chimney, vastly improving inside air quality. Other Rocket stove designs do not have a chimney. Some improved cook stoves promoted by NGOs in Guatemala are of this kind, for example the ONIL Nixtamal stove: http://www.onilstove.com/. This is promoted for use in addition to the ONIL stove with a chimney, where additional cooking capacity is needed.

The Rocket Box is very economical with wood consumption compared to an open fire and other commonly available cook stoves in Guatemala. Water Boiling Tests were conducted by AIDG in 2010 on the Rocket Box and a typical metal plancha stove commonly available in Guatemalan hardware stores. The comparison stove body was empty on the inside apart from a ½" lining of bricks. The tests indicated a thermal efficiency of 15 – 21% for the Rocket Box (depending on the type of test) and 5 – 8% for the other stove.

Stove efficiency also compares favorably with some other improved cook-stoves promoted by NGOs to reduce fuel consumption. There is debate over the efficiency of ramp combustion chamber stoves for example (Boy, Bruce and Delgado, writing in Environmental Health Perspectives. Jan. 2002.)

As well as using less wood the Rocket Box can reduce cooking time. In the tests 2.5l of water (with no pot lid) boiled in 25 minutes on a Rocket Box, the stove started from cold. On the comparison plancha stove, 2.5l boiled in 63 minutes.

The stove's mobility is convenient; it is not uncommon for families in Guatemala to move their kitchen to a different part of their property as the years go by. It is relatively lightweight (around 60 Kg.) Its attractive appearance is popular. The main body of the stove does not become dangerously hot, reducing risk of burns.

## Current model specifications

Dimensions for the stove body, plancha and combustion chamber are given in the Rocket Box design document, published on www.aidg.net.

This stove is designed around a 60.8 x 46cm plancha. The box is sheet steel riveted to an angle iron frame. The bulk of the frame is constructed of 1"x 1/8" angle iron, welded together. The body is 24 gauge galvanized sheet steel.

## Combustion chamber

The height of the chamber tower should be 2 or 3 times that of the height of the entry to the chamber. The combustion chamber mouth is 14cm high by 12cm wide. Therefore it's important to ensure that the height of the chamber tower is between 28cm and 42cm. A 1: 2½ ratio seems to work best. This is to help ensure a good draft and efficient burning.

Heat is strongest at the point of the flame. This means the combustion chamber tower should be high enough for the flame to almost touch the plancha. With a 48cm wide plancha, a 3.5cm space should be maintained.

The firewood is held off the floor of the combustion chamber by a grate, originally made by welding 3/8"rebar (this thickness has since been reviewed). The height of the grate is equal to 1/3 of the height of the combustion chamber. This allows sufficient air to pass through to create an effective draft. The stove footprint is 60.8 x 46cm x 32.3 cm high.

## Product development history

The AIDG improved cook-stove R&D programme investigated several different stoves before focusing on the Rocket Box. The first stoves to be tested were built from masonry, with early iterations following the ramp or 'baffle' design, with a generous cooking surface. These plancha stoves are built on a cement/ cinder block base of cement filled with dirt. The top levels are built from brick and the combustion chamber ramps up from the front to the back of the plancha, until only eight centimeters remain between the floor of the chamber and the metal plate at the back of the stove. A smaller internal volume means that the heat generated by the fire travels more directly to the metal plancha.

In 2006 AIDG organized a Teco-Tour initiative. This included stove building by travelling volunteers. The Teco-Tour Stove was described by AIDG's Elena Kreiger "the design put a rocket stove baldosa tile combustion chamber into the Pop Wuj stove body [the Pop Wuj stove is a typical baffle stove with a masonry body]... The combustion chamber...design [is] like that used in the ONIL stove." It was insulated with pumice stone.

The ONIL stove is very similar to the Rocket Box. Instead of a metal stove body precast concrete is used: http://www.onilstove.com/. During Elena's interneship AIDG investigated the effects of designing the ONIL stove with a longer plancha, increasing cooking area. Howevever working with precast concrete was problematic. The combustion chamber of the current Rocket Box still owes credit to the ONIL stove. The transformation to a metal stove body was made partly as this allows the stove to be mass produced in a basic workshop, avoiding on-site building. This benefits AIDG's development model of supported businesses.

In 2009 Ben Dana and Sarah Hunt experimented with a Rocket Box with the combustion chamber 5cm longer, in response to customer feedback. Water Boiling Tests 7 – 16% thermal efficiency compared to 15 -21% for the standard Rocket Box. Cooking time was increased with 56 minutes to boil 2.5l water on the modified rocket box, compared to 25 minutes on the standard model. However, heating on the back cook-ring improved with a longer combustion chamber.

The Rocket Box Design Manual outlines customer feedback following research at Nueva Allianza village in 2009. A few design changes were made in response. The 28 gauge sheet steel elbow connection to the chimney was replaced with 26 gauge steel. The fire grate was changed to thicker bar.

In 2010 the AIDG Guatemala's Tec R&D Section became an independent organization in its own right, Alterna. The final Rocket Box incarnation of the Rocket Box, under its auspices of Alterna, followed market research directed by Daniel Buchbinder to ascertain design preferences. Information on the modifications is not available and has not been included in the Rocket Box Technical Documents. Changes are thought to include more space in the combustion chamber, an increased area for pots to stand on, and improvements to back cook-ring heating. The stove may also have a different name. Contact scrowe@alterna-la.org

## Information for action

There are four documents we are presenting in relation to this technology. There is a design manual, in English and en Español. There is also a fabrication manual, also in English and en Español. They are published on www.aidg.net  Technology files  biomass http://web.archive.org/web/20160827193514/http://www.aidg.net:80/index.php?option=com_remository&Itemid=34&func=selectfolder&filecatid=18

The design manual outlines the different options that were tried or considered, why some were discarded and the current design selected, a detailed presentation of the current design, and suggestions for future work. The fabrication manual is a step by step guide to manufacturing the stove. The film, 'How to Build a Rocket Box Stove' can also be viewed on http://www.youtube.com/watch?v=hkFqpkV3fF4

Page data
Type Project rocket stoves, portable wood burning stove, portable stove, rural, metal, baldosa tiles, wood, pumice stone, galvanized sheet steel, angle iron SDG03 Good health and well-being, SDG07 Affordable and clean energy, SDG11 Sustainable cities and communities Ben Dana 2011 CC-BY-SA-4.0 No main image Ben Dana (2011). "The Rocket Box Stove". Appropedia. Retrieved August 7, 2022.
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