Guide to Designing
Retained Heat Cookers
                HELPS International
         Partnership for Clean Indoor Air

The Guide to Designing Retained Heat Cookers was written by Don O'Neal, Vice President of HELPS
International and Special Projects Director.  Don O'Neal is also the designer of The ONIL Stove and the
Stove Project Manager.

The development of the HELPS International Retained Heat Cooker was funded by a grant from the
United States Environmental Protection Agency (X831690010) to further the mission of the Partnership
for Clean Indoor Air, to improve health, livelihood, and quality of life by reducing exposure to air pollution,
primarily among women and children, from household energy use. To learn more about the Partnership for
Clean Indoor Air and the HELPS Retained Heat Cooker project in Guatemala visit www.PCIAonline.org.

HELPS International has been working in Guatemala for over 20 years. During this time, HELPS has
developed a poverty reduction program that includes the following components: curative health, preventative
health, education, construction, economic development, and sustainable household energy.  In addition to
developing a Retained Heat Cooker, HELPS has a stove manufacture and distribution program in Guatemala
that has demonstrated significant reductions in health and environmental problems. Currently, HELPS
supplies stoves to 120 non-government organizations (NGOs) in all 22 Departments of Guatemala for  their
community development projects.  The HELPS stove reduces wood usage by 70% and has a chimney that
removes emissions from homes. HELPS has an extensive training program both for the user and for the
NGOs using the stoves in their community development projects. To find out more visit www.helpsintl.org.
Photo Credits: Don O'Neal

Guide to  Designing Retained  Heat Cookers
By Don O'Neal
Table of Contents
Introduction	1

Theory of Operation	1

Advantages of Using a RHC	1

Typical RHC Components	2

Types of RHC Projects	3

The Design Process	3

Comparative Examples	4

Design Instrumentation	5

RHC Performance Objectives	6

Pre-Boiling Considerations	7

Marketing and Distribution	8

Appendix: Testimonials from the Field	9

Indoor Air Pollution from Home Cooking and Heating	11

About the Partnership for Clean Indoor Air	11


                                                                    Guide to Designing Retained Heat Cookers
 The technology of using the heat that is retained in
 a pot of boiling food to finish the cooking cycle has
 been known for more than 30 years. Historically, a
 hole in the ground lined with hay for insulation has
 been used for a "retained heat cooker." Hence the
 name "haybox" has been used to describe this type of
 cooking. The use of the term "retained heat cooker"
 is more descriptive of the general process where other
 insulating materials may be used, and is therefore
 used in this document.

 Retained heat cooking has been used in developing
 countries to minimize the use of limited firewood
 resources. However, success of this process has
 been somewhat mixed since the materials used for
 insulation have had varying degrees of effectiveness.
 The development of a retained heat cooker is an
 iterative and ongoing process.

 The purpose of this Guide is to demonstrate how
 to effectively design, test, and distribute a retained
 heat cooker in a field setting. In the following
 sections, you will learn about the benefits of using
 this form of improved cooking technology, its
 typical components, equipment necessary to test its
 performance, lessons from high performing retained
 heat cookers,  as well as tips on marketing and
 distributing a retained heat cooker in the field.  In
 the Appendix, you will also find testimonials for one
 retained heat cooker, the ONIL Cooker, which has
 demonstrated success in the market and the field in

 This Guide serves as an introduction to one type  of
 improved cooking technology that can supplement
 other cooking practices to reduce indoor air
 pollution and increase fuel efficiency. For more
 information on other types of improved cooking
 technology, visit the Partnership for Clean  Indoor
Air at www.PCIAonline.org.

Theory of Operation

A retained heat cooker (RHC) is used to efficiently
cook foods that require boiling, such  as beans and
rice.  When foods are boiled, energy (typically from
a wood fire) is used to bring the food and water to
a boiling temperature, 100 °C at sea level.  Once
boiling temperature has been reached, only enough
energy (heat from the stove) is required to simmer
the food (keep it just at or below the boiling point).
Additional energy only serves to convert water to
steam without raising the temperature of the contents
of the pot. This additional energy wastes wood and
water that may have been carried long distances.

When the pot simmers (remains just at the boiling
point), the amount of energy entering the pot
balances the energy lost to the atmosphere through
conduction, convection, and radiation.  Reduction
of the energy lost to the atmosphere results in
a reduction of energy required to maintain a
simmering temperature, hence less fuel is required.

If a perfect insulation were available, the losses could
be completely eliminated and the pot would stay
at a simmering temperature with no further fuel
required. While there is no perfect insulation, there
are insulation materials of sufficient quality to keep
the contents of the pot at a cooking temperature
long enough to complete the cooking cycle. Since
practical insulation materials do not completely
eliminate losses, the temperature decreases at a rate
defined by the quality of the insulation. Fortunately,
there are many materials with sufficient insulating
properties to reduce losses to such a degree that the
food will complete cooking without further fuel
usage. This is discussed further in the Typical RHC
Components section.

Advantages of  Using  a RHC

Since the fire may be extinguished once the pot
contents have reached boiling temperature, there
are many advantages:

^ The cook is freed from tending the fire and is
  available for other tasks

> Cooking is completed without further fuel usage

^ Cooking is completed with minimal use of water

>• The pot contents cannot boil dry or scorch

> There are no internal or external emissions due
  to the simmering phase in the RHC

^ The RHC is portable enabling workers to take it
  with them to the fields

Guide to Designing Retained Heat Cookers
A well-designed RHC provides many additional
benefits. It can be used to keep water hot overnight to
get a quick start on breakfast or to keep foods hot for
a later meal.  It is also useful for preparing foods that
require very long cooking times, such as unsoaked,
dried beans (but presoaking should be encouraged).
Food may be simmered over die fire for a period
of time, and dien placed in the RHC to complete
cooking. Alternatively, food may be removed from the
RHC, reheated over die fire, and replaced in the RHC.

Typical RHC Components
The Pot—The container for the food that is to be
cooked is  typically made of metal or clay. Clay pots
are sometimes considered less efficient for cooking,
because they have a higher thermal mass and
readily absorb heat that could be used for cooking.
However,  clay pots may have an advantage for
some cooking tasks with the RHC, because the
thermal mass retains heat that continues to cook
the food inside the RHC.

Outer Container—The material used in the
outer container contributes little to the thermal
performance of the RHC if the insulation is adequate.
Its primary purpose is to support and contain the
insulation and make the RHC easy to handle without
damage. In its simplest form (but quite unhandy), it
can be a hole in the ground that holds the insulation
in place. A woven basket that has tight enough weave
to retain the insulation can serve. However, where
possible, the following should be considered in
choosing the outer container:

 ^ Durability

 ^ Easily moveable

 ^ Moisture, mold, and mildew-resistant

 ^ Ease of cleaning

 ^ Provisions for picking up the unit (handles)

 ^ Room  for extra insulation below the pot

 ^ Attractiveness

 *• Resistant to tipping over

 > Safety
Insulation—The purpose of the insulation is
to retain the heat of a boiling pot long enough
for the contents to complete the cooking cycle
without additional heat. There are many choices
for insulation and choices will depend on what is
available locally.  Some choices are:

> Hay
 ^ Leaves

 ^ Newspapers

 >• Corn shucks

 ^ Corrugated card board

 > Wool blankets

 ^ Styrofoam and other commercial insulations

 ^ Pumice

 * Ash

 *• Perlite

To be effective, insulation must be dry, resistant to
mold and mildew, and must not compact with use.
If insulation (such as hay) is not resistant to mold
and mildew, there must be an adequate supply, so
the insulation can be replaced frequently.

Inner Container—The inner container sits inside the
insulation. The pot and its contents are placed inside
the inner container which protects the insulation
from the pot. It also protects the insulation from
any food spills and makes the RHC easy to keep
clean. The inner container shares the same needs
as the outer container, except it does not need the
handles, and has the following additional needs:

 ^ Low thermal mass  (draws little heat from the
   pot as it heats up)

 ^ A lid that is also insulating and has a tight fit

 ^ Protects the insulation from moisture and being
   compacted by the pot

 > Should fit the pot to minimize the air space
   around the pot

                                                                    Guide to Designing Retained Heat Cookers
In some RHCs there are no inner containers and the
pot is simply embedded in the insulation. This allows
the insulation to easily become soiled, thus becoming
a health hazard as well as reducing its desirability both
aesthetically and thermally.  If insulation is used in
this way, it should be replaced frequently.

Safety—The assembly of the outer and inner container
and the insulation should produce a unit that:

^ Does not easily tip over

^ Has carrying handles that do not come off

^ Is not flammable

^ Does not grow mold or mildew

^ Is easily cleanable

^ Is child-resistant

Types  of RHC Projects
The retained heat method of cooking can be used
for many types of projects.

^ By disseminating do-it-yourself information,
   families can construct their own  RHCs from
   locally available materials. However, each
   component of the RHC must be thoroughly
   understood and taught. The use of inappropriate
   materials can lead to mold and mildew growing
   in or on the RHC, creating health hazards.

^ RHC promoters can also assist in villages with
   RHC construction. By being a part of the
   construction project, a promoter can supply tools
   and materials that may be otherwise unavailable
   locally.  However, the promoter should try to use
   locally available tools and materials, if possible,
   so the project will be sustainable. This hands-
   on approach also creates trust in  the villages and
   allows the promoter to reinforce  construction
   training with use training and to teach recipes
   that are appropriate for the local area.

^ RHCs can also be built in factories.  Mass
   production allows for a wider choice of materials
   to be used and for tighter control of quality.
   Since there is a broader choice of materials,
   factory produced units will typically have higher
   performance characteristics. There is also the
   potential for wider distribution of units since
   they can be sold through hardware stores and
   other distribution channels.  In some cases, mass
   produced units may be less expensive.

The Design Process
There are several specific phases relating to the
design of an RHC. Each phase has a specific
objective. These include:

^ Research
   The objective of research is to determine what
   others have done and what the results were for
   these prior works.

^ Conceptual Design
   The concept for the design must be defined
   using all the parameters  discussed in the next

^ Prototyping and Laboratory Testing
   Once the project concept is well defined, prototypes
   are constructed in accordance with the concepts.
   The prototypes are typically tested in a laboratory
   environment. The goal of laboratory testing is to
   determine if the design meets the objectives and to
   establish performance specifications.  It is important
   to ensure that production  items do not deviate from
   the performance objectives and specifications that
   have been designed into the  product.

^ Field Testing
   This is the first real customer-based test of the
   design. Without exception, there will be things
   that the users will find that could be done better
   or new features that could be incorporated with
   minimum cost that would result in a better

^ Design Review
   Following a successful field test, there will be
   a need for a design review  and for changes to
   be made in order to incorporate what has been
   learrted during the field test.

^ Pilot Production
   At this phase, a limited number of production

Guide to Designing Retained Heat Cookers
   units will be constructed and distributed to actual
   customers and their feedback collected and evaluated.

 ^ Hard Production
   This is the scaling-up phase. It cannot be over
   emphasized that all aspects of the project must be
   scaled-up at the same time. It does not do any
   good to scale-up production if distribution or
   marketing lags behind.

Comparative  Examples
When starting an RHC design, it is helpful to compare
any new design with examples that have previously
produced good results.  Below are three examples
that can be used for comparisons. Note that all three
graphs show temperature data from a five-liter pot of
water. The local altitude of these tests was 800 feet.
After three hours in the RHC, each pot of water had a
temperature between 80-85°C. All were plotted with
a temperature analyzer (Pico TC-08).

Figure  1 shows a test
RHC made using
a wood basket for
the outer container.
The insulation is
four layers of a wool
blanket. There is no
Figure 1 - RHC made
with wood basket
 1=02:59:36 y=82.54
    'C — Channel 1
StlBiH 000
          00:30   01:00   01:30   02:00   02:30  03:00
inner container and the pot with 5 liters of water is
embedded in the insulation.

There is an insignificant loss in temperature as the
transfer is made from the stove to the RHC. Since
                    there is no inner container, some cooling results from
                    heat loss into the wool blanket. From a thermal
                    standpoint, this RHC could be expected to produce
                    good, but not excellent results.  However, in actual use
                    the wool would become soiled and require frequent
                    washing. Also, wet wool has a bad odor,  which would
                    be unacceptable to many cooks. While this is a good
                    example for comparing with newer designs, it would not
                    be recommended for field use.
                    Figure 2 shows an
                    RHC made with a
                    cardboard box for
                    the outer housing.  A
                    wooden box would
                    have produced similar
                    Figure 2 - RHC made
                    with a cardboard box
                        'C —  Channel 1
                                 0 SIB HI S3 63
                             00:30  01:00  01:30  02:00  02:30  03:00
results (results not shown).  The insulation is three
layers of three-quarter inch thick foam wallboard
insulation. There is no inner container and the pot
is placed in the open space provided by the layers
of insulation.  The lack of an inner container allows
any spilled foods to get between the insulation
layers where it would be hard to clean.  While the
thermal characteristics are fair,  it would not have a
very long life in practical field use.

The RHC being manufactured by HELPS
International is shown in Figure 3 (page 5). It
has been designed for commercial sales through
hardware stores and non-governmental organizations
(NGOs) for their community development
programs. It was designed to be produced in a
factory environment using production tooling.

                                                                    Guide to Designing Retained Heat Cookers
The thermal mass of
the inner container
slightly cools the
pot in the first three
minutes, but the
excellent insulation
Figure 3 - RHC
manufactured by
HELPS International
 Ij PI W Graph
 1=00:24:51 y-87.44
        00:30  01:00  01:30  03:00   02:30   03:00   03:30   04:00
makes up for the extra loss of an inner container.
After three hours, the 5 liters of water is above 87°C.
This could be expected to produce excellent results.
The durability of this RHC structure will withstand
extended field use.

Both the inner and outer containers are made of easy
to clean polyethylene. The use of plastic welding
techniques is used to produce a double walled, rigid
unit. The two-inch space between the two walls is
filled with Styrofoam beads.

Styrofoam beads were the best insulation tested
and were also the cheapest (a byproduct of another
product). Styrofoam is soft and requires that it be
protected with a housing inside and out. Testing
indicated that a round housing was superior to a
square one since the round pot would fit snugly
inside. To make it the best possible fit, a special
pot was designed and manufactured for this RHC
application. The pot is supplied with the RHC.  Also
it is suggested in training that a cloth be used around
the pot to fill the air space between the pot and the
inner container. A cloth was  used in the test that is
represented on this page. The inner container has a
lid that is also insulated and provides a good seal.
Design Instrumentation
A valuable tool in the design of an RHC is a
temperature analyzer that can continuously plot
the temperature loss of a known amount of boiling
water placed in the RHC.

The temperature curves in the graphs in this Guide
were produced with a Pico brand temperature
analyzer Model TC-08 with type K (Chromel/
Alumel) thermocouples. The Pico temperature
analyzer can simultaneously record and plot data
from eight type K thermocouples. It can be
used with any computer with a universal serial
bus (USB) interface.  More information on this
temperature analyzer can be found at www.

The specific thermocouple suggested for
use with the analyzer is a Pico SEOO Type K
thermocouple (exposed wire, PTFE insulated).
At time of publication, the Pico TC-08 analyzer
costs approximately $450 and the SEOO type K
thermocouple costs approximately $10 each. It is
desirable to have at least three thermocouples for
use with the analyzer. These three thermocouples
will typically record the temperature of the pot
contents, ambient temperature, and outside surface
of the RHC.

It is  important that the thermocouple measuring
the temperature of the contents of the  pot is
located in a consistent location and that it does
not contact the side of the pot. It is suggested that
a wire fixture (see Photo 1) be made to hold the
thermocouple tip about one inch above the bottom
of the pot and in the center.
                                                     Photo 1 - Thermocouple Support

Guide to Designing Retained Heat Cookers
The recommended Pico analyzer sampling rate
should be at least one sample per second to capture
the small but rapid change in temperature that
occurs as the pot is transferred to the RHC.

The Pico temperature analyzer also allows notes to
be attached to each graph. The notes are saved in
the same file as the graph  and serve as a permanent
record of what each graph represents.

The use of this analyzer or its equivalent in  the
design of a RHC cannot be over emphasized since
valuable design information can be interpreted
from the shape of the temperature curves.
RHC Performance Objectives
A simple way to compare the performance of two
or more designs, using only a thermometer, is to
place a pot containing 5 liters of boiling water
into the RHCs and evaluate their temperatures
after 3 hours. A good RHC will still have
a temperature of 80°C after 3 hours and an
excellent design will have a temperature greater
than 85°C.  Even if a design does not meet these
values, it will still produce a significant health
benefit (through reduced smoke), wood savings,
and will free the cook for other more productive

Much more  information can be obtained by
using the Pico temperature analyzer to plot the
temperature loss. The temperature curve will help
analyze not only the amount of heat loss, but will
also help isolate where the heat loss occurs.

There are several factors that contribute to RHC
performance. By analyzing the temperature curve
generated by the Pico temperature analyzer, the
contribution of each factor to the heat loss can be
determined. These factors include:

^ Boiling temperature at the altitude where
   the RHC is being tested. There is little that
   the designer can do about this other than to
   understand that it will vary with  the area of use
   and to test at altitudes that can be reasonably
   expected for use.
 ^ The cook's ability to rapidly transfer the pot to
   the RHC. It is also important that a lid is on
   the the pot before and during the time the pot
   is being transferred to the RHC. This keeps
   in as much steam and heat as possible. This,
   along with the local boiling temperature (which
   varies with altitude), determines the starting
   temperature of the pot when it is placed in the
   unit. This is an important training factor when
   the RHC is introduced.

 ^ The thermal mass of the material inside the
   RHC (i.e., this affects the amount of heat
   that is taken from the pot and its contents
   to heat the inside structure of the RHC that
   protects the insulation). This causes a loss of
   temperature as heat is transferred to the inside
   structure of the RHC.  This occurs rapidly at
   first and decreases as the inside structure heats
   up. This generally occurs in the first thirty
   minutes that the pot is  in the  RHC. The
   temperature decay for the pot contents will
   decrease rapidly during the period that the
   inside structure is consuming  heat from the
   pot (see curved line of graph figures). When
   the inside structure is heated,  the temperature
   curve will become near linear  (see straight line
   on graph figures).

 ^ Once the inside structure is heated, a gradual
   loss of temperature occurs as heat is transferred
   through the insulation to the environment. The
   quality of the insulation and seal of the RHC
   lid will determine the slope of the temperature
   loss curve. In order to determine the amount of
   heat loss that can be contributed to the seal of
   the RHC lid,  a second curve should be run with
   the pot placed in a sealed container (such as a
   large, heat-resistant "turkey bag" that has a twist
   tie) prior to placing it in the RHC to eliminate
   steam loss during the test. A poor seal can be a
   major factor in heat loss. This is not to suggest
   that the sealed container ("turkey bag") be a
   part of an operational RHC but is used only to
   evaluate the losses associated with a poor seal.

A continuous plot of the temperature will give the
designer more information than just measuring the
temperature after 3 hours.

                                                                    Guide to Designing Retained Heat Cookers
   PLW Graph
 1=01:49:07 y=99.008
    •C — Channel 1
                            Channel 2
        00:30 01:00  01:30  02:00  02:30 03:00 03:30
 Figure 4 - Typical RHC curve

 In Figure 4, the starting temperature of about
 98°C for the pot contents placed in the RHC was
 a function of the boiling point at the local altitude
 and the cook's ability to rapidly transfer the pot
 from the stove to the RHC.  During the first 15-
 20 minutes (the curved section of the line), the
 temperature decreased rapidly at first then slowed
 as the thermal mass of the material inside the RHC
 became heated. Once the thermal mass was heated,
 the more gradual decay (the straight linear section)
 was a function of the quality of the insulation and
 seal of the RHC. The RHC tested here could be
 expected to produce very good results since the
 temperature is at the high end of the 80-85°C
 range after 3 hours.
    0:00:01   0:30:01   1:00:01   1:30:01   2:00:01   2:30:01   3:00:01
                      Time in RHC
 Figure 5 - Comparison of various RHC properties
Figure 5 shows various internal materials and
insulations (e.g. wood basket, cardboard box).
Note that in the two lowest curves the yellow
unit (triangle line) has higher thermal mass
(its temperature drops faster at first) but better
insulation (as indicated by the slopes of the near
linear portion of the curves) than the light blue
curve (star line). This type of information can be a
valuable design tool and would be overlooked from
only evaluating the three-hour temperature.

Pre-boiling Considerations
In order for the RHC to be effective, the pot
must be left on the stove until the contents are at
boiling temperature throughout. Depending on
what is being cooked, the time can vary from a few
minutes to a half hour or longer.
        Figure 6 - Internal temperature lag of food in RHC

        In Figure 6, the blue curve (circle line) shows
        the temperature of the water in a pot as it goes
        from room temperature to boiling temperature.
        The red curve (square line) is a plot of the inside
        temperature of a medium sized potato being boiled
        in the pot. The green curve (triangle line) shows
        the internal temperature of a one-inch cube cut
        from a potato.

        In conclusion, the pot should not be removed
        from the stove as soon as the water starts to
        boil.  Instead, it should be left on the stove
        until the internal temperature of the food has
        reached boiling.  If the food is in large pieces, it is
        recommended to continue to boil the food at least
        10-15 minutes longer. Additional time should
        be added as required for variations of boiling
        temperature as a result of the local altitude.

        Furthermore,  this test also shows the savings in
        cooking time  by cutting the food into small parts
        prior to boiling.

Guide to Designing Retained Heat Cookers
Marketing and  Distribution
Product Introduction
The introduction of an RHC project should be well
thought out and tailored to the community and culture
in which the project will be implemented. However,
it can be expected that at first the communities will
be skeptical that an RHC will perform as stated. This
can best be overcome with demonstrations rather man
just with a verbal pitch or written data sheets. The
introduction can also benefit by working with an NGO
that is already well known and trusted in the village.

Also, within most villages there are cooks (usually
women) that are natural leaders that can be
first educated on the benefits of the RHC. By
demonstrating the RHC benefits to them, they can
in turn communicate the benefits to others.

Training and Support
User training is extremely important to the success
of an RHC project.  Even the best designed RHC
will yield poor results if the operator is not efficient in
getting the pot immediately into the RHC and getting
the  RHC lid in place, or, if the RHC is opened during
cooking, which will let the steam out and cold air in
the  unit. Typically a cook will open a cooking pot to
inspect progress and to stir the contents. The cook
should be trained that if for any reason the RHC is
opened, the pot should be placed back on the stove and
brought back to a boil and then replaced into the unit.

Many recipes need to be modified for cooking
in an RHC. Therefore, in any RHC project it is
highly recommended that local food preparation be
researched, recipes converted, and training provided that
incorporates the new cooking techniques (See Table 1
- Suggested Cooking Times for the HELPS International

The project should be supported with periodic visits
to make sure that the cooks understand the use of
the RHC, and they are using it in an appropriate
way. Many times the cooks will find other beneficial
ways to use the RHC that had not been thought
of previously.  These should be documented and
included in future training and support.
Table 1 - Suggested Cooking Time for HELPS
International RHC
   Type of    Time to boil
    food      on stove
  Time in
retained heat
Total time
Beef stew
1 hour,
30 minutes
20 minutes
1 hour,
10 minutes
10 minutes
8 minutes
5 minutes
3 hours
35 minutes
50 minutes
30 minutes
25 minutes
20 minutes
4 hours,
30 minutes
55 minutes
2 hours
40 minutes
33 minutes
25 minutes
Awareness Building

In rural villages, information is often distributed by:

> Radio
   In many rural villages the radio is the main way that
   outside information is introduced to the village.
   Many of the villagers do have radios and listen not
   only for entertainment, but to receive announcements
   of personal and public types of information.

> Village to Village
   There is typically a strong flow of information
   from nearby villages. A successful project in one
   village will influence its introduction and success
   in nearby villages. Likewise, an unsuccessful
   project will be well known in nearby villages.

* Local NGOs
   In most rural villages there are already NGOs
   that have been working with the villagers
   for many years and have established trust.
   Members of these NGOs, if educated on the
   benefits of the RHC, can be excellent channels
   for awareness within the villages. In order to
   educate the NGOs in an efficient manner,
   seminars with many NGOs can be held and
   demonstrations given. Once these NGOs know
   and understand the benefits, they can influence
   many villages in a very effective way.

                                                                Guide to Designing Retained Heat Cookers

Testimonials From the Field on  the  ONIL Cooker

HELPS engineer Miguel Granados received the following comments during his follow up visits to three
villages that had field-tested RHC projects. These comments have been translated from Spanish.

On our first visits to Santa Avelina, Santo Domingo Xenacoj and Brisas del Moca we found out that 50%
of the ladies grind their frijoles on a stone while the other 50% like to eat them whole in their broth. We
also heard the ladies speak enthusiastically about the ONIL Cooker, for example:

    Dona Ana Chamay, Santa Avelina, Quiche— "/ leave my frijoles all night in the ONIL Cooker
    and they are cooked just the way I like them in the morning."

    Miguel's comment—Dona Ana. reported that she starts cooking her frijoles in the evening and by 7 pm
    they are put in the ONIL Cooker after l'/2 hours on  the fire. She lets the frijoles finish cooking in the
    ONIL Cooker over night liberating time and firewood. In the morning the beans are cooked and ready
    to serve. She reported that normally it would take her 4 hours on the fire to cook the frijoles.

    Dona Susana Cordova, Santa Avelina,
    Quiche"! don't know if this ONIL
    Cooker is working,  I can't feel it getting
    hot on the outside like the one I had
    Miguel's comment— This was an
    important statement for our investigation
    because it proves that our new insulation
    material worked better. The new material
   permitted less heat to escape and made the
    ONIL Cooker more efficient.

    Dona Maria Juana Sanjaj Garcia, Santo
    Domingo Xenacoj, Sacatepequez—"The
    ONIL Cooker helps me a lot in my
    business of selling tortillas."
    Miguel's comment—Dona Maria used the RHC to store 240 tortillas to keep them hot and soft for 3
    hours, enough time to sell all the tortillas for a meal.  Previously, when Doiia Maria prepared tortillas to
    sell, she wasted firewood keeping the fire going in order to sell the tortillas hot.

    Dona Rosa Eustaquia Chile, Santo Domingo Xenacoj, Sacatepequez—"/ used to get up
    during the night and start a fire to prepare oatmeal for my baby; with the ONIL Cooker, I can
    keep  oatmeal hot to use all night."
    Miguel's comment—Dona Rosa used to have to get up at 1 AM to start her fire to cook an oatmeal
    drink for her baby. Now, with her ONIL Cooker, she is able to prepare the drink at 7 PM and have it
    ready to serve at any time up to 6:30 AM. This saves her time and she can get more sleep!
Santa Avelina, Cotzal, Quiche

Guide to Designing Retained Heat Cookers
                                                     Cooker in Santo Domingo Xenacoj,
    Dona Maria Dominga Tun Aquino, Santo
    Domingo Xenacoj, Sacatepequez— "By 11
    AM and we have finished preparing lunch. I
    now have time to do other things."
    Miguel's comment—This was a very nice
    experience because starting at 9 AM, Dona Maria
    was able to finish preparing lunch by 11 AM. She
    prepared corn for her tortillas, a vegetable soup and
    white rice, all using the ONIL Cooker. From 11
    AM on, the stove was hot and available for other
    uses if needed. She saved fire wood and time with
    the ONIL Cooker and had 1 ¥2 hours to do other
Dona Antonia, Rio Bravo, Suchitepequez—
"The coffee is still hot in the morning!"
Miguel's comment—Dona Tona has 5 children
to take care of, the oldest is 7years old. It is a
custom on the Guatemalan south coast to get up
very early to go to work, taking advantage of the
cooler morning temperatures.  Dona Tona would
get up early every day to light her wood stove to
boil water for her husband's coffee, but with the ONIL Cooker, she prepares the coffee the night before,
and when she gets up, the coffee is still 72°C, hot enough to burn your mouth.  This helped Dona Tona
sleep a bit more in the morning; the ONIL  Cooker liberated time.

                                              General opinion, Santo Domingo Xenacoj,
                                              Sacatepequez—"We all heat water [at night] for
                                              bathing in the mornings."
                                              Miguel's comment— This was the answer of all
                                              people questioned in Santo Domingo.  The ONIL
                                              Cooker helps them keep water warm overnight
                                              to have ready to use for their morning bath.  The
                                              mornings in Santo Domingo are cold and the tap
                                              water is very cold.

                                              The main conclusion of the field tests is that the
                                              ONIL Cookers saved fuel and/or time.  It was
                                              rewarding to see that the women used their creativity
                                              in using the ONIL Cooker in new ways to help them
                                              save time and fuel in their daily needs.
Receiving RHC in Brisas del Moca, Suchitepequez
                                                  Miguel Granados,

                                                  Guide to Designing Retained Heat Cookers


Indoor Air Pollution from Home
Cooking and Heating
Indoor air pollution causes significant health
problems for the nearly 3 billion people
worldwide that rely on traditional biomass
fuels for their cooking and heating needs.
Over the last 30 years, awareness of the
environmental and social costs of using
traditional fuels and stoves and knowledge
about how to reduce emissions from these
stoves has grown. Yet the improved stoves
currently available to poorer customers do
not always represent best practice or an
understanding  of design based on modern
engineering. The  knowledge required to
design cleaner burning stoves exists in
centers of excellence in several locations
around the world. Providing this information
to those involved in promoting improved
stoves is a necessary first step to reducing
indoor air pollution exposure for stove users.
                                    About the Partnership for Clean
                                    Indoor Air
                                    The Partnership for Clean Indoor Air
                                    was launched by the U.S. Environmental
                                    Protection Agency (EPA) and other leading
                                    partners at the World Summit on Sustainable
                                    Development in 2002 to improve health,
                                    livelihood, and quality of life by reducing
                                    exposure to indoor air pollution, primarily
                                    among women and children, from household
                                    energy use. Currently, over 130 organizations
                                    are working together to increase the use
                                    of clean, reliable, affordable, efficient,  and
                                    safe home cooking and heating practices
                                    that reduce people's exposure to indoor air
                                    pollution in developing countries. For more
                                    information, or to join the Partnership, visit

             United States
             Environmental Protection

Office of Air &. Radiation   EPA-402-K-06-004
(6609J)              July 2007