Dr. Paul Anderson shows a concentrator ring on a TLUD

The Concentrator Ring in a TLUD

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Dr. Paul Anderson shows a concentrator ring on a TLUD

Image from Dr. Paul Anderson’s Introduction to TChar (TLUD) Stoves for Haiti

The size of the hole in the middle of the flat plate, usually round, that seals the top of the combustor in a TLUD stove has important functions. The flat plate forces air jets/flame to travel horizontally in an attempt to completely cover the fuel bed. The diameter of the round hole has a dramatic effect on firepower. When it is too small, the fire can even be extinguished.

As with other variables, iterating changes in a prototype under the emissions hood can determine the compromise that best meets project goals. Larger holes in the concentrator result in higher firepower but can also increase emissions. In a 5” in diameter stove, a 3” hole in the middle of the concentrator is commonplace.

A StoveTec Fire Fly Lantern burns with a single column of flame

In the StoveTec FireFly lantern, developed at ARC, a small hole in the concentrator ring (1.5”) forces the flame into a narrow, vertical cylinder used for illumination. While the firepower is very low, so are the health-affecting emissions per minute.

Supporting Best Practice

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Three stone fire 3

Cooking outdoors, making hot fires, burning the tips of sticks to use less wood and breathe less smoke (photo: Clean Cooking Alliance)

In 2003, Aprovecho was hired by The Shell Foundation to develop a Rocket stove in Southern India. We found a wonderful co-op of potters that was selling two-pot burnished $4 ceramic stoves with chimneys. They sold 250,000 stoves per year. Mahatma Gandhi promoted this kind of stove in 1934. The ARC staff thought that, while trying to introduce a new concept like a Rocket stove, helping the potters to update their facility and perhaps tweak the design might result in this established manufacturer with an existing market and distribution system becoming more successful. It was great to work with and learn from so many, highly motivated local folks!

Appropriate Technologists are encouraged to first survey technologies developed in the project area. ARC looked around lots of villages to try to find out what expert cooks were doing to use less wood and breathe less smoke. We were trying to find out what existing factories were making innovations, and which established markets and distributors were selling products. One constant was that almost every distributor said that stoves had to cost less than $5.

Appropriate Technologists read in textbooks that learning from local solutions is best practice. Hundreds of Indian women transformed the Rocket into a useful stove. ARC did not know so much information was needed to be successful! We had to learn from experts and try to get out of our own way (as Alan Watts titled his autobiography).

Cover image of The Winiarski Wood Fired Agricultural Food Dryer

Winiarski: Improving Agricultural Food Dryers

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Cover image of The Winiarski Wood Fired Agricultural Food Dryer

Sometimes it’s too cloudy for solar drying and a wood-fired dehydrator can help with large scale food preservation. In 2002, Dr. Larry Winiarsk helped farmers in the wet mountainous region of Nicaragua to design and build a prototype wood fired dryer for cacao beans. The ARC publication “The Winiarski Wood Fired Agricultural Food Dryer,” details construction of a rocket-style wood-fired dehydrator.

It’s estimated that the optimal temperature for drying is between 120 and 130 degrees F. Sustained temperatures over 130 degrees can begin to cook the food. (When starting to dry foods it can be most efficient to go up to 150 to 160 F. in the initial stages of drying when lots of moisture will be evaporating out of the food.) 

A successful food dehydrator sustains these temperatures in dry air passing through food at a constant rate with even distribution for a variable period of time, depending on the food being dried. 1.) Hot air temperatures increase the rate of evaporation. 2.) Air flow through the food is equally important.

WHY?

Efficient drying moves the water inside the food into the surrounding air. Wet air cannot absorb more moisture. Hot, dry air picks up the moisture and air flow created by draft replaces moist air with dry air. In a Winiarski food dryer, air is efficiently heated and sufficient airflow of dry air through the food increases the rate of dehydration.  

The food dryer features: a) burning biomass heating air b) is relatively air tight, c) has a large chimney or fan that removes moist air and moves dry air through the food. A large chimney usually creates the draft necessary for sufficient air flow.

Emission testing equipment set up at an Oregon home

What’s Cooking at Aprovecho

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The LEMS in Ethiopia

Jaden and the trainees in the Ethiopia lab

In March, Jaden traveled to Ethiopia to assist in the installation of the LEMS and train lab technicians on ISO testing for cookstoves.

15 trainees from all over the country attended the training. The LEMS was procured by SNV and their sponsors and was given to Ethiopia’s Department of Water and Rural Energy at the end of the training and installation.

The installation of LEMS in different countries is vital in creating clean cooking solutions that can be used throughout the world. We hope to continue working with the lab in Ethiopia to design new stoves.

Proyecto Mirador in the Lab

Proyecto Mirador testing their stove in their lab in Honduras

Proyecto Mirador has been working on improving the efficiency of their Dos por Tres stove. After successful tests in their lab, they traveled to Aprovecho from Honduras to confirm their results.

They got the same results in both labs, showing how effective iterative design testing with the LEMS can be. Now they can install stoves that use less fuel and cook things faster in Honduras and Guatemala.

Field Testing Results Published

Emission testing equipment set up at an Oregon home

In 2023, we measured the emissions from cordwood heaters in Oregon. There are very few studies that evaluate emission measurements in the field for wood heaters. As seen from our experience in cooking stoves, emissions in the field are often higher than lab tests, and field studies help us understand how people use their stoves so we can make better designs.

We’ve been using the data we collected to create lab tests that reflect user behavior and design clean and efficient heating stoves that meet user specifications.

The resulting paper, In-situ Measurements of Emissions and Fuel Loading of Non-catalytic Cordwood Stoves in Rural Oregon, was recently published in the Journal of the Air & Waste Management Association.

Market Driven Stoves

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Photo by Güldem Üstün on Flickr

One of the biggest mistakes I have made was thinking that I could predict what stove would sell in a market. If only I had always followed Sam Baldwin’s advice and done market testing before manufacturing! In Southern India, as part of the 2003-6 Shell Foundation project, we had outspoken distributors who yelled in meetings that a successful stove had to cost $5, that 5,000 had to fit on a truck, and that it had to be designed by cooks! The stove had to be short so food could be stirred and work well at the low firepower required by villagers around Chennai, toast a chapatti, etc., etc.

When the carbon market crashes, affordable stoves continue to be sold and used. When stoves are purchased the consumer is convinced of their utility. The trick is to try to bring best solutions into marketable products but, luckily, engineers love a challenge!

A pot skirt, SuperPot, constant cross sectional stove top, stick support, keeping a fire hot, can all significantly increase heat transfer efficiency. Even Jet-Flames can be made for around $5. TLUDs can be inexpensive. There are many techniques to improve the market driven stove! 

Check out the new Osprey funded book Improving Biomass Stoves, 2025  for examples?

Fireless Cooking Has A Long History

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Thanks to Robert Fairchild for sending this reminder that what we call a “Haybox” cooker has a lot of history behind it!

Of course fireless cooking methods have been used since ancient times, but fireless cookers began to be introduced to U.S. in the mid 1800s, becoming commercially manufactured and quite popular in the US in the early 20th century. The Haybox, or “retained heat cooker,” works by placing a boiling pot of food into a well insulated box that keeps the heat in the pot, generally producing thoroughly cooked food in a couple of hours without further interventions from the cook.

Retained heat cooking can save 20%-80% of fuel for cooking, depending on the food and amount cooked. This method is not safe for every kind of food, but Aprovecho cooks especially love it for a big pot of beans or rice. The fire and the pot don’t need to be tended after boiling, and the food never burns!

If you are interested in making one for your own use, here is the ARC Rule of Thumb Design Principles for a Haybox.

You can find an excellent, well illustrated history of the Fireless Cooker, from early versions through its modern re-emergence in low-income countries, at the USDA National Agricultural Library: The Fireless Cooker (Emily Marsh, Ph.D, MLS)

Remembering Ken Goyer

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https://paulneevel.com/hp_archive/pix/kengoyer.jpg

On the front porch of the house he built in West Eugene, Ken Goyer shows an example of the Six Brick Rocket Stove

Photo by Paul Neevel for the Eugene Weekly

I think about Ken making the lightweight, insulated bricks from Bailey Hill yellow clay for the Uganda submerged double pot stove in 2002. Exposing the sides as well as the bottom of the pot(s) to flame and hot gases increased fuel efficiency. The Rocket combustion chamber, also made from Ken’s recipe (clay and sawdust) was a 5” in diameter, 12″ high cylinder, placed under the first, larger pot. 

We tested the stove using one pound of wood. 6.6 pounds of water in the first pot (12″ diameter) boiled in ten minutes. We had a great week of sunny, windy weather and it was great fun to work with Ken and Peter Scott (Burn Stoves), who was about to go to South Africa. 

I met Ken when he was doing “Ken’s Ten-Buck Tune-Ups.” He first saw open cooking fires when he went to El Salvador in 1992 to help Sylvia Gregory with her women’s empowerment project. With funding from Rotary Club, Ken directed construction of brickmaking kilns for refugee camps near Lira in Uganda and Gulu in Darfur. He helped to start Aid Africa and is one of the inspirational people we miss and so fondly remember. He was one of Larry Winiarski’s best friends.

New on the Website! Improving Biomass Stoves, 2025

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The new Osprey funded book is a compilation of fifty-one updated newsletters, reflecting the current state of knowledge at ARC. 

Stove experiments fail to improve prototypes as often as they succeed. One of the great things about iterative development (testing effects of single changes in prototypes under the emission hood) is that you learn as much from failures as from success! Every day moves us forward. 

How to achieve close to complete combustion and close to optimal heat transfer efficiency are describable in single page summaries. 

Aprovecho is helping to manufacture biomass cooking and heating stoves that are clean burning enough to protect urban air quality and meet the Paris Agreement. Most of the stoves that we help to make are not this clean burning, but how to achieve cleaner combustion is better understood and less expensive to achieve.

The hope is that these short summaries will be more accessible and more fun to read compared to previous longer-winded attempts at communication.

Our lab is open to visitors and we try to be good hosts. After years of trying, the coffee is becoming more palatable. 

Come on by!

Aprovecho Research Center, 2025

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ARC started in 1976, almost 50 years ago. 

In 1982, the original cook stove consultants returned from global travels to Oregon, bought 40 acres of forested land at the end of a road, planted a garden and started talking to Dr. Larry Winiarski, (Oregon State University) learning how to improve combustion and heat transfer efficiency. 

Dr. Nordica MacCarty, an associate professor at OSU, is the Executive Director of ARC and continues investigations of how wood fires can better help humanity. She has worked at ARC off and on for 25 years. Rigorous science-based experimentation, field learning, publication of peer reviewed journal articles and market-based manufacturing and distribution intertwine as ARC matures.

Learning from experience, eating a thousand kinds of food, succeeding now and then, is always great!

Building Blocks to Health

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In 2018, the World Health Organization published the book “Air pollution and child health: prescribing clean air”. The report concludes, “Every day around the world, billions of children are exposed to unsafe levels of air pollution. The result is a global public health emergency.” 

The WHO suggested “prescriptions” to clean the air and protect health:

  1. Use clean household energy for cooking, heating, and lighting.
  2. While waiting for clean to be available, use technologies and fuels that reduce exposure such as low-emission biomass cook stoves.
  3. Minimize the time children spend around smoky fires.
  4. Increase ventilation or install a chimney.

A combination of interventions is usually most cost effective. 

ONE

  • Help to make clean burning stoves available.
  • Promote solar lighting.

TWO

  • Forced draft stoves can burn up a lot of the smoke.
  • An adjustable Pot Skirt forces the hot gases to scrape against the sides of the pot as well as the bottom reducing fuel use by about one-third. That results in one-third fewer emissions!
  • A light weight, abrasion resistant Rocket combustion chamber can burn up ~ 50% of smoke compared to the open fire. 
  • Winiarski designed stovetops can increase heat transfer efficiency by ~8%.

THREE

  • Promote reduction of exposure to family members, especially to women and children. 

FOUR

  • Doubling the air change rate reduces smoke in half.
  • Locate the fire under a window on the low pressure side of the house.
  • Cook outside.
  • Chimneys have been a part of traditional houses for centuries.
  • Cook with a chimney!