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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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!

Applications of Pulling Woodgas Through Burning Charcoal

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We experimented at SSM with a “Horizontal TLUD”

As seen above, the draft of a Rocket stove can pull woodgas horizontally through made charcoal. The tips of the sticks turn into hot charcoal.

Secondary air is pre-heated in the circular annulus before entering the fire in front (or above) of the made charcoal, as in a TLUD.

Primary air is adjusted by covering the fuel entrance. More air makes a bigger fire.

PM2.5 is dramatically reduced when conditions are well adjusted under the emissions hood: (850C for 0.2 seconds, etc.)

Recently, we have been trying the same approach in pellet and log burning biomass heating stoves.

It is so interesting to switch back and forth between heating and cooking stoves.

Solvable problems make life great!

Green sign reading Sure, Light Up

Wow! The clean biomass future is now!

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Central Boiler combustion chamber

Last week Dean and Travis went to the Hearth, Patio & Barbeque Association Expo in New Orleans to get updated on the latest heating stove technologies and to meet and talk to stove companies. Three days was a short time but we made many friends and learned a lot!

The CENTRAL BOILER outdoor log and pellet furnaces stood out as one of the newest innovations. It can be imagined that in a sustainable biomass future, heating big buildings (even high-rise apartments?) with logs or pellets might be as useful as freestanding stoves heating rooms. The same (bigger/smaller) clean burning combustion systems deliver renewable, home-grown heat to occupants in bigger/smaller buildings. Maybe pellets could be poured down the same delivery chutes that are used for heating oil in New York City buildings?

Admiring the automated house-sized furnaces on display at the Expo made the possibilities seem so much better defined. 

See: centralboiler.com

Wood Heating: Heating Design Load

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Burning wood slowly (and cleanly) can be a big part of the challenge when improving heating stoves. Air tight, insulated houses do not need big fires to stay warm. If the fire is too large, the house gets hot and folks are opening windows!

What firepower is needed to keep a house warm but not overheated?

“If you build a small, tight, well-insulated home — in other words, a green home — it won’t need much heat. Since typical residential furnaces and boilers are rated at 40,000 to 80,000 BTUH, they are seriously oversized for a super-insulated home, which may have a heating design load as low as 10,000 to 15,000 BTUH.” www.greenbuildingadvisor.com/article/heating-a-tight-well-insulated-house

15 thousand BTUs per hour is equal to about 4.4 kilowatts. (Burning ~2 pounds of dry wood per hour in a stove with a good heat exchanger.)

The required firepower of the heating stove is dependent on the losses from your house. Old-fashioned houses can require big fires to replace constantly lost heat. 

The Green Building Advisor says that it is most cost effective to reduce the air leaks first and then increase the amount of insulation in a home. 

Matching needed firepower to your heating design load should factor into your decision of what stove to buy. It is not difficult to do an energy audit of your home.

www.energy.gov/energysaver/home-energy-assessments