• Transitioning to carbon neutral electric generation would replace a big climate problem in the U.S., since about 60% of its electricity comes from burning natural gas. 
  • The World Energy Forum forecasts that around 40% of electricity could be from wind and solar doing most of the heavy lifting by 2040, enabling a net zero global future. 
  • Today hydropower provides about 16% of the world’s electricity, generating power in all but two U.S. states. 80% to 90% of our electricity at the lab comes from the wonderful Columbia River.
  • ARC is working to clean up combustion so renewable biomass (domestic switch grass, for example) could cook food and heat homes when fossil fuels are no longer available.
  • Reading a book at night in a warm house is a wonderful thing. Somebody is playing the piano… Dinner was great.
(R. Crumb)

If renewable switch grass, for example, was burned cleanly enough biomass could join solar, wind, hydro, and thermal energy as sustainable energy replacements in the post fossil fuel era. ARC estimates that an emissions rate of 0.3 grams/hour of PM2.5 would protect air quality in cities and meet the Paris Agreements when replacing natural gas.

Not all that hard to do…

 “Earth is likely to cross a critical threshold for global warming within the next decade, and nations will need to make an immediate and drastic shift away from fossil fuels to prevent the planet from overheating dangerously beyond that level, according to a recent report from the Intergovernmental Panel on Climate Change.

… It says that global average temperatures are estimated to rise 1.5 degrees Celsius (2.7 degrees Fahrenheit) above preindustrial levels sometime around ‘the first half of the 2030s,’ as humans continue to burn coal, oil and natural gas.

…Under the 2015 Paris climate agreement, virtually every nation agreed to ‘pursue efforts’ to hold global warming to 1.5 degrees Celsius. Beyond that point, scientists say, the impacts of catastrophic heat waves, flooding, drought, crop failures and species extinction become significantly harder for humanity to handle.” Brad Plumer reporting in the New York Times, 4/21/23

On the other hand, transitioning to renewability accomplishes an almost universal dream of humanity.


Since 1976, ARC has been investigating how to improve heat transfer and combustion efficiency in Low Middle Income Countries’ wood burning cook stoves. Emissions of Particulate Matter have been shown to kill millions of people annually. PM concentrations are frighteningly high in homes without chimneys but emissions into outdoor air are an increasing health/climate concern. Incomplete combustion in cooking and heating stoves is an obvious problem especially when compared to the very clean combustion in more mature technologies like automobiles. 

The EPA biomass heating standard allowing two grams per hour of PM to pollute the environment is very lenient. National standards in Europe also allow biomass stoves to endanger health/climate. Cook stoves are forced to burn much more cleanly by stricter WHO standards and ISO benchmarks.

The Guardian’s Environment Editor Damian Carrington reported in 2021, “Despite their severe impacts on air pollution and human health, domestic heating emissions are under-regulated in the EU, especially when compared to other sources such as traffic. Neither the EU EcoDesign requirements nor the more ambitious Nordic ecolabel succeed to keep particle emissions from new stoves within acceptable levels. In 2022 a new EcoDesign stove will be allowed to emit 60 times as much particulate matter as an old truck from 2006, and 750 times as much as a newer truck from 2014.”

Total Plants: 107Metric tons/year:11,188,200
The pellets are used for fuel.

Depending on the size of the home, winter heating with a pellet burning stove uses from 2 to 6 tons of wood pellets per year. If the average house burned 3 tons per year, 3,729,400 homes could be heated with pellets currently manufactured in the USA. There are 142,153,010 residences in the USA. biomassmagazine.com/plants/listplants/pellet/US/

Bill Gates has written that the climate crisis can be solved by developing least cost, renewable technologies to replace fossil fuels. (“How to Avoid a Climate Crisis”, 2021)     

How do fuel costs compare?

Fuel Oil #2       Cost per million BTU = $30.19

Electricity         Cost per million BTU = $35.17

Natural Gas      Cost per million BTU = $15.38

Wood Pellets   Cost per million BTU = $19.15

LPG/Propane   Cost per million BTU = $41.13


Fuel switching from natural gas to renewably harvested wood pellets or split logs or dried wood chips (only if they can be burned cleanly enough to meet the Paris Agreements) seems to include a relatively small Green Premium. Replacing LPG/Propane, electricity, and Fuel Oil #2 with wood pellets seems like a good deal. 

sticks burning in rocket stove
The Jet-Flame pushes jets of primary air into the fire to aid combustion.
  1. When a wooden stick is burned a lot of smoke is produced but the made charcoal at the tip of the wooden stick does not make much smoke.
    Rocket Stove: Push the sticks in slowly so the charcoal at the tip is burning.
    TLUD: Charcoal covers the slowly burning fresh wood.
  2. If the stove begins smoking, the solid wood is being turned into gas too quickly, too much wood gas is being produced and un-combusted fuel is escaping.
    Rocket Stove: Pull the sticks back until just the tips are burning.
    TLUD: Reduce the primary air.
  3. Mixing the smoke, gases, flame, and air reduces emissions.
    Rocket Stove and TLUD: Cut up the laminar flames with static mixing devices or jets of primary or secondary air. Aim the jets of secondary air into the flame and adjust the velocity of the jets to completely cover the burning fuel. Primary air jets can also achieve close to complete combustion. Excess velocity in primary or secondary jets is detrimental when it reduces the combustion temperature.
  4. For close to complete combustion the temperature in the combustion zone needs to be 850C or above. The woodgas and air and flame have to be thoroughly mixed. The residence time needs to be 0.2 seconds or more. Reduce the amount of woodgas entering the combustion zone until close to complete combustion is achieved. Biomass fuels with 15% or lower moisture content are easier to burn.
  5. It is necessary to tune the stove under an emissions hood to achieve close to complete combustion. Change one variable at a time and test until significance is achieved.

The ARC lab is located in the Oregon woods where “hippies” and “rednecks” live on small farms in approximately equal numbers and share numerous points of view. I learned about these overlapping values when I accompanied my Dad, a Christian community organizer, to pot-luck meetings at nearby Granges, members of a farmers’ association organized in 1867. The one hundred and sixty two Granges in Oregon sponsor social activities, community services, and political lobbying.

My Dad was taught community organizing by Saul Alinsky in Chicago. He reminded his students to “Never go outside the expertise of your people.” https://www.goodreads.com/book/show/102748.Rules_for_Radicals  The people who have a problem have to be the ones to generate the solution. Mahatma Gandhi and E.F. Schumacher agreed. I watched my Dad as he listened and I admired his ability to help folks become aware that their constituency was a rainbow coalition.

Americans are a rich people but we often feel that life in the USA is getting worse and that this trend is out of control. Both “hippies” and “rednecks” can feel that nature is not being respected, that God has been forgotten, and that fighting for more money – being selfish – is largely responsible for the downward spiral. When many sorts of rural Oregonians visit our lab, they are happy that we are working to make renewably harvested biomass burn without making smoke.

Improving technologies can become a middle path that wins a rainbow coalition of friends.

Chart comparing energy output of 1 acre of grain vs 1 acre woodlot

The direct burning of biomass seems to be dramatically more efficient compared to ethanol for applications such as home heating, cooking, heating water, or drying clothes. It makes sense that not having to create alcohol from biomass would save energy. When the use of natural gas is decreased (due to climate change), burning biomass for heating seems like a fuel-efficient option that could reduce the extra burdens on electricity. 

One of my favorite reference books is “The Energy Primer” published in 1974. It has comprehensive review articles on solar, wind, water, and biomass energy. The following chart comes from a great article on biomass written by Richard Merrill. It shows that when renewable biomass is combusted, the efficiencies are much higher compared to making alcohol from biomass and then burning it.

The very clean burning of biomass allows efficient heating applications.

Chart comparing energy output of 1 acre of grain vs 1 acre woodlot
Smokestacks belch out smoke, spelling out CO2 in a blue sky. A Euro symbol floats to the right.
Smokestacks belch out smoke, spelling out CO2 in a blue sky. A Euro symbol floats to the right.
Image by Petra Wessman via Flickr

How can smoke, extremely dangerous for health and climate change, be ignored in carbon credit equations? Carbon dioxide and methane are counted but not smoke. Carbon dioxide is reduced when heat transfer is improved resulting in less wood being burned. Wood doesn’t make appreciable amounts of methane. 

Because smoke is not counted to earn carbon credits, smoky stoves with good heat transfer efficiency make as much money as clean burning stoves even though the Black Carbon in smoke is something like 680 times worse than CO2 by weight for warming. Because smoke is not included in climate credit math, adding clean burning to biomass cook stoves usually has to be as inexpensive as possible.

We know that adding high pressure mixing to Rocket stoves dramatically reduces smoke. As of 2022, forced draft is required to achieve adequate amounts of mixing. Mixing requires high pressures that (so far) cannot be made with natural draft. We know how to improve the Rocket but are in the process of completing the transformation to clean burning.

Nice to know the solution!

In 2021, ASAT (the for profit arm of ARC) won the Small Business Administration’s Tibbetts Award for work funded by their Small Business Innovation Research (SBIR) program, awarded through the U.S. Environmental Protection Agency (EPA). ASAT Inc. staff pose with their Tibbetts Award: Sam Bentson, David Evitt, Jill Allen, Dean Still, Kim Still, and Dr. Nordica MacCarty.

The investigation of how to reduce emissions and fuel use in biomass stoves continued with support from an EPA SBIR award. Two products were manufactured by our Chinese partner SSM, a heating/cooking stove and the Jet-Flame, a $12 insert that has made stoves 67% cleaner burning in field tests. https://www.jet-flame.com/

The Gates funded Global Health Labs (Dr. Daniel Lieberman) also worked with ARC/ASAT and BURN (Peter Scott) to improve the Rocket stove. BURN and ARC/ASAT added fan driven mixing to the Rocket stove.

Learning how to optimize the use of high pressure jets of air at high, medium, and low power required hundreds of experiments. Different pressures are needed as firepower is adjusted. The size of the fuel also affects emission rates. Experiments under the LEMS hood determine the location of jets, pressure, and volume of air for varying applications.

Dr. Samuel Baldwin

In 2011, Dr. Samuel Baldwin at the Department of Energy (who wrote the Bible on cook stoves in 1987) organized a two-day 100 person conference to identify how cook stoves could be improved and manufactured. Key recommendations were:

  •  At least 90% emissions reduction and 50% fuel savings are appropriate initial targets for biomass cook stoves. 
  • Multiple stove designs will be needed to accommodate a variety of cooking practices, fuels, and levels of affordability.
  • Technical R&D should guide and be guided by field research, health, social science, and implementation programs. At every stage, laboratory and fieldwork should be integrated into an iterative cycle of feedback and improvement.
  •  The cost and performance tradeoffs associated with the use of processed versus unprocessed fuels should be explored. While processed fuels can improve stove emissions and efficiency, the processing adds additional costs and these fuels may require a fuel distribution system.

From 2013-2015, ARC received a grant from DOE and spent three years establishing a baseline of stoves in use and then improved five types of stove prototypes with the iterative development process using the LEMS emission hood. The lab testing showed how combustion and heat transfer could be improved in those five types of stoves with the hope that field testing would evolve useful products that use less fuel and make less smoke. A book was written: Clean Burning Biomass Cookstoves, (2015) available on the publications page. The book was updated in 2021.