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Burn wet waste fuels super-clean, super-efficient !

Over 42 years of Research and Development in the field of biomass energy have produced 14 prototypes of possibly the most efficient and clean-burning waste-fueled furnaces in the world.  Some of these prototypes, all of them with personal names, are shown below.

Helen - 1500F combustion ~ 1985

“Helen” 7,000 - 50,000 Btu/hr cookstove/air-heater with condensing heat-exchanger, weight 376 lb. Built 1985.  Note hand on stovepipe while combustion is 1500F Tested by DOE/Bonneville Power

vaagner castings

Vaagner’s all-ceramic interior shell, showing fuel hopper, gasification zone (without hearth grates) and combustion chamber.


“Gertrude” 80,000 Btu/hr Sawdust-fueled furnace with condensing heat-exchanger heats air and water. Integrated with solar heating of water, house, greenhouse.

godzilla castings1

800,000Btu/hr “Godzilla’s”
all-ceramic interior. 
Note hollow SiC ash-dumping
grate rungs at gasifier hearth.

Flame through rear window02

Glowing top of combustion chamber viewed over heat exchanger.  Note glowing thermocouple and gas probe on Right.  Combustion temperatures as high as 2500F were achieved in tests for Stirling engine efficiencies.


< Chick drawing showing the various integrated components.

Combustion through port-sawdust trimmings-1

View through lower view port (pictured in photo at right) showing clear hot gas being liberated from sawdust fuel

Stump Burner

30ft tall brush and stump gasifier under construction.  It will produce electric power from steam and charcoal for soil enhancement.

6-page PDF summary of waste energy technology


“Vaagner” 12,000 - 175,000 Btu/hr hot air furnace, fueled with chips, sawdust, refuse-derived-fuel-pellets, etc. .  Note yellow computer/damper motor control center using oxygen sensor & thermocouple inputs

“Chick” 800,000Btu/hr fully automated
multi-fueled hot air furnace
pictured here under construction with designer/builder, Larry Dobson standing
in gasifier hopper

Chick from Control Side

Opto-22 Factory Floor computer control system for monitoring, analyzing and developing control algorithms

^  Chick during initial fire-up. Note bucket of condensed water near base of flue. This test burning stringy green chips condensed gallons of water per hour operating on natural convection flow without electricity at over 90% overall system efficiency.
Exhaust had no smell.

Chick side-labels

Diagram of Chick 800,000 Btu/hr hot air furnace with close-coupled,
mutually augmenting gasifier, combustor, heat exchanger.

HX-castings basic

The most recent “Roundy” 32Kwh household energy system design, showing the inside ceramic hopper/preheat/combustion shells, surrounded by a spiral water heat exchanger.  This is both a water heater and a gasifier for running an internal combustion engine or genset.

To learn more about this technology and download a complete set of plans ~ FREE ~ click here.

Woody-3 Castings with Springclamps02

This is a drawing of the internal ceramic shell of a stand-along cross-draft gasifier with gasification air preheat in the sealed shell surrounding the ceramic (not shown).

The castings are keyed into each other and kept from separating vertically by gravity and horizontally by the spring-clamps shown above.

Click Here for an in-depth report I wrote on
“Biomass Energy - State of the Technology, Present Obstacles & Future Potential”,
for the U.S. Department of Energy, Conservation and Renewable Energy,
Office of Energy Related Inventions, 1993

Learn here about the cleanest, most efficient furnace fueled by one of the most promising domestic alternative energy source available anywhere!



About 98% of the energy used by mankind today is derived from biomass; it is solar energy stored in plants by photosynthesis.  Although our most widely used fuel source is nonrenewable fossilized biomass (coal, oil, natural gas),  plants store over 60 times the total energy consumed by humanity annually.  The world's forests are being destroyed at an alarming rate, with tremendous  waste of valuable resources.  With prudent management and the increased use of marginal crop land for production, biomass can make a large and continuous contribution to our energy supplies.

The amount of unused biomass waste produced in the U.S. and Canada is staggering. There is a huge amount of cheap, usable energy available to us in the form of household and business waste, tree trimmings, sawdust, hogged fuel, demolition and land-clearing waste, logs, chunks, pellets, peat, Refuse Derived Fuel pellets, municipal wastes, low-grade waste paper and cardboard products, and all kinds of agricultural waste from corn cobs to rice hulls and bagasse. These resources are locally available in various forms everywhere, inexpensive and often free.

In our throw-away society, biomass waste is becoming an increasingly costly disposal problem.  Governmental agencies are clamping down on indiscriminate dumping and leaching from existing piles of wood & agricultural waste.  Slash burning from logging operations is being prohibited totally in more populated areas.  Landfills are filling faster and faster.   The US EPA's strict new regulations are costing $1 Million per acre to open new ones and have forced the closing of half of the nation's dumps.  Well over 1/3 of our Municipal Solid Waste (MSW) is biomass suitable for fuel, which could replace millions of  barrels of imported oil a year.   All fossil fuel prices are predicted to escalate at an increasing rate, while costs for biomass fuels are dropping as disposal costs rise.  Waste Biomass promises to be one of our greatest energy bargains for the foreseeable future.  Fuel sources are decentralized and are ideally suited for small commercial wood-waste furnaces to heat manufacturing and processing facilities, schools, hospitals, hotels, convention centers, greenhouses, etc. The energy can be used for processing heat, steam, hot water or the co-generation of electricity when coupled with a Stirling heat-engine generator (such as External Power’s opposed tandem linear Stirling alternators), a microturbine generator, or thermophotovoltaic collectors such as JX Crystals’.


Until now no one has manufactured a biomass/waste combustion system that was clean burning enough to pass strict new emission regulations and also affordable, automated, reliable and capable of burning the greatest variety of fuels.

Larry Dobson has spent 25 years solving five major problems in  biomass combustion technology:

  1. Burning the great variety of biomass fuel types, sizes, and moisture content available, all in the same system;
  2. Perfecting the combustion process for this wide spectrum of fuels to reduce exhaust emissions to well below the most stringent environmental regulations in the world;
  3. Increasing overall efficiencies of biomass energy from 65% to over 90%, even with wet fuels;
  4. Optimizing the fuel feed, combustion, heat exchange and ash removal into a compact, cost-effective, maintenance-free system that is automated and simple to operate;
  5. Addressing the needs of the major market:  small commercial applications, schools, institutions, conference centers, business complexes, rural communities, agricultural uses and a rapidly growing international market.

To date, waste combustion technology has only been cost-effective in large, complex and expensive 30-300 million Btu/hr. systems. They have been built mainly for the disposal of municipal waste and for processing heat and cogeneration in the lumber and paper industry.  No one until now has been able to meet the needs of the market for smaller commercial systems, which actually represents the greatest number and best uses for decentralized biomass energy applications.


Our quarter-century-long endeavor has yielded twelve prototype biomass energy systems and a patent on the design of the cleanest burning biomass combustor ever tested.

It is now possible to utilize large quantities of waste materials and biomass of all types, efficiently converting it into usable energy instead of burying it in costly landfills.

The most recent production prototype is an 800,000 Btu/hr commercial hot-air furnace fired by wood waste and other biomass fuels.  This was a joint project involving the US Department of Energy, the University of Arkansas, the Arkansas State Energy Office and the Foundation for Organic Resources Management to heat brooder houses at the U. of Arkansas poultry research department, burning chicken litter for fuel.  It incorporates automated fuel feed, a patented combustion system that preheats combustion air to 1000F in a multi-cavity refractory ceramic heat-exchanger, a highly efficient down-draft counter-flow heat-exchanger that condenses the moisture out of the exhaust, and automated programmable electronic controls.

Throughout the world there is a great need for clean conversion of waste to energy in small, decentralized community sites.  Existing systems are prohibitively expensive and unreliable.  Because our technology is so clean and simple and capable of handling such a diversity of fuels, it is ideally suited for such applications.

Energy users everywhere are looking for ways to cut costs, reduce waste, and comply with environmental regulations.  There is a large immediate market for this system in situations where biomass waste disposal is a priority or where the need exists for cheap hot air, hot water or steam.  When we consider the full, long term environmental costs of fossil fuels, we must look for alternative sources of energy.  Biomass is by far the largest contender today.



A prototype residential cookstove built by Dobson was officially tested in 1986 by Omni Environmental Laboratories for the U.S. Department of Energy/Bonneville Power, burning green sawdust of 44% moisture content, with no fans and no catalytic afterburner or stack cleanup of any kind.  Its particulate emissions were 65 times cleaner than the best woodstove at that time, several times cleaner than the best pellet burner, and considerably cleaner than the average oil furnace.

Flue gases were usually so cool that clear water was condensed out in the heat exchanger.  Carbon Monoxide emissions in the stack gases were 1/7500th of the Federal Auto Emissions standard, 1/100th of the gas industry's standard for "CO-free combustion," and 1/2 of the EPA's standard for acceptable 24 hour indoor air quality. Since this prototype, two improved versions have been built and tested with everything from household-, office- and greenhouse-waste to soggy bark and rubber.  In tests with a newer prototype burning RDF (Refuse-Derived-Fuel) pellets, excess air was brought down to less than 1%, while maintaining low carbon monoxide emissions (0.002%). This is unprecedented in biomass combustion.  Only large modern gas furnaces achieve such efficiencies.  The latest prototypes are even cleaner, consistently showing CO emissions undetectable on a 3000 ppm scale! Emissions contain no sulfur and are less acid than rainfall near many fossil-fueled industrial areas of the world.



Integrated System

All components of the system are designed to work together for efficiency, compactness, cost-effectiveness, durability, and maintenance-free operation.  Gas flow analysis is used to optimize all flow channels, taking into account changes in temperature, volume, viscosity, turbulence, friction, the unique constituents and properties of biomass gases, and the heat transfer properties of  the materials used in it's construction.  The whole is much greater than the sum of the parts.

Internal Ceramic Heat-Exchanger

Extremely strong, durable, fatigue & shock-resistant refractory ceramics are used in the combustion areas.  A complex of hollow channels and special silicon carbide heat exchangers transmits heat to the incoming combustion air.  Metals are not used in the combusion zone because metals, no matter how exotic, cannot endure the heat and corrosion in conditions of optimum pyrolysis/combustion.  High-temperature ceramic fiber insulation is used along with concentric heat-exchanger shells to move the heat where it is needed to optimize gasification and combustion, and to eliminating excessive heat that produces slag buildup and ceramic fatigue. 

The thermodynamic properties of these heat-exchangers increase natural draft and reduce the need for exhaust fans (and their tendency to send unburned embers, soot and ash to clog up the heat-exchanger and increase particulate emissions). The heat-exchanger is designed specifically for high-ash biomass fuels so there are no horizontal surfaces to collect fly ash.

All soot is burned in the combustion zone.  Any remaining fly-ash is removed from the exhaust stream through a combination of gravity precipitation and steam-condensation entrainment, which continuously scrubs the exhaust and lower heat-exchanger surfaces.

Highest Turn-Down Rate in the Industry

A 200,000 BTU/hr model can operate as low as 14,000 BTU/hr with 95% overall-efficiency and over 99.9% Combustion Efficiency.  The present prototype has a 25-to-one turn/down ratio. This allows the unit to operate at an "idle" while continuing to burn cleanly and efficiently, and always be ready to “turn on the coals” when heat is needed.

True Three Stage Gasifier/Combustor

Primary gasification and secondary combustion are separately controlled by a microprocessor.  No heat is taken away from the combustion process except to preheat the combustion air, increase the pyrolysis activity, and prevent melting and slagging up of the ash.  Even wet fuels with up to 2/3 their weight in water are dried and vaporized (pyrolysed) by the highly preheated incoming combustion air. The additional steam acts as a catalyst, improving mixing, speeding heat-transfer and shortening the flame path.


All aspects of combustion and fuel feed are monitored and controlled by a state-of-the-art computer.  This is especially important  with the ever-changing combustion conditions of biomass and waste fuels.  The microprocessor analyses data from various inputs such as switches, thermocouples, other temperature probes and an oxygen sensor to continually monitor exhaust and optimize air-to-fuel mixture, refuel and remove ash when needed, and signal when anything needs attention.  The ceramic interior is prevented from thermal shock through subtle control algorithms in the microprocessor programming and precise monitoring of the various temperature and position parameters.  The hot air systems will operate manually when the power is out, producing through natural convection flow hot air over 300F hotter than the cool exhaust temperatures.

Gravity Flow Fuel Feed

The system can take any size, shape and configuration of fuel up to 7” without hang-ups. Counterweighted hopper flaps prevent heat and smoke loss through upper hopper, signal status of fuel reserves, turn on fuel feed in automatic feed systems, and facilitate smoke-free loading of fuel.

The most recent prototype of these concepts is the “Roundy” hydronic furnace, which also functions as a stand-alone gasifier.  For more details and free plans, go to: 



Inventor/designer of the Northern Light family of biomass furnaces


From childhood Larry was fascinated with fire and carried out extensive seat-of-the-pants research in bombs and rockets.  After exploring work in research chemistry with Monsanto and other companies, Larry switched to Political Science, went off to India in the Peace Corps, and explored the fire within. He also worked in India at the Utar Pradesh biogas research center under Ram Bux Singh.  Eventually however, Larry continued private research into alternative energy applications; solar, wind, biogas, tidal, air, and integrated residential systems.  In 1977, Northern Light R&D was started by Dobson for the purpose of researching waste to energy systems, combustion technology, alternative energy, appropriate technology, and a variety of other systems relating to the recycling and utilization of the growing quantities of resources entering the waste streams.

Dobson’s recent work includes the development of a hot air furnace for heating poultry houses burning chicken litter.  This began as a joint project with the U.S. Department of Energy, the Arkansas Energy Office, the University of Arkansas, and the Foundation for Organic Resources Management.  The project was then funded by External Power, Athens OH, in conjunction with the development of a Linear Stirling Alternator for cogeneration of power and heat.

He is currently building the “Roundy” gasifier and looking for funding.


Dobson's expertise includes:

  • 38 years of research and development in the field
  • 3D Solid Modeling component design
  • Optimization of gas flow, temperature, heat transmission, throughput, fuel handling
  • Utilization of recent advancements in refractory materials, oxygen sensor and controls systems
  • Designing of integrated controls and coordinating software development
  • Development of new approaches to ceramic component design and manufacturing



  • Alternative Sources of Energy Magazine, grant, 1977
  • Washington State Energy Office, grant, 1987-88
  • Vaagen Timber Products Company, assistance in prototype development, 1988
  • US Department of Energy, Energy-Related Inventions Grant, 1989-1991
  • Pyro Industries, Burlington, WA – prototype testing, R&D of 1.5MMBtu condensing boiler 1992-95
  • US Department of Energy, Commercialization Ventures Program, 1998-2002
  • External Power, Athens, OH – R&D of Commercial biomass/waste-fueled cogeneration modules, funded in part by grant from the National Renewable Energy Laboratory’s “Small Modular Biopower Project” 2000-02
  • University of Minnesota's SE MN Regional Partnership Energy Project grant 2003


  • Proceedings of the Weltkongress Alternativen und Umwelt, Vienna, 1980, A High Efficiency Home Energy System Burning Biomass
  • Alternative Sources of Energy Magazine, 1980, The Grendle Report
  • The Mother Earth News Guide to Home Energy, 1980, An Amazingly Efficient Sawdust Stove
  • International Bio-Energy Directory and Handbook, 1984
  • Proceedings of the 1986 International Conference on Residential Wood Energy, High-Tech Non-catalytic Woodstove Design Considerations
  • Proceedings of the 1988 Washington Wood Utilization Conference, A State of the Art Woodchip Boiler
  • Biomass Energy - State of the Technology, Present Obstacles & Future Potential, U.S. Department of Energy, Conservation and Renewable Energy, Office of Energy Related Inventions, 1993
  • Proceedings of the Conference on Charting Our Energy Future, Pacific Energy Innovation Association, Vancouver, Canada, 11/2000