Q: How much does it cost to build a gasifier?

A: Using locally available parts you can start making gas for under $1500 in materials. See our Intro to Wood Gasification report for several budget scenarios.

Q: How much wood does it use?

A: Expect to use 2-3 pounds of wood for each kilowatt hour depending on engine size, type and speed. Expect about 2 pounds per mile driving.

Q: What size engine can I run?

A: This design is best for 1-5 liter engines. You can go a little smaller with bone dry wood or charcoal mixed in. There are sizing charts inside for larger engines (5+ liter), but you would need to scale things up a bit.

Q: Can I fuel any engine?

A: You can fuel just about any spark ignited engine with some modification for the different air fuel ratio. (We have a book on that) Diesel engines need at least 20% diesel to self ignite or they need spark conversion. Woodgas works in high octane situations beautifully. It’s effective octane is about 104 we hear.

Q: How long has this technology been around? Do lot’s of people use it?

A: The technology has been in active use for 150 + years. During WWII it powered over 1 million installations. It’s a major source of power in rural areas of developing countries. The technology gets forgotten every few decades, so Westerners are just rediscovering this amazing home grown energy source. The books we offer on wood gasification are meant to reinvigorate this knowledge and make sure it is never lost again.

Q: Do you sell these machines?

A: We don’t sell the machines except for the rare units we build for workshops. Our time is focused on creating a zero waste village concept that integrates this technology with solar, and other renewable energy technologies and getting that knowledge into books too.

Q: What size wood can I use? Do logs work?

A: The wood needs to break down fast enough to make gas for the engine. Logs are too dense and sawdust/mulch/bark is too small. Thick wood chips about the size of your thumb are best for small engines. Chunks the size of a small fist are best for large engines.

Q: How would you describe the process of gasification to a child?

A: I would compare the process to heating an ice cube. When it’s cold it’s solid, add heat and it becomes a liquid, add more heat and it becomes a gas. We heat wood in an oxygen starved environment and it shifts from a solid into a gas without burning up. That gas is made up of hydrogen, burnable carbon gases and inert nitrogen from the little air that does enter the system.

Q: What is the power density compared to petro fuels? Can I store it?

A: Power output is 50-65% generally because there is inert nitrogen in the gas stream. Users compensate by sizing up their engines or gensets. Example: 10kw propane yields 5 – 6.5kw on woodgas. You can store the gas in bags like a biogas. Some people compress it, but it doesn’t liquefy and it’s not recommended unless you work with compressed gases regularly.

Q: Is it safe?

A: It’s flammable gas, of course it’s safe;) If you are careful and use it in a well ventilated area with safety glasses and gloves you should be fine. Do not pump the gas into your home however because there is no scent added to warn you of a leak. Carbon monoxide is present, so use common sense.

Q: How do you recommend I integrate this with my homestead? Use schedule?

A: Fire up a batch run in the morning for a few hours to get things warmed/charged up while you use heavy loads. Use solar panels during the daytime when loads are low. Then at night run another batch of wood to fuel your generator and get things warm for the night ahead. Mount your system under a roof with at least one open wall or a big door. Keep it away from house windows. Preferably it is near a greenhouse or somewhere you can harvest waste heat to heat water for radiant heating. Heating water is an ideal source of heat because you can also use the sun and the heat from compost, so they all work together nicely.

What is the best way to learn?

Step #1 make gas. Just flare gas during hour long tests for a week and focus on getting dry wood at the right size into the machine. Step #2 connect the machine to an engine and get the air fuel mixture correct. Continue repeating the hour long tests. Step #3 add a hopper bin to hold more wood for longer run time. Many new users want 24/7 operation, but it’s not practical in terms of feedstock preparation time, oil changes etc. Long time users usually focus on power conservation first. Then operate their machines in a morning batch run and an evening batch run.


What feedstock does it take?

It takes chunked or thick chipped wood. It does not use rice husks, mulch, bark, etc. It’s a wood gasifier. How is that for truth in advertising! The size of the wood will depend a bit on engine size. Small engines can use chips as small as 1/2″ x 1″ x 1/4″. As large as 1″ x 2″ x 2″. Large engines prefer larger chunks. 2″ x 2″ for hard woods for beginners. 3″ x 3″ for soft woods.

Pine, fir & oak are popular woods to use. Plenty of others will work. Avoid cotton wood because it’s ashy and low density. Cedar can be oily. Give it a test. Mix with other woods if necessary. Try to keep it 20% moisture or below when beginning. Advanced operators can use a condensing feed hopper and use woods up to about 35% moisture for chunks. 30% moisture for chips.

The exception to the above is if you are just going to make gas for heating purposes. If it’s not going to go inside an engine, then you have a much wider range of feedstock size, but still try to keep the wood nice and dry. You can flare your gas into a thermal mass in a greenhouse for example for heating value.


What is the run time?

It depends on fuel density. The unit in the book ran a small 3 cyl. water cooled engine for 1 hour at 5kw load. When you add a feed hopper you can greatly extend that run time to many hours. It’s even possible if you have the skill to add some form of automated feed system, but batch runs are preferred for new users and lower cost.


What engine do you recommend?

Run what you have. Start with something old and cheap if you have it, while you practice. On the small end, a 1 liter’ish, 2 cylinder v-twin is a good engine. One to consider is a welder/generator by Miller. You can even get it fuel injected, so that you don’t have to accommodate a carburetor. If you want to run a smaller engine, store gas in a membrane and then run the small engine on stored gas.

On the larger end, you could also scale up to a 5 liter v-8 stationary generator too. Sizing of the hearth is outlined in the book. To learn how to hook up an engine, see our Electronic Carburetor Workshop book on the order page.


Can I make a business selling wood gasifiers?

If you make a machine for a buddy as a one-off that isn’t a business, its a project. Be smart about it.

If you want to make a business, really know your stuff and be willing to do it all on your own.


Can I use a stick welder to weld this gasifier together?

You bet! It will take a bit longer and be a little smokier, so please use a good exhaust fan. Much of the metal on the machine is 1/8″ – 1/4″ thick, perfect for 7018 rod. The cooling tubes and lid are 16 gauge, so turn your machine down and use a 6013 rod.


What about using pellets?

NO! Pellet quality varies quite a bit by manufacturer, feedstock and how it’s stored. I’ve played with them quite a bit in the past. They explode into sawdust in a sealed environment.

I like wood chunks because it’s more stable and repeatable across the country and low ash content. Pellets can include grasses and other biomass that has ash that fuses at high temperatures into little limestone looking rocks. Bark in pellets is a challenge too.

There is a process that solves most of the problems of pellets called torrefaction. It heats them up until they are pre-charred, so moisture breakdown and storage are no longer a problem. Someday when pellets are sold this way they will make total sense to use in a gasifier, with only minor adjustments to the hearth area.

In places in the world that use low quality biomass they tend to run their gasifiers cooler, which does cause some tar and they go to great lengths to filter the tar. It’s better to just crack the tars using wood chunks.