Wood Gasifier Builder--39-s Bible- Transform Tree Branches Into May 2026

Your job as a builder is to maintain that zone. Too wide, and you lose heat. Too narrow, and you choke airflow. The “Bible” method: Start with a 4-inch throat for a 10 kW generator. Taper it by welding a stainless steel cone. It’s crude, but it works. Raw wood gas carries tar and ash. Tar will gum valves and rings in under ten hours. Ash will score cylinder walls.

Don’t modify the carburetor. Instead, build a “mixer” that fits between the air filter and the carb throat. It’s just a pipe with a venturi (a narrowing) and a needle valve to bleed in extra air. Your job as a builder is to maintain that zone

That was eight years ago. Today, John’s tractor runs on twigs. His backup generator hums on wood chips. And his “Wood Gasifier Builder’s Bible”—a dog-eared, grease-stained three-ring binder—contains the accumulated wisdom that turned a nuisance into a power plant. The “Bible” method: Start with a 4-inch throat

Because branches are small, you can solar-kiln dry them in a $50 greenhouse frame. Clear plastic, pallet floor, ridge vent. Six weeks in summer. Three months in shoulder seasons. 2. The Heart of the Beast: The Reduction Zone Every gasifier has a narrowing, a throat, where charcoal glows at 1,800–2,000°F. This is where carbon dioxide turns into carbon monoxide—the actual fuel gas. Raw wood gas carries tar and ash

When the next ice storm takes down power lines for a week, your generator runs on the branches that fell with the lines. When diesel hits $7 a gallon, your tractor doesn’t care. When the supply chain stutters, you look at the woodlot and see a full tank.

John McGrath’s original “Bible” has now been scanned and shared online. A free PDF version, including dimensional drawings and parts lists for three different gasifier sizes, is available through the Open Gasifier Project.

From the branch, a flame you cannot see. From that flame, the power to move mountains of stone. And from that power, freedom from the pump.