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.
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.
Below 20% moisture. How to test? The “crack test.” Hit two pieces together. Dry wood makes a sharp, ringing crack. Wet wood thuds.
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.
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.
John McGrath, a homesteader in the Appalachian foothills, had spent three days clearing storm-damaged oak from his back forty. The trunk went to the sawmill. The branches—tons of them—went into a smoldering, smoky burn pile. That night, watching the news report on diesel prices hitting $5.50 a gallon, he did the math. He was literally burning energy to get rid of energy.
“I felt like a caveman,” he says. “Digging a hole to bury gold.”