Wood Gasification Boilers: Off-Grid Heat That Actually Works

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A wood gasification boiler is one of the few heating appliances where the physics genuinely reward the operator. You load timber, the unit pyrolyses it into a combustible gas, and that gas burns at temperatures a conventional firebox never reaches. The result is more heat per cord, less creosote in the flue, and a flue gas that is mostly water vapour and carbon dioxide. This piece covers the spec sheet, the safety case, and the practical bits I've learned running heating off the grid in Central Queensland.

What Gasification Actually Means

Plain wood combustion heats the surface of a log. Gasification goes further. When wood sits in a high-heat, oxygen-starved zone — roughly 150–260 °C — it thermally decomposes into a syngas made up of hydrogen, carbon monoxide, methane, and tars. That gas is then drawn into a separate, very hot combustion chamber where it burns.

The relevant numbers:

• Wood contains about 19 MJ/kg on a dry basis. Roughly 60–70% of that energy sits in the gases released during pyrolysis, not in the char.
• The combustion chamber in a gasification boiler runs at about 980–1,090 °C.
• The exhaust is overwhelmingly water and carbon dioxide, with very few unburnt byproducts.
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