EN-02 · 02 Energy
Rocket mass heater
A high-efficiency wood burner whose exhaust is run through a cob or masonry bench, so a small stick-fire heats a room for hours after it is out.
Origin
Ianto Evans, Leslie Jackson and the cob-building community
Materials
- Firebrick for the burn tunnel and heat riser
- A steel barrel or ceramic bell
- Cob, stone or masonry for the bench mass
- A well-drafted chimney
Method
- 01
Learn the J-tube geometry before mixing cob. A bad burn tunnel cannot be decorated into a good one.
- 02
Build on a non-combustible base with clearance from timber. This is a heating appliance, not a sculpture.
- 03
Insulate the heat riser so the burn stays hot and clean. The mass comes after the combustion, not around it.
- 04
Run the exhaust through a long, slightly rising channel inside the bench, then to a chimney that drafts in all seasons.
- 05
Burn only dry, small-diameter wood. A rocket that is fed like a fireplace will smoke and glaze.
What this makes possible
- A heated room from a fraction of the wood of an open stove
- A bench that remains warm after the fire is dead
- A craft that a household can repair without a service contract
This is a field record, not a permit. Adapt to local law, climate and skill. If you have run this method, send what you learned.