Heating with wood without lighting a fire
A heap of chipped brushwood in fermentation can heat water to 60 °C for six months — without consuming a single gram of dry matter. Jean Pain demonstrated this as early as 1975. A technique that simultaneously produces usable thermal energy and a high-value organic soil amendment.
1975 — The first experiment
Jean Pain would check the progress of fermentation in his brushwood heaps by plunging a metal rod into them: the heat the rod gave off when withdrawn confirmed fermentation was active. The idea then came to him to recover this heat to warm water.
In 1975, Étienne Bonvallet — his technical collaborator and nephew, and future founder of Équipe Jean Pain — and Jean Pain built together a 50-tonne heap of chipped wood, branches and brushwood, inside which they installed a network of pipes. This network was connected to a natural water source flowing at 4 l/min at 10 °C.
"The power output of this first heap was approximately 14 kW — that is 250 W per tonne of material, or 60 W per m³. Energy extracted without consuming a single gram of dry matter."
From the first test to a practical installation
Encouraged by this first success, Jean Pain wanted to continue his greenhouse growing experiments and decided to heat the greenhouse using the same technique. A first installation was built using a network of straight stainless-steel tubes connected by flexible hoses — but the connections caused leaks.
Jean Pain then turned to flexible HDPE pipes coiled in a spiral inside a circular heap of 115 m³. This installation maintained a temperature difference of over 10 °C above outside temperature in a 210 m³ polytunnel greenhouse throughout an entire season.
Dismantling the heap revealed a new challenge, however: the flexible pipes, weakened by the intense heat inside, risked being damaged during mechanical recovery of the material. Several techniques were tested in the following years — all showed weaknesses or prohibitive cost.
A fixed water tank (plastic cistern) connected underground to the heating installation, which can be covered with freshly chipped material. The material can be recovered mechanically at the end of fermentation without dismantling the installation. The tank should have a capacity equivalent to one hour's flow of the heating system — the time needed for the water to rise to the core heap temperature.
Where does this energy come from?
The question is worth asking: if no dry matter is consumed, where does the recovered thermal energy come from? The most plausible hypothesis is that it is the residual energy of the bacterial activity responsible for fermentation — energy that may come from the water consumed by the bacteria, since it has been observed that if the heap dries out, fermentation stops and the temperature drops.
Energy production in the Jean Pain Method is not, and should never be, the primary goal of producing fermented chipped wood. The primary purpose is to produce a very high-value organic soil amendment. Heat recovery is only worthwhile within this framework — as a bonus that fits into a holistic valorisation process.
To achieve these results, it is essential to have a consistent, good-quality chip — neither too coarse nor too fine — that allows active, even fermentation to be maintained over the long term. An inconsistent chip, with large splinters or sawdust, produces uneven fermentation that compromises both the thermal output and the quality of the final soil amendment.
An exceptional double benefit
What fundamentally distinguishes the Jean Pain technique from all other wood energy applications is that the material is not destroyed — it is transformed. At the end of fermentation, the chipped wood turned compost constitutes a very high-value agronomic soil amendment, ready to be spread on crops.
- Material not consumed — transformed into soil amendment
- Dual output: heat + high-value compost
- Stable temperature for up to 18 months
- No combustion, no particle emissions
- Requires large volumes of chipped material
- Material destroyed — thermal energy only
- High efficiency (>92%)
- Automated feed from a silo
- Particle emissions (even if reduced)
- Suited to small and large volumes alike
To go further on ligno-cellulosic fermentation and its mechanisms:
The Jean Pain technique starts with the right chipper
Even fermentation, maximum duration, dual thermal and agronomic benefit — everything starts with a quality chip. Our Super-Pain chippers have been designed for exactly that since 1981.