What are the stages of wood combustion?

You have placed the Wood logs in the Firefox of your wood-burning appliance, then the small logs and the firelighters according to the recommended reverse lighting method. You then struck the match and set the firelighter alight, this is the beginning of the drying phase.
It is called the drying phase because wood, even when considered dry (<20% humidity), contains water, often in the form of residual moisture.
When lighting the fire, and under the effect of heat (temperature below 150°C), this water will evaporate. No combustion has yet taken place, but this phase is essential to prepare the wood to burn efficiently.

It is during this phase that we realize the importance of drying the wood:
- Wetter wood takes longer to dry, it consumes more energy and needs more time to enter the pyrolysis phase.
- Dry wood (with a humidity level of less than 20%) is synonymous of better efficiency and therefore better energy performance. It's also more comfortable for the user.
- The lighting technique known as "top combustion’ or ‘reverse ignition"is essential because it contributes to the temperature rise and therefore the drying of the wood logs.
- Finally, note that excessive release of white vapour is a sign that the wood is too damp...

Where the moisture has evaporated, we can move on to the pyrolysis stage (the rest of the moisture will evaporate progressively). At around 150°C, the wood begins to chemically decompose. This decomposition produces:
- Combustible gases (including carbon monoxide (CO), methane (CH₄), and various hydrocarbons).
- Charcoal, a solid residue rich in carbon.
Around 225° and in the presence of oxygen, the gases released ignite, forming flames.
Around 300° is the ideal "cruising temperature", it is the top of pyrolysis. The blaze, as we imagine it, continues as long as the necessary ingredients for the reaction are present.

The advice of Cheminées Poujoulat:

- A sufficient supply of oxygen must be maintained so that the combustible gases ignite rather than condense. Without a sufficient supply of oxygen, pyrolysis is incomplete. This produces tar and soot which will clog the smoke exhaust duct.
- It is to avoid this risk of clogging that it is recommended to carry out blaze at full speed rather than at under speed. This is also why it is essential to choose an appliance that is neither undersized nor oversized.

3. Coal combustion or oxidisation

When the pyrolysis phase ends, what remains is mainly glowing charcoal wood: the embers. Temperatures between 600° and 800° are reached. The charcoal then burns slowly with intense heat and few flames.
This phase produces carbon dioxide (CO₂) and heat, with relatively stable and complete combustion.

As we go along, the quantity of carbon will decrease and the fire will gradually die out. Ashes will remain, which is a residue composed of non-combustible mineral compounds present in the original wood or coal (calcium, potassium, magnesium).
These ashes can be used for different domestic purposes: household maintenance, enriching vegetable garden soil, composting. Here we tell you how to use them.
With wood, nothing is wasted.