Getting dry wood chips
The calorific value of wood is directly linked to its moisture content. For maximum efficiency from an automatic boiler, dry chips — below 20% moisture — are essential. Two methods achieve this: chip already-dry wood, or chip on felling and let fermentation do the work.
Moisture — the enemy of efficiency
In theory, automatic chip boilers can burn moist wood — their combustion regulation system adapts. But the higher the moisture content, the greater the fuel consumption: part of the energy released by combustion is used to evaporate the water in the wood, and is lost as steam in the flue gases. This moisture in the flue gases also increases the risk of flue fouling and, consequently, chimney fires.
Two methods produce sufficiently dry chips. They differ on one fundamental point: the moment of chipping — before or after the wood is dried.
Chipping already-dry wood
This approach consists of leaving the wood to dry in log or roundwood form before chipping. Chipping can be done directly next to the boiler silo, just before use.
- Compact storage — logs take up less space than bulk chips
- On-demand chipping, directly feeding the silo
- No intermediate chip storage required
- Multiple handling operations before chipping: felling, splitting, storing, reloading
- Small branches cannot be recovered
- Dry wood puts more strain on the chipper: more frequent blade sharpening, higher vibration
- Hard to reliably get below 20% moisture; risk of moisture recovery during storage
- More dust produced during chipping
Chipping on felling and drying through fermentation
This method consists of chipping the wood immediately after felling, then leaving the chips to ferment in a heap for a few months. Active fermentation dries the chips naturally without any external energy input.
- Full valorisation of the felling, including small branches
- Fewer handling operations (see comparison table)
- Clean site after chipping — no residues to remove separately
- Chipper less stressed on green wood: higher throughput, less blade sharpening
- Can reliably reach below 20% moisture (down to 15% observed in practice)
- Virtually no dust produced during chipping
- Requires intermediate storage during the fermentation phase (3 to 5 months)
- A suitable silo loading system may be needed depending on the site layout
If site constraints — terrain, access, volume — allow chipping on felling, Method 2 is clearly preferable. It reduces handling, protects the chipper and produces better final moisture content. The only real cost is the intermediate storage space required.
Moisture content and chipper longevity
The method chosen has a direct impact on the behaviour and service life of the chipper. Chipping dry wood — whether treated, aged or simply stored a long time in log form — puts far more strain on the cutting components than chipping green wood. Blades blunt faster, mechanical stresses are higher and hourly throughput is lower.
Chipping on felling, by contrast, offers the best operating conditions: green wood is easier to chip, throughput is higher and sharpening intervals longer. This is why, all else being equal, we always recommend chipping immediately after felling.
Green wood cuts more easily, noticeably increasing the chipper's hourly output.
Blades blunt more slowly on green wood — less downtime for maintenance, more productivity on site.
Lower loads on the cutting disc, bearings and drive train — extending the service life of mechanical components.
Green wood produces fewer fine airborne particles during chipping — a benefit for operators and surrounding equipment.
Chip on felling? Our Super-Pain chippers are built for it.
Green wood, all species, small branches or large — our chippers guarantee a consistent chip from the moment of felling, with no sawdust or tailing, ready for fermentation and the boiler.