Wood chips are defined as wood that has been mechanically shredded into pieces measuring just a few centimetres in size. These small pieces of wood are burned in fully automated combustion plants and offer the same level of convenience as their fossil fuel counterparts.
If you use wood chips for your heating system, you can use the following comparisons as a guide. One solid cubic metre (fm) of wood yields 1.4 cubic metres (rm) and 2.5 loose cubic metres (srm) of wood chips.
| Wood chips (average) | Log wood | Pellets | Heating oil | Natural gas |
|---|---|---|---|---|
| 2500 kg (air-dry) | 2500 kg (air-dry) | 2000 kg | 860 kg | 840 kg |
| 12,500 l | 5000 l | 3,500 l | 1,000 l | 1,000,000 l |
| 12.5 m³ (srm) | 7.5 m³ (rm) | 3.5 m³ | 1 m³ | 1,000 m³ |
The quality of wood chips plays a key role in ensuring the optimal operation of the heating system. Due to the large number of producers and the variety of wood species, wood chips are a raw material with a wide range of characteristics. The PuroWIN is approved for wood chips of grades P16S and P31S, as well as A1 and A2. When using these grades, we guarantee compliance with the prescribed emission limits in practical operation. This is achieved without the need for additional measures such as filter technology or pre-cleaning. For the system to operate ideally, wood chips with a moisture content of 20–30 per cent should be used.
- Store logs in a well-ventilated, sunny spot for at least one summer before chipping (for W25-30 wood chips)
- Wood chips with a moisture content > 35% are not suitable for storage (decomposition, mould growth, self-heating/fire hazard)
- During wet summer months, it is advisable to cover the wood chips
- Use natural, chemically untreated wood
- Ensure a low, uniform moisture content (no pockets of damp)
- The proportion of needles, leaves, fine twigs and bark should be low
- Uniform particle size is important
- The wood chips should have smooth-cut edges and not be frayed
- There should be no contamination or foreign objects in it
The calorific value varies depending on how coarse or fine the wood chips are, their moisture content, and whether they are made from hardwood or softwood. This means that different grades of wood chips require different quantities to reliably provide the specific amount of heat needed. You can find out approximately how much wood chips you will need for your system in the ‘Wood Chip Fuel Information’ leaflet.
Different units of volume are used for timber. A distinction is made between cubic metres, solid cubic metres and loose cubic metres. A cubic metre refers to stacked logs with external dimensions of 1 m × 1 m × 1 m. The gaps are included in the calculation. A cubic metre of loose volume, on the other hand, consists of wood that has been loosely poured into a container measuring 1 m x 1 m x 1 m. Here too, the gaps are included in the calculation. There are no gaps in a solid cubic metre. This consists of 1 m³ of solid wood with no gaps.
