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Four things you should know about firewood


Firewood, a commodity, renewable and eco-friendly if used correctly.

Whatever you think about firewood, it's an incredible asset, and the sense of being self-sufficient from nature is a source of satisfaction.

At Kellfri, we have been selling firewood products for more than 50 years. We have now compiled information from firewood users, other experts and included our own experiences and competency relating to this topical subject.

This guide contains:
1. Different types of wood have different energy contents
2. What everyone should know about pulpwood
3. The best season and the right machine for cutting and splitting
4. Correct moisture content in chippings

1. Different types of wood have different energy contents

Different types of wood contain different amounts of energy; in simple terms, the heavier the wood, the more energy it has.

A basic comparison is how much firewood is required to replace a cubic metre of oil where the firewood is measured in solid cubic metres (m³s).

• Spruce 6.0 - 6.5 m³s
• Pine 5.8 - 6.5 m³s
• Birch 4.8 - 5.2 m³s

A more exact measurement is Kwh/m³s at 20% moisture content.

• Pine 2,360 kwh
• Spruce 2,320 kwh
• Birch 2,820 kwh
• Oak 3,600 kwh
• Aspen 2,190 kwh
• Dry spruce 2,230 kwh

But the energy content in firewood is unstable. It is important to season the firewood correctly to keep as much of the energy as possible. With this guide, we want to help users of firewood to season their firewood correctly. Stacking pulpwood for too long leads to a fast reduction in energy content through, for instance, storage decay and other fibre-decaying processes, and the firewood simply starts to rot.

Branches and needles contain more energy thanks to a richer lignin content and other energy-rich compounds, and these are well suited for use as chippings.


2. What everyone should know about pulpwood

It is best to fell the firewood in winter, as it contains the least amount of water. As the trees begin to pump water up into the trunk during the spring, the water content can be quite significant in comparison.

Stack the pulpwood on a covering to avoid direct ground contact; it will still dry out even it has not been split. If the firewood has to be handled manually, it is practical to cut the pulpwood in shorter lengths which are easier to handle.

If the wood is used to heat a boiler, it doesn't matter greatly what type of wood you chop in the forest. If, on the other hand, it is to be used in open fireplaces, then birch is the best option.

Softwood spits due to its resin content which is very high in energy. Resin is generally found in softwood and also collects in so-called pitch pockets, which are small cavities in the wood filled with resin. When these are heated up, small explosions occur that cause sparks and soot to fly out of the fireplace with the risk of fire as a result.

And remember not to burn mountain ash either, as the Brownie will move on! If one is to believe at all in old wives tales...


3. The best season and the right machine for cutting and splitting

The best season to split firewood is in the spring. It dries quickly during the spring as the air is usually drier compared to the more humid air of high summer. The best option is to cut and split next year's firewood, as it can be difficult to dry the wood in time if it is to be used in the autumn. Good planning is essential when it comes to handling firewood.

There are many solutions in terms of cutting and splitting, ranging from bow saws and splitting axes to firewood processors with transfer decks and conveyors that both cut and split large volumes in a short period of time.

The procedure still involves cutting and splitting; cutting firewood with a chainsaw entails maintaining the same level of safety, protective equipment and knowledge as in the forest! The injuries are still the same whether they occur by the woodpile or in the woods, so never work alone with a chainsaw.

When the logs are cut, they can be split using electrical hydraulic log splitters of varying sizes and tractor-driven hydraulic log splitters for tougher tasks. The electrical hydraulic log splitters are versatile and easy to move, and do not require a tractor. However, certain models require a 16 amp outlet. The tractor models are usually more powerful and often manage to split logs up to a metre in length, and they are also easy to move to where the wood is.

The advantage of firewood cut in metre lengths is that it is quick to stack. It can also be stored outdoors if it has been correctly protected from the elements. A suitable approach is to split firewood cut in metre lengths, store it and then cut and split it again the following year when the wood is needed. Make sure to put a covering under the woodpiles to avoid ground contact.

Split wood is best stored in firewood sacks stacked on pallets, as this protects it from moisture, and the meshed design of the sacks lets plenty of air in. Adding a frame around the pallet in which the bag hangs helps, as this enables the sacks to be properly filled. Even better is to take the time to actually stack the firewood in the bags, as then they can hold 15-20% more, and this also makes the bag stable.

Small bags roughly 60 litres in volume are also available for more commercial sale of firewood. These are easily filled using fit for purpose equipment. A steel chute is filled with the right quantity and then tilted into the bag.

1.5 m³ big bags with eyelets are filled directly from a conveyor. The eyelets make is easy to move the bags using a tractor or similar, and make handling efficient and simple.

A firewood chopper is a machine which uses a powerful hydraulic ram to split and cut firewood to the correct length all in one step. If the logs are small, cutting several of them at a time is possible.

Let's move on to the firewood processor which is fitted with a transfer deck (work table), offers very high capacity and is well suited for use by contractors and those requiring large-scale management of firewood that is for sale. The machine processes the firewood in a sequence from feeding in the logs, cutting and splitting them into firewood and transporting it to sacks, a woodpile or trailer.

Overall, you have to assess your requirements and how much you would like to invest. There is no shortage of equipment to suit all needs and combinations.

It's important to carefully comply with the manufacturer's instructions for operation and maintenance, as incorrect use or damaged and faulty protection equipment can make using the machines dangerous. Take care of yourself!


4. Correct moisture content in chippings

Chippings can be used as an alternative to wood for heating, but different equipment is required to take full advantage of the energy content. In general, one can say that chippings in smaller heating plants should maintain a moisture content of no more than 15-20%, and the chipping size should be uniform and not exceed 50 mm in order to avoid breakdowns.

It is best to dry the wood or brash before chipping to achieve the correct moisture content. Cold air drying of the chippings is also an alternative. A moisture content that is too high not only has a negative impact on the fuel value, but there is also a risk that mould can take a hold in the chippings pile and the dust that this causes can lead to the serious illness of hypersensitivity pneumonitis.

A chipper with enough capacity is a must, and setting options are also important. A branch crusher to prevent long splinters and easy service access to quickly replace or sharpen the blades are also important issues.

There are different chipper sizes that can handle various wood thicknesses. They are often fitted with a deep infeed hopper to increase operator safety. It is important to be able to spread the chippings evenly, so it should be possible to adjust the chipper's discharge angle. Being able to adjustable infeed speed and forward/reverse feeder roller functionality are also important features for using the machine, as this increases performance and versatility.