Processes & Measurements
How is firewood volume measured?
Our bulk bags are ‘loose-filled’, i.e. dropped into the bag from a conveyor. The logs are therefore not stacked in the bag. We know the volume is correct as we check the volume in a metal cage measuring 1m x 1m x 1.2m or 1.6m tall. Fill these to the top, and we confirm the volume is correct.
The little bags have the logs packed by hand, so they are termed as ‘stacked’ volume, and each bag contains 0.02m3. That makes it confusing, but it’s a HETAS requirement to declare volumes. However, the following table converts everything into a ‘loose-fill’ equivalent to simplify things.
Firstly, the 1.2m3 bulk bag holds approx. 43 small bags and the 1.6m3 58 small bags, so the bulk packs convert as follows:
How do you process firewood?
- When wood is delivered to the yard, it is size graded and where possible sorted by species.
- The large processor has a computer which measures the length and diameter of the wood and ensures logs are cut and split to meet the desired specification.
- Any larger logs go to a secondary splitter to ensure they are split down to size.
- Final specification logs are taken across a grader/cleaner to ensure all loose bits are removed. These bits are then shredded and taken to the boiler to provide heat for the kilns.
- The logs are air dried for up to 4 weeks to begin a natural drying process. They are then placed in metal cages into the kilns. We place 18 tonnes in a kiln and take 12 tonnes out – so, we remove 6,000 litres of water each time.
- Once dry, after about 40-50hrs, the logs are moisture tested to ensure they are below 20%.
- When packing our bulk bags, the wood is passed over conveyors which not only removes any further waste but also provides another opportunity for a final quality inspection. When packing the small bags, these are hand selected into the final packs, and any out grades discarded.
- Final moisture content check is conducted before logs are packed.
Loose volume vs stacked
Firewood is supplied and therefore measured in two forms:
- Loose volume – this is how we supply and declare our bulk bags and the term arises from the fact that the logs are tipped into the bulk bags. In order to confirm our volumes, we periodically tip the bulk bag into a solid sided crate which measures 1m x 1m at the base. The height of the crate, so in our case, 0.8m, 1.2m or 1.6m will determine the final volume. If the height is 1.6m, then the volume in the crate is confirmed as 1m x 1m x 1.6m – 1.6m3.
- Stacked volume – this is where the logs are neatly stacked and therefore they take up less space than ‘loose’ volume.
Woodsure use the conversion principles from the Food and Agriculture Organisation of the United Nations: Wood Fuels Handbook.
1m3 of loose fill bulk (dumpy bag or loose load) = 0.6m3 neatly stacked
1m3 neatly stacked (crate/logstore) = 1.67m3 loose fill