Moisture and energy content of different firewood species
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When it comes to heating your home with firewood, not all wood is created equal. Different species of trees have varying energy content, which affects how efficiently they burn and how much heat they produce. Let's explore the energy content of various firewood species, with a particular focus on larch softwood.
Energy Content Comparison
The energy content of firewood is typically measured in kilowatt-hours (kWh) per oven-dry tonne. Here's how some common species stack up:
1. Hardwoods:
- Ash: Approximately 5,000 kWh/tonne
- Oak: Around 5,000 kWh/tonne
- Birch: About 5,000 kWh/tonne
2. Softwoods:
- European Larch: Roughly 5,000 kWh/tonne
- Douglas Fir: About 4,800 kWh/tonne
- Sitka Spruce: Approximately 4,600 kWh/tonne
It's interesting to note that larch, despite being a softwood, has an energy content comparable to many hardwoods source.
Factors Affecting Energy Content
While species is one factor, there are other important considerations when choosing firewood:
1. Moisture Content: This is arguably the most crucial factor. Freshly cut wood can have a moisture content of 50% or more, which significantly reduces its energy value. Properly seasoned wood should have a moisture content below 25%.
2. Density: Denser woods generally provide more heat per volume. Hardwoods are typically denser than softwoods, but larch is an exception, being one of the denser softwoods.
3. Resin Content: Softwoods often contain more resin, which can increase their energy content but may also lead to more creosote buildup in chimneys if not properly and completely dried (why we sell our softwoods kiln dried).
Spotlight on Larch
Larch is an interesting case in the world of firewood. As a softwood, it's often overlooked in favor of hardwoods. However, larch has several characteristics that make it an excellent firewood choice:
1. High Energy Content: With about 5,000 kWh/tonne, larch matches many hardwoods in energy output.
2. Relatively Quick Drying: Larch tends to dry faster than many hardwoods, reaching optimal moisture content sooner.
3. Pleasant Aroma: When burned, larch produces a nice, resinous scent that many find appealing.
4. Availability: In many areas, larch is more readily available and is always much less expensive than hardwoods.
Practical Considerations
When choosing firewood, it's not just about energy content. Consider these practical aspects:
1. Storage: Proper storage is crucial to maintain low moisture content. Keep wood off the ground and protected from rain.
2. Use both: Consider using a mix of hardwoods and softwoods. Use softwoods like larch for kindling and initial fires, and hardwoods for longer-burning heat.
3. Local Availability: The most energy-efficient wood is often what's most readily available in your area, reducing transportation costs and environmental impact. This is why Scottish sourced softwood has such a good energy profile
In conclusion, while hardwoods are often touted as the best firewood, softwoods like larch can be excellent choices. With its high energy content, pleasant aroma, and quicker drying time, larch is a firewood option worth considering. Remember, the key to efficient burning is properly dried wood, regardless of species.
Sources:
https://cdn.forestresearch.gov.uk/2022/02/fr_bec_wood_as_fuel_technical_supplement_2010.pdf