Calorific value by wood species
Which wood gives off the most heat? The question is usually put the wrong way round. Here are the figures that exist, and the places where none do.
Per kilogram, every hardwood has practically the same calorific value. What differs is density - how many kilograms fit into a loose cubic metre. Denser wood therefore burns longer, not hotter.
Calorific value per kilogram
What matters is not the species but the water content. From dry to freshly felled, the same wood loses more than half its energy.
| Water content | Softwood | Hardwood |
|---|---|---|
| 0 % | 5.20 | 5.00 |
| 15 % | 4.32 | 4.15 |
| 20 % | 4.02 | 3.86 |
| 30 % | 3.44 | 3.30 |
| 50 % | 2.26 | 2.16 |
Figures in kilowatt hours per kilogram.
The ranges by density
Sorted by density, densest first. The energy column gives the value per loose cubic metre at 20 % water content - but only where the source has one. For six of the ten ranges there is none, and then a dash stands here instead of an estimate.
| Range | Density | Energy per loose m³ |
|---|---|---|
| Hornbeam | 750–820 | – |
| Robinia | 700–750 | – |
| Beech | 680–720 | 1,346 |
| Oak | 670–710 | 1,377 |
| Ash | 650–690 | – |
| Maple | 620–660 | – |
| Birch | 600–650 | – |
| Sweet chestnut | 540–590 | – |
| Softwood | 430–520 | 865–984 |
| Lime / Poplar | 400–530 | 811 |
Density in kilograms per cubic metre at 12 to 15 % wood moisture, energy in kilowatt hours per loose cubic metre. The two columns come from different sources, each using its own densities, so the order does not match exactly everywhere.
Water content is not wood moisture
The two figures are constantly confused. Common meters show wood moisture, the trade calculates in water content. For 20 % water content the meter has to read 25 %.
| Water content | Wood moisture |
|---|---|
| 5 % | 5 % |
| 15 % | 18 % |
| 20 % | 25 % |
| 30 % | 43 % |
| 40 % | 67 % |
| 50 % | 100 % |