Energy content

Fig. 1 Supplementary heat. The output
depends on fuel weight, moisture, and
boiler efficiency rate.

Wood has an energy content, i.e. the full heat generated during incineration. All wood has the same energy content per kg, but density and stacking methods make a difference. The energy content for fuel oil is 10 kWh/liter.

For example, there is a lot of space in a stere, where wood has been thrown haphazardly in a box measuring a cubic meter.


The energy content is the amount of energy released during incineration of one kg of a fuel.


1. Firewood

Stored, split beechwood has an energy content of 4.2 kWh/kg with a moisture content of 18% (Danish Technological Institute, webpage Household stoves).

2. Oil

The energy content in heating oil, which is similar to diesel oil, is slightly above 11 kWh/kg. Converted to liters it corresponds to 10 kWh/liter.


The energy content in firewood is affected by the amount of moisture, since the water must be heated and evaporated, and none of it contributes to useful heating. The moisture content is app. 18 % , if the firewood has been split and dried 1-2 years.

All types of wood have the same energy content, i.e. 4.2 kWh/kg. However, wood has differing weights depending on the amount of air pockets. Beech, oak, ash and elmwood are relatively dense, whereas pine and poplar are less dense. Danish tree species have densities which vary app. +/- 8% (Danish Energy Service, spreadsheet Beregning af braende energitjenesten2.xls).

Table 1. Selected energy contents (Centre of Biomass Technology, Overview of fuel energy content, factsheet 67).

Fuel Moisture content (%) Energy content (kWh/kg)
Straw, yellow 15 4.00
Straw, grey 15 4.17
Straw pellets 8 4.44
Corn 15 4.17
Beechwood, stored 20 4.08
Beechwood, fresh 45 2.61
Woodpellets 6 4.90
Heating oil 11.86

Also see

Created by tanja.groth. Last Modification: Friday 11 June 2010 11:48:42 CEST by tanja.groth.