(M.U.V. DE WADDENEILANDEN)

The heat that firewood gives off is expressed in power per kg, Kw/kg. The power for virtually all types of firewood is between 5.1 and 5.3 Kw/kg. That's crazy, you might think, because we all know that oak is better “quality” than poplar, right? But then you are missing something, because a block of oak weighs more than a block of poplar, so you need many more blocks of poplar than oak to get one kilo. That is why volume is used in the calculation. The amount of energy a certain type of wood emits is expressed in calorific value per m³.

Here is a list of the calorific values ​​per m³ of different types of wood:

• Oak wood: 11.4 GJ/m³
• Beech wood: 11.4 GJ/m³
• Birch wood: 9.1 GJ/m³
• Ash wood: 11.4 GJ/m³

This makes it clear which type of wood really produces more heat than gas, for example.
Gas produces 1 GJ of heat per approximately 35m3, which means that approximately 350m3 of gas is equal to 1m3 of oak!