The heat locked up in a fuel is expressed as its ‘calorific value’. Now, a laboratory will tell you the calorific value of wood is around 8,600 Btu’s /t. They would have used a bomb calorimeter to burn a sample of wood completely whilst measuring the amount of heat produced.
This is all very academic and bears little relation to what occurs when you throw a log on the fire. However, the results nevertheless are interesting in that there is a very close correspondence between the calorific value of all types of wood fibre, as stated in the ’Burning dry wood’ section.
In other words, whether you are burning beech or balsa wood, they match each other very closely in terms of calorific value.
What does change is the density. So although different species of wood produce similar calorific values when seasoned, their bulk quantities will vary drastically. For example, to obtain a similar heat output from spruce as beech, you will need an extra 50% of storage by volume.
This is the main reason we stick to hardwood as our fuel supply. The volumes and storage space required by you, the customer, are lower, which in turn results in fewer deliveries and less handling by us and you.