Hello,
Free wood would mean to me something like this:
Cut, split, dried, delivered and stacked near where I was going to burn it.
Other than that there are costs involved and when it comes to a wood say like mature horse chestnut and I have to split it, the cost outweighs the return - to get overly bogged down in the language of economics.
But I do also revel in burning particular woods in particular form, lets say split cherry, oak, pseudo acacia, apple, birch as our Swedish and Finish friends know all to well. And because of being something of a thrill seeker I even like burning some of the conifers we sometimes have available. I dream and then wake to the cruelty of still having 15 m3 of poplar out back to get through....
Greetings,
Don Wagstaff
Even more astonishing than a wood burner in a truck is a truck with a computer, but that is just me.