Nobody uses oak or walnuts for heating, and msot have changed to pellet usage for their homes, and those are made out of willow and fake acacia trees, they grow damn fast, are easy to be cut and processed, and require the least energy, mix it wid leftovers from other wood industries and they are pretty effective.
Nobody will use that wood in Germany which if I remember correctly is where you live, or wherever you live. But I please don't deny what I can see with my own eyes.
Also, are you talking about using that wood for small metal stoves or the large stone fireplaces that are built in houses?
For the latter, oak and walnut wood are ideal:
Oak firewood is absolutely one of the best types of firewood you can burn. Oak firewood has a big minus. Oak takes a very long time to dry. And as a rule, firewood is sold immediately after the tree has been cut down.
Therefore, you will have problems lighting the stove, or you will have to chop wood into smaller chips and use lighter fluids. Pine, birch, aspen dries very quickly.