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. In Russia, stove heating is quite widespread in rural areas, as the main or backup source of heat. Birch is usually used as firewood in my region and occasionally, about once a month, they heat the stove with aspen to clean the chimney and reduce the risk of fire. Oak and walnut are almost never used as firewood, because these tree species are not common in my region. The main rule for stove heating is that firewood must be dry, ideally you need to store firewood for the next year, and heat the stove with last year's stocks.