I don't see the point of looking for firewood unless they mean going to look for firewood themselves, not buying it, because firewood is expensive. Very expensive. And the ideal firewood for fireplaces, such as oak or walnut, is the most expensive.
Is it allowed in Germany to go to the forest and cut firewood? With so many environmental regulations, I wouldn't be surprised if it was forbidden or you had to ask for permission and pay a fee.
Bamboo trees are a very good source of heat considering their short maturity period, less toxic nature, and ability to dry fast. But it doesn't have the ability to retain heat for a long time. One needs to have plenty of it to heat a house for a very long time which might increase the amount of fume and ashes produced.
That's what I thought. I hadn't heard of bamboo as firewood, but being a thin shrub that grows fast, it's not likely to last long.