Firewood?
Sustainable?
How about: *polluting*, *extremely unhealthy* the reason firewood is not used that much anymore is because of the problems it comes with. Wooden gas burner is not a solution, think about the environment as well, how many wild trees would be cut down just because people will try and sell it illegally once the prices sore. It's not an alternative, is not an option, we all need to learn about environment friendly options and at the end make things better not just for us but for our future generations as well.
The suggestion to burn firewood is a retrograde step. We moved from firewood to natural gas many decades ago. It is retarded to even think about going back. Firewood is neither environmentally friendly, nor healthy. It produces much more soot and ash, when compared to natural gas. I am not saying that natural gas is the safest option that is available. But at least with natural gas, the pollution levels are much lower when compared to firewood and coal. People come up with all sort of crazy suggestions when there is a shortage of natural gas. This talk will just die down when gas becomes more abundant again.