I will have to say yes... If you have ever heard of a pit pig. Basically a smolding pit which cooks a full pig. So if you put say firewood or another heat generating source into say stainless steel container under your soil where it had a hatch top it could work. As for extracting the heat from it that is also simple wrap it in a steel pipeline with vent access to the air away from the exhaust and air intake of the "fire". Then lay concrete around that you should end up with a solid fixture that could easily be cleaned each summer.