replying to The Daring Dufas, Ray wrote:
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.

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