Heating a hot tub off grid

[Ryder]

OK so my hot tub would not be wretched excess....it would be theraputic .  I have a smaller non functioning hot tub and i live where there is an abundance of pine beetle killed firewood (regular postings on craigslist to just come and haul cut down trees away. I was thinking of some sort of simple eficiant way to heat water with wood. what comes to mind is a thermo siphon type stove and stovepipe heater using black gas pipe for the water to run thru a stove and inclined stove pipe that would be below the water level in the tub but not in the tub just adjacent (I have seen the immersion type heaters). another idea would be a coil of black plastic pipe with my small solar foutain pump to circulate the water when the sun was shining on the solar panel and of course on the black plastic pipe. has anyone seen some ingenious setup that is long on scrounged parts and not too high tech. I don't expect to have a year round set up but for three seasons it would be nice for a hot soak after a long day in the garden or job.   

[Atash Hagmahani]

I dunno, but woodfire-heated hot-tubs do exist, and I bet you can find plans.

[opsec]

How about incorporating a rocket stove into the design of the tub. Shouldn't take too much engineering from the stove designs I've seen.