Wood fired hot tub, mono boiler - Video

So I took a 100lb propane tank and cut out a 6 inch wide hole centered at the top and bottom. Then I ran a 1/4inch thick pipe through the length of the tank, with a foot sticking out the top, and welded the seams. Then I made a low and high point on the tank and welded couplers for 1 inch threaded pipe. You can see where I have pipe coming out of the couplers going to clamped radiator hose.

There's a low and high on the tub. Once the water gets luke warm it really starts to thermo syphon and it gets extremely hot.

It was in the mid 50's when I did this. I could see having to insulate whatever tub you're using and having a real insulated lid