wood fire powered open thermosyphon for radiant floor

I tried to hack another thread, but I'll start one here.

I have radiant tubes in my earthen floor that I used to have hooked to pumps and a propane tankless heater.  I don't like using the electricity for the pumps and all that propane, so I've been thinking about an outside-the-house system that would use a coil of pipe (probably copper, as big as I can get locally, maybe 3/4", 50') and put that coil in a fire.

I think the success of this is going to rely on keeping the coil below the grade of the floor and having an open-to-the-sky "pot" (probably only a 5 gal thing) on the return line.  That way, the hot water will zip uphill through the floor, heat the floor, lose heat, and go back to the return 'pot' that has edges *higher* than the floor grade.  

I can use PEX at a decent distance from the fire, insulate the uphill portion so as not to lose heat, and even have disconnects so I can put it away for the summer.

Basically, I'm making the floor run part of the uphill run of the thermosyphon.

I've attached a quick drawing with what I hope are decent labels.  I'd love to hear from this crowd if you think it could work or what problems you might see.

It will work if the lines through the earth are large enough for thermosyphoning to occur.
If pumps have been there before I would expect the ytubes to be small, and if too small water will have too much resistance from the pipe to actually move.
Why not set up a solar system to run the pump?

Did you complete this project? I built a thermosiopon hot tub last year, and am hoping to figure out radiant floor heat for an off-grid residence I’m going to start work on this summer. Seems to be precious little info on feasibility & tech specs for this kind of system. I’d love to hear how this went for you.

You could still use a pump, maybe even a slower, less energy hungry pump, and still get all the benefits of growing your own fuel. And the energy that the pump uses gets sent to the house to warm it up, so it isn't a total lost, and if you time the fire to burn during the day, the pump could be powered by solar panels.