I had an idea for one, never built it, but I am confident it would work if done correctly, based on some earlier experimentation I did.
You have a huge woodchip pile outside. Layered in is high temp rated (well, at least hot rated, my experiments show at least 160 degrees F within *minutes* of the pile being there) fluid pipe, maybe this pek stuff guys here use for their OWBs. Lots of loops back and forth deep in there, it gets warm from conduction (not too much, it needs to keep slow composting to get you some heat, this is a variable and would need to be fine tuned a little..). Now the pipe is run uphill to whatever space needs heated. Closed loop system, using like an antifreeze and water solution. Up there, just some loops around the floor etc, to act as the radiator.
And that's it. The loops of pipe pick up the heat, it gradually starts pumping itself uphill-towards your heated area. You want the part between your stilt cabin and chip pile to be an insulated conduit of some sort, so it doesn't lose heat just outside. Up in your cabin, the pipe loses the insulation and does its radiator action. It radiates off heat, gets colder, and wants to drop back down to the loops inside the chip pile, where the cycle starts again. The principle is called a thermosiphon. It's a completely closed loop thing, no electricity required. It would be better if it radiated off into thermal mass, but seeing as how this is up on stilts or something, I'd skip the 20 tons of like rocks...just saying...
I was going to build one for the greenhouse here, until the big diesel chipper broke...no chips, project on back burner until joe boss gets it fixed, which he claims might happen this year.
Now I have built ones that just used hot air, but I haven't built one using liquids as the heat transfer medium. Same deal though. real common in solar heating designs, I just like the idea of a compost pile better, as it is 24/7. I imagine you could plumb in a temp gauge valve dealie if ya wanted.
Thermosiphon - Wikipedia, the free encyclopedia
I used to be a big alt energy head, but I lost interest in it as a biz because 99% of my fellow countrypersons just don't get it that you can do anything energy related unless it involves petroeum products or nuclear fission. And they also believe insulation has no real value of note, that it isn't as cost effective as just paying more for natga/propane/electric/burning more wood, etc. You can't commute to work unless you have a 500 HP or larger car or truck capable of 150 MPH, etc, etc.
It just got old so I quit. Had some good successes, but.....I dislike arguing stuff like that with folks. Most people are convinced in advance that solar/geothermal/wind etc just "can't work". I've seen it work well, seen solar PV work well, yet people just won't believe it. My insulation work before was jaw dropping amazing..but you can'trconvince people they can cut their heating and cooling costs down to 25% or less of what they are using now. They don't believe it. "Why aren't 'they' doing it then"? Even if you show them references and examples, it still won't stick (for most people, quite a few folks get it, and I've discussed this phenomenon with them they hear the same thing, even from friends and family who can SEE it).
*shrugs*
good luck
There's always kerosene heaters as well as your propane option. Solar heat without massive thermal mass won't work at night, so skip that.
Anyway, got the idea when some friends had a chip pile delivered and I am marvelling at all this free heat coming from the pile, nice and steady, lasts months/years until the composting is finished.
