foldable / swinging coil water heater?

Longtime reader first-time poster:

My partner and I are DIY-designing our off-grid cabin and one obvious stumbling block for lots of us is how to heat water safely, efficiently, cheaply, etc.
Researching our options I notice lots of people use propane but we'd like to avoid relying on it, so naturally instead we are looking to utilize our main source of heat: a steel wood stove. I've seen there's problems with coiling around the chimney pipe because it over-cools the internal exhaust convection, and there can be over-heating problems if the pipes are built into the stove. One instructor from Living Web Farms pointed out he just puts a big 16 gallon open-lid brewer's kettle on the cooktop of his stove and heats up directly that way. Heating like a kettle seems best because A) it's on an as-needed basis, and B) you can remove it if the water is too hot or the stove needs to heat up evenly. But it's hard for me to imagine a bulky, un-piped kettle working well for showers.

I'm throwing this out there because I haven't seen anyone else do this before. Some folks use expensive water "jackets" externally mounted onto the back or side of the firebox stove, and others rig up a kind of "serpentine" panel of copper piping (like the one in the picture below) for the water to flow across as much surface area as possible to mimic a jacket but maintain continual flow.

What I've considered doing is basically using the latter design, enclosing the pipes in a heat-conductive panel on a hinge (or two) and just using flexible, heat-resistant, corrugated stainless steel hoses for both the inlet and outlet ends of the otherwise copper loop attached to a storage tank. I might keep the tank on the other side of the wall behind where the stove is, so if the fire is going all day but the finite water in the tank is hot enough we can just fold that panel 90 degrees away from the stove so that it's flat against the wall.

Does that make sense?

Welcome to Permies!

I think your idea has great merit.
You might be able to use just the corrugated stainless steel tubing, without the copper, if it comes in long enough lengths.

Welcome to Permies. I like your idea alot.

How will you get the copper coil to "swing" away from the heat source as the water approaches the boiling point in it?
How will you get the copper coil to "swing" towards the heat source as the water in it cools?
What will happen when/if there is some swinging malfunction and the water in the coil overheats and turns in to a vapor (.... explode)?
How many swings will it take for the "hinges" to break/malfunction?
How do you make it fail gracefully aka without damage to the house?

How will you get the hot water that is in the coil to your storage?
Will you run the system continiously to provide radiant infloor heating?
Or will you only use the system to intermittently charge up a 40-80gal hot water tank for showers/etc?
Will you stratify the water in the hot water tank? How will you heat the DHW tank in the summer?

Thanks Bronson, maybe I will.  The basic idea might have partially come from steel sprayer hoses you find in the dish pit if you ever worked in a restaurant. I guess as long as I'm able to get a very high heat approved hose AND if the rest of the system is designed competently, it should work.

Bengi, I'll try to answer everything. I think the first two lines of questioning might mistake my design. At any rate it's not supposed to swing itself like a thermostat. The idea would involve sturdy hinges anchored to the (likely brick) heat shield wall behind the stove, on a protruding part of the wall that gives it clearance to swing like a small fence gate and lay flat against the wall simply. The reason I say the heat shield can protrude is it might be built as a partial enclosure around the back corners, for thermal mass as well as a safety barrier for foot traffic around a nearby door. The hole through which these hoses pass would be part of the design of this shielding. The panel would swing by hand, and if it is in use there will be at least one thermometer we can monitor, along with a pressure relief valve (with drainage). As a passive system I would assume the water temperature in the tank maintains its own stratification.

"How do you make it fail gracefully?" is going to be one of my new favorite phrases so thank you for that. In this case I would hope enough of the pipe is corrugated and/or otherwise flexible, so if the hinges busted out from the mortar or something I'd hope it would have enough slack to fall a few inches to the ground. As for steam explosions, with temperature gauges and a relief valve on my side I'd hope it never gets close to that point before I could just swing it back to the off position.

The water would be set up the way most passive heating works, with a cold intake on the lower edge of the "door" or panel, and the heat exit end of the pipe on top, going through the (in operation, straightened) flexible tubing going up at an angle to a storage tank on the other side of the wall. This will be our ersatz "laundry room" type space in one way or another. Floor heating would require a separate setup I think, and this will be a small 20x20ish space (to start with anyway). Whether we manage to rough it by using wood for all our cooking, or if we stock up propane for a burner stove, that's probably going to be the bigger question for hot water in summer.

Wetback water heating systems are common here and they are painfully simple. There is a heat exchanger in the firebox, usually in the back or above the baffle, and this is plumbed in as a loop to the hot water cylinder (atmospheric pressure with a vent to the outside, usually through the roof). The hot water tank needs to be higher than the wetback for the thermosyphon to function, but apart from that there is almost nothing that can go wrong aside from leaks.

Examples

Here's a bolt-on unit that goes on the outside:

Side mount

The internal ones suck a lot of heat out of the combustion chamber and can result in an inefficient burn, and for this reason we can't install them in urban areas. But that second example is along the lines of what you're proposing.