Looking for a giant Kelly Kettle

I am looking for some help in locating something that I can repurpose.   I have been working on building a wood fired hot tub.  I have a coil of copper around a rocket stove and it is working but it is not very efficient.  I spent 2 weeks using a "Kelly Kettle" on a wilderness expedition and I am not convinced that this would be a better solution to heating the water.  I basically need a double walled chamber with an intake and outflow for the chimney.  I am looking for ideas for something I can find in a scrap yard or somewhere that would work like this but so far I am coming up blank.  I thought I would reach out to the brilliant minds on Permies for some thoughts and direction before I look into getting it custom fabricated.  

Thank you for your time.

Brayden

A gas fired water heater tank fits your description.
Around here they can be had for cheap or even free.
I have used one in my own boiler design.
One challenge with using one with a rocket stove is the width of the interior chimney and the height of the tank.

I have also created a  this kind of water jacket from scratch.
The inner cylinder/flue pipe is set in water stop concrete inside of a larger outer cylinder.
The concrete is sealed with a silicone caulk/acetone mix.
Because the chamber is always filled with water, high temperature refractory materials are not needed.

Fantastic input.  Thank you Willam.  I will start exploring those options

Brayden Plummer wrote:I spent 2 weeks using a "Kelly Kettle" on a wilderness expedition and I am not convinced that this would be a better solution to heating the water.

Hi Brayden, I'm assuming this is just a typo? Makes it a bit confusing to understand what you are actually looking for though...

A picture or sketch of your setup would be super helpful.

If you have the rocket stove already laying around, and the copper pipe, have you tried putting the coil inside the riser? Or cobbing around the copper coil and riser, so that theres more surface area for heat transmission?




Also consider moving the thread to "hot Water" or "wood stove" as it's not really rocket oven related.

I was gifted two coal fired cast iron water heaters. Maybe something like that? The r2d2 top separates from the base.

I have some photos of my boiler build on this permies thread:
TLUD fired outdoor boiler

Inside of my TLUd fired Boiler, showing 2 gallons of water and the central flue

Here is a simple cross sectional diagram of the kind of water   heater I used:


The next time I build one of these I will leave the tank and insulation mostly intact, and build a fire chamber beneath it.
They are well set up to absorb and retain heat from "clean" exhaust gasses, and most of what I did made that worse.
A full tank will moderate temperatures to no more than 212°F, protecting the metal and insulation of the tank.
I will remove the pressure relief valve and replace it with open pipe that vents to a safe place- no steam bombs for me!


In my experience, tanks that leak at normal water pressure will not leak in any detectible way under low/ no pressure setups, so I wouldn't even worry about that issue very much, especially if you are using it outdoors.
On a similar note, I used to wonder how people were using PEX to plumb boilers, since  most PEX is just rated for 200°F, but it turns out that rating is for 80 psi.
The temperature rating on that same PEX goes down with higher psi's , and it is more resilient at lower psi's
Most boilers regulate their temperatures to below 212°F and  run at lower PSIs, so they have more margin for error.
That said, the corrugated stainless hose usually used for natural gas can be used for liquids instead, and it can deal with  212°F, no problem.
I'm liable to use  it as the pressure relief pipe  on any future boilers, as it is very competitive with copper prices and easier to install.

I know you are looking for a DIY, but maybe some info about these large Thermette's (New Zealand version of a Kelly Kettle) might help with some inspiriation. A friend of mine has a 5 gallon one, loves it for base camping.  
https://spiroloc.co.nz/product-category/wood-fired-boilers/

They also make a wood-fired water heater:  https://spiroloc.co.nz/product-category/wood-fired-water-heaters/

I look forward to seeing what you end up making.

Thank you all so much for the input.  I have a great deal to mull over now and work on over the winter in my shop.  

The old way in the UK of heating water from coal fires was known as a "back boiler" . Maybe if you look up how they worked, you might find some more ideas perhaps applicable to a wood fired option?

I expect you have in mind a fancier solution, but our hot tub is two cast iron bathtubs outside, with a pit dug under them. bit of a box around the exposed part of the pit. The bathtubs were free. My husband didn't want to breathe smoke so he rigged it so the smoke crosses under both tubs and then up a chimney made of some sandstone blocks (which were also free). The tubs are plumbed together to equalize water temperature but we often use buckets for that purpose too. Simple and pleasant. We got 2" thick covers from the local "rubber" factory (actually engineered foam)--these are heavy enough to rarely blow off, and keep debris out of the tubs and keep the warmth in overnight if we feed the fire a bit before going to bed.

Not a diy, but we love our chofu.
https://islandhottub.com/wood-fired-heater/
Thought of diy-ing copper tubing around a firepit, but the location is too close to the house for me to be comfortable.

Chofu is a wood fired hot water heater.  We use the prunings from the yard to heat the water to soak in the tub and make charcoal to throw in the chicken and goat pens to become inoculated as biochar to use in the garden.  I have difficulty breathing any time I get into a chlorinated pool of water and it gives me itchy skin.  So I was glad when Frazer Mann of Island Hot Tub educated us about Hydrogen Peroxide.  With the Chofu, there is no motor noise (works by thermosiphon) or bubbles.  Just a nice warm quiet peaceful soak under the stars.  Our tub is just a deep bath tub I got off craigslist….Frazer was super helpful when educating us just where to cut the out and intake holes in the side of our tub.  Very promptly responsive to any questions I sent by email.  When we empty the tub, it runs into the swale that waters the front garden.  Peroxide is safe for the yard (what is left of it by the time it leaves the tub).

This style of woodburning hot water system is quite common in rural Bulgaria, especially outdoor bathrooms or off-grid properties: https://www.ebay.co.uk/itm/252418071520   We don't have one, though I'm considering it if I do a full outside bathroom, but as far as I know it works very like a Kelly Kettle. There's a firebox at the bottom, the chimney passes through the middle of a water jacket, cold water goes in at the bottom, hot water comes out at the top.

Jane, that water heater is impressive!
I wish they were common here.

Yes, apparently they're very efficient! Hubby wanted one in our indoor shower room, but it wasn't going to fit, plus the builder had already closed off the chimney there. But when I do the outside bathroom, I hope to include one. It heats the shower area as well as the water!

carla murphy wrote:Not a diy, but we love our chofu.
[...]
When we empty the tub, it runs into the swale that waters the front garden.

That looks like a nifty little unit, carla! Thanks for sharing the link, I enjoyed reading that site.

About how long would you say it takes to heat your tub?
And how frequently do you drain/refill it?

Jane Mulberry wrote:This style of woodburning hot water system is quite common in rural Bulgaria, especially outdoor bathrooms or off-grid properties: https://www.ebay.co.uk/itm/252418071520

Jane this is really cool!
Echoing William, I wish I could pick one up locally.

I found the brickwork inside fascinating and wanted to make sure it wasn't lost to the wiles of the internet - I'm attaching my favorites here to preserve and keep the ideas flowing!