Possible good water heater design to use wrapped around the barrel portion

First time poster.

Hopefully this is well received.

I am starting my own RMH build in a little while and was thinking how usable would this model of a water heater be.
Wrapping the tubing around the barrel portion of th RMH.

http://permaculturenews.org/2013/05/20/how-to-build-a-rocket-stove-mass-water-heater/

From.
Mvakkilainen
FINLAND

I saw this design a few years ago and it’s a pretty good one. Thanks for posting it again. There’s a lot of ways to do hot water. This one is fairly difficult to build. It depends on so many factors. Extracting heat from the exhaust rather than the combustion chamber is a generally agreed upon principle.
Right now I’m forced to use propane on my pseudo boiler until I move somewhere I can design a wood burner or dual fuel system. Cheers

Hi Mika;  Welcome to Permies!
The video you shared is a very good way to heat hot water.
However ,you mention wrapping the barrel with copper pipes ?
That is not considered a safe way to heat water . Too much chance of turning it to flash steam in the smaller copper tubing.
We call that squish bang ... a very nasty explosion.
Follow the video that Geoff  has shared, for a safer way to have hot water.

Tell us more about your upcoming RMH build.  
If possible include photo's and or diagrams of your plans.
Do you have a copy of the RMH builders guide ?  It's highly recommended!

I agree. The design Geoff Lawton uses is pretty much the safest. Might be tricky to snake the tubing into the tank and I'm not sure what sort of fitting he uses to seal where the tuning enters and exits.
Reading the comments, it looks like Tim Baker built it. He also commented and left a link to this article, https://permaculturenews.org/2012/11/23/rocket-stove-hot-water/
In that article, he says he silver solders the copper tubing to the stainless steel tank. He also says you could use a drum/barrel and utilize the threaded bungs to use compression fittings but that the drum will rust out quick, being thin plain steel.

I always figured an old water heater tank would be what I'd use and I've yet to run across a stainless steel version. The basic water heater has a steel tank that's ceramic coated on the inside and has some sort of epoxy paint on the outside. That outside coating would burn off pretty quick and then rust pretty quick after that. I guess I won't be building one until I run across some sort of stainless steel tank. If it has threaded fittings, I'll figure out a way to seal the tubing in with fittings. If it doesn't, I'll use silver solder. I've soldered with a torch before and used to watch my dad use silver solder. Pretty much the same technique. Silver solder just requires more heat.

Yes, as mentioned that Lawton heater is fairly difficult to build and get materials for. Having a tank custom made might be best option. Yes, sizing is always crucial on things like this. Don’t advise doing it in a hurry especially if not done it before. Take you’re time and design it safely.

Hello,

The main reason i liked this build. is that if after Constructing the RMH you install the copper tubing on the outside low to medium height on the barrel. and then encase the tubing. into the structure.

I would think the temperatures would be more moderate and help keeping the loop from flash steaming.
Taking longer to heat the water but with a  larger safety margin.

From.
Mvakkilainen
"Everything and i mean everthing is Possible.
Just extremely likely"

John

> stainless steel HW tanks

There may be some "monel" tanks left to be recycled. You have to be tight with a few plumbers that replace water heaters in volume and in the older parts of large cities. Anywhere from free to $50+. You'd likely have to repair some leaks,  but maybe not.  Monel is forever metal and was used in 40gal WHs 50 years ago. Before you involve yourself with old stuff like that it would probably be best to consult welders around you and see if they can work with monel reliably. If they can and if their repairs can be done with material that will hold up like the base metal, then grabbing any monel tanks that cross your path may be worth it.  Monel  actually lived up to it's hype.

I don't know if you can find new tanks of monel for love, money or anything now. If you did, it pretty sure be priced right up there with gold.  

Rufus

I built and fired an ill-fated overly ambitious J tube rocket that used a water cooled feeding tube.
The steel inner tube ran through the middle of a terracotta flowerpot that acted as the outer tube.
Both tubes were set in refractory cement,  and the space between their surfaces was entertained with regular silicon caulk mixed with a paint thinner.

The goal was to keep tempatures down in the feed tube,  allowing me to burn longer pieces of fuel without the draft reversing.
It worked,  sorta,  but there wasn't enough water to keep the tube cool enough.
Plus, my riser had gotten wet,  so it split asunder once it got going.
You could see the fire through the cracks, baleing wire held it together.
Good times!

Anyway,  I bring this up as a possible way to make a water jacket barrel.
Inner barrel could be the top 24" of a water heater tank.
Outer barrel could be a 55 gallon steel drum.
Run self tapping screws into the space between the barrels, along their bottom edges, and pour a thick layer of fiber reinforced refractory .
Follow up with regular silicon caulk,  thinned or not.
Regular silicon caulk is fine because 212 F is well within temperature tolerances.
With a band of refractory 4" thick,  we could have a 20" band of water around the inner barrel and a 10" cylinder on top.