Rocket Oven with Water Heater Coil

Hi to forum community from a relative newbe rocket stove / rock mass heater explorer, I was wondering if anyone has any experience with combing a rocket stove or mass heater with a copper coil in the flue stack for connection to a convection circulation water heater, the idea being that the rocket stove also provides hot water while running or also possibly heats a room that is remote from the stove by siting the cylinder in that part of the building. From what little I do know the flue tube can reach over 2000'F and its accepted wisdom to not place metal within the flue tube section of the rocket stove. However given the copper coil would be filled with a water and embedded in a clay perlite  stack, as long as water continues to circulate via convection the 1984'F melting point of copper should never be reached. My questions has anyone got experience with such and system ? and could this have any detrimental affect on the rocket stove's ability to burn off build up within flue which is a key aspect of of the the rocket mass heater or stove ?

For anyone who can contribute to this subject thanks in advance.

Ian    

Hi Ian.

The accepted wisdom suggests that we don't know enough about how this would work over the long-haul. Also, if there were to be some kind of restriction within the coil at any point in its life, you could be looking at a rocket-oven-powered steam and masonry bomb. Boomsquish, as it's colloquially known.

Domestic hot water doesn't need to get as hot as the burn tunnel of an RMH or rocket oven. There's no call for doing it that way, considering the risk.

I think it's overkill. For comparison, look at the operational temperatures of on-demand tankless gas water heaters and the length of the heat exchanger through which the water passes to get heated.

I would park an open tank atop an RMH's riser, and plumb it to my hot water from there. No boomsquish, no accidental self-flash-steaming, just lots of near-boiling water, ready for use.

This is not to say I wouldn't like to hear more, just that I think that the possibility of boomsquish is too high as compared to more straightforward methods of water heating.

But let us know how you decide to proceed, and good luck.

-CK

Hi Ian;   Welcome to Permies!
And Welcome to the wonderful world of rocket science as well!
There is a lot of information to absorb.

Lots of folks have wanted to try heating water.  There are ways to do so...
BUT there are ways to get hurt trying it as well!
We call it BOOM SQUISH, water instantly vaporizing to steam ... you don't want to be there.

We always recommend, building a few regular RMH's before trying a more technical build.
Have you got a copy of the RMH builders guide ? Readily available on Amazon.
It is invaluable in the proper construction of an RMH.

Pop on over to the RMH forum and read all about rockets!
We will start turning you into a Rocket Scientist!

thomas rubino wrote:Hi Ian;   Welcome to Permies!
And Welcome to the wonderful world of rocket science as well!
There is a lot of information to absorb.

Lots of folks have wanted to try heating water.  There are ways to do so...
BUT there are ways to get hurt trying it as well!
We call it BOOM SQUISH, water instantly vaporizing to steam ... you don't want to be there.

We always recommend, building a few regular RMH's before trying a more technical build.
Have you got a copy of the RMH builders guide ? Readily available on Amazon.
It is invaluable in the proper construction of an RMH.

Pop on over to the RMH forum and read all about rockets!
We will start turning you into a Rocket Scientist!

I understand instant vaporization in high temperature system, boom squish as you call it, this can happen at ambient temperatures also in negative pressure circumstances known as water knock (damaging pump impellers in water systems), are there any recorded instances of this in a rocket mass heater or stove to refer to ? the reason to exploring this further is that as it is a open loop in order to create a circumstance where pressurization could happen two blockages would be required, one before and one after the coil, if either side of the loop where open then steam generated would push pressure back to the tank which is not sealed. More likely circumstance is the coil is allowed to boil dry and then the copper coil would simply melt. In terms of building systems I am researching multiple designs from very simple rocket stoves and mass heaters to more complex systems as I may have an opportunity to build these units commercially in Africa, it would however make the commercial aspect a great deal easier if the system could provide cooking, heating, refrigeration and hot water. The environmental advantage of a rocket system over charcoal burning which is the current standard is unlikely to open many wallets, the low fuel requirement and options to provide hot water, oven and even absorption refrigeration combination would be much more of a motivation to people. Unfortunately I do not know of much uptake other than wood burner pizza style ovens which take patients to use (pre-heat and wait for embers ect). If boom squish is an unavoidable problem then placing a larger coil in a lower temperature section of the system (inside the thermal mass section for instance) and or perhaps including a pressure relief value maybe a way to go, are there any known examples of this ?  

Hi Ian;
Here is a link to an awesome safe rocket water heater  https://permaculturenews.org/2012/11/23/rocket-stove-hot-water/
Here is another https://permies.com/t/93770/Hot-Water-rocket-stove

Yes as a preheater for standard hot water. pipes thru the mass can be used .
Suspending an open tank over the barrel on a standard rmh will provide safe water heating as well.

You are correct, in that only under certain conditions could Boom Squish take place. In this case with open publication, I prefer to error on the side of caution.

Sounds like you are working on an interesting project.  We would love to hear more about it as you get started.