Ferrocement Rocket Stove Water Heater & Cistern idea

Hey All! I am relatively new to rocket stoves, but have been getting more and more curious about them for our needs and future builds here in coastal B.C. Canada. And I had an idea for a ferrocement version of this rocket stove here that was made in Quebec;     As we are lacking in natural clay deposits on our island for cob works.

I was thinking of using single walled large diameter chimney pipes for the mold for the wire work, which I would bend around the chimney and j-clip to itself, and then fit, trim & J-clip the wire-work together to make the rocket stove similar to the one in the video above. And I am just wondering, feel free to chime in, what dimensions/heights I should shoot for? The single walled chimney comes in 5", 6", 7",and 8" diameters and various heights, and I am wondering what ratios I should use for the ferrocement feed chamber, and exhaust chimney, keeping in mind this build is very simple (in theory).. My main thoughts are I need to be able to fit my hand into the feed chamber, and exhaust so that I can ferrocement the inside of the rocket stove. I also had the idea of leaving the single walled chimney parts inside the rocket stove to better protect the concrete..

And speaking of protecting the concrete, I was thinking of doing a ferrocement mortar mix of 2 parts sand, 1 part fireclay, and 1 part portland concrete. With added perlite as I heard that helps? (Why does it?) And my usual added Admix, and rice hulls for strength. Any thoughts on this increasing it's heat tolerance levels?

As well my long term plan is to plumb it into our bush bath, and to build a raised ferrocement cistern with shower head attachment, and the copper hose intakes/plumbing on both bath and raised cistern. My plan is to make a wire-work mold of one of our plastic water barrels that has holes in it, and make wire-wrapped rebar stilts/framework to lift it up (plus a ladder), attached to the cistern mold, then ferrocement that bad boy and set her up. So that the cistern is raised up high for gravity fed hot showers. The rocket stove in theory would have two copper coils, with cold water shut off valves, so it could heat the bath or shower, or both interchangeably. Just fill and heat!

So what do you all think? Is it feasible? Do you have any advice?

Thank you,

Mogi of the isles.

P.s I am using the book "Fantastical Ferrocement" as a guide for all my ferrocement works. And have a book on ferrocement cisterns coming in the mail to help with that aspect of the build.

There is one major catch here.  Cement is not high enough temperature.  At about 1000 degrees F cement breaks down.  Rocket stoves can potentially reach twice that.  So you will need high temperature furnace cement and not standard portland cement.

Thank you for the response!

So something like this; https://www.homehardware.ca/en/hi-temp-stove-furnace-cement-946-ml-grey/p/2045129

I was hoping to work around this issue with the added fireclay & perlite into the mortar mix, but I don't see why I couldn't do both your suggestion and that. At least with the Ferrocement mortar, I would be using only 1 part of the mix ratios for the furnace cement additive. Which could cut down on the costs of it. And it is doable as it would be a smaller build rocket stove. But is it feasible? I wonder how much mortar I would need per rocket stove. But it would only be the rocket stove that would need this special treatment, the ferrocement water cistern would never reach that heat range. I should price it out a bit I think.

Any suggestions on the ratio's on the schematics of the rocket stove itself? I am very new to Rocket stoves, so don't know the general guidelines yet. I ordered the book "The Rocket Mass Heater Builder's Guide", So hopefully I can glean some useful info from there too once it comes in the mail. All the best from your friends up North, and thank you again for your suggestion, I hadn't thought of that.

Yes something like that will work fine.  Suggest shopping around on price though.  As there should be cheaper answers for similar products.


As for ferrocrete I have not played with it but have been studying using basalt rebar products instead steel that can be used for canal projects and the same reasons would apply to a cistern  The mesh looks like the core start product and the concrete dome home makers are apparently using basalt roving or basalt rope.  basalt products.  check out the mesh, roving , rope product since I can't link directly to them.

The most basic format for a high performance rocket stove is a J configuration, there are known dimensions that work very well and have been tried and tested over many years.
It is fun to experiment but I would advise sticking to the known parameters for your first stove.
Regarding suitable materials, you have to consider a few things…generally speaking  you want to use high temp refractory materials  but also you need to understand about rapid heat and the effects of expansion and contraction.
Then you need to think about insulation, in order to get the stove hot enough to burn off the smoke, you need to stop the heat escaping before it has done its job.
So start studying J tube designs and building materials, there are lots of great build threads on the forum.
The most popular size is 6” but 5”” will work and even 4” is possible for some applications.
Note … perlite does indeed have its use as does vermiculite but, its addition to any cement mix will severely weaken the mix, so you need to study that aspect as well.

Hi Mogi,
I agree with Fox sending you in the direction of J-Tube rockets, especially if it’s going to be a long term installation, as your warm water setup sounds like.
A word of caution: Please be very careful with wood fired devices and pressurized warm water systems. Without proper safety in place the system can overheat and basically explode from the pressure build up. It’s called the boom squish around here and is known to be quite devastating.
Best way around it is an open system. For example heating a large container of water (that isn’t completely closed, so steam can escape). And then you run copper pipes for your devices through that big pot of (almost boiling) water.
That would also work with the 2 different sistema you mention, one for shower, one for the bath.

The Y-shaped rocket you show is common as a cooking stove, where the purpose is to get a lot of heat out of the top, but that is not helpful when you want a lot of heat in the riser surround.

A J-tube as Fox describes would work better. A 4" system, even if it works reliably, will need to be fed very frequently. A 6" J can hold more than twice as much fuel and will burn more steadily and longer. For your idea of wrapping copper coils around the riser, you will get much more heating by making the riser very tall and spreading the coils over the full height. For the much safer plan of heating a large vat of water with coils submerged in it, you would want the riser to be the standard proportional height, with an expanded skirt above that to enclose the whole vat for maximum heat transfer and avoiding radiant cooling from exposed sides.

The purpose of perlite in a mix is to add insulation and reduce heat loss from the sides of the core, keeping the fire hotter and more efficient.