Rocket heater from cob and cheap insulating materials that poor Lebanese and Syrians can make

Hi everyone,

This post is about making a rocket heater (with possibly a little mass) from locally available, cheap materials, that poor people can buy and make heaters with.
Location is Lebanon in the Middle East. Most people (about 90%) are now poor (some info on this at the end of the post). People use diesel and wood to heat their homes in little cheap stoves. And the poorest burn plastic, black motor oil, shoes, clothing etc. Imagine the cost for health and environment...

I would love to build a prototype rocket heater, with a little mass, that is built from cheap local resources that will save people money and health.


Limitations
A further limitation is the size of exhaust pipes: Most houses have exhaust pipes in the walls of apartment buildings of 10 cm / 4 inch.
Hence the little mass, otherwise the draft would become a problem.
O, and people live either in houses that are not insulated, or in tents.
Minimum temperature in our house gets to be 4 degrees Celsius (39 F) in the morning, regardless if we heated our house the night before:).
Also we have to open the windows at night: they build the houses so bad that all our walls and ceiling are wet.

Local resources
Resources in Lebanon seem to be: red fire brick (weighs heavy and used in chimneys and pizza ovens), clay (red, contains iron), ‘fire earth’ (looks like coarse sand, brownish and used also for building chimneys and pizza ovens). Maybe the latter is some type of fireproof mortar. They mix it with sand and water.
And finally I’m checking out what they use for pottery as this is an old craft in Lebanon.
Technical information about what temperatures etc. are completely unavailable so far. It’s Lebanon…

Your experience can help me!
So…I’d love to hear from people having experience with 4 inch/ 10 cm rocket heaters with little or no mass that DO have that second burn.

And possible insulating materials besides ceramic wool, vermiculite and scoria. Perlite is maybe available as Turkey is close and a big producer. But haven’t found that one yet either.

Last question would be: what is the hottest it will get in a 4 inch system?

Info on Lebanon for those who like to know:)
Known widely for being little Switzerland (banking sector, mountains, beautiful) and for it’s medical sector, Lebanon has deteriorated in a third world country in a few years. Years of corruption, political deadlock, bankruptcy and an influx of Syrian refugees have devastated the country. Since the revolution of 2019 this has accelerated and now basic commodities like gas, water, bread and electricity are sometimes suddenly unavailable or scarce. There is little to no hope the situation will improve in the near future.

I thought there was a thread on here about someone who taught Africans to build rocket stoves. They used the ash of banana leaves to insulate the stoves, I believe. I will see if I can find the thread for you.

EDIT: I have found a few mentions. Building Earthen Stoves

In Haiti they build rocket stoves from mud. https://www.rechoroket.com/

Hi Jeremy,

Thank you so much for looking up this post and Haiti link. They provided me with so much information and most importantly hope that I can effectively build with a cob mix that has insulating properties. Just amazing what has been already done in poor countries. I can really recommend the Haiti link to everyone, as well as the following link: http://dancelikeanelephant.blogspot.com/search/label/clay%20and%20cow%20manure%20plaster.%20cooking%20in%20an%20earth%20oven

Detailed instructions and all cheap locally available materials. Couldn't have asked for more!

Will hopefully be able to start experimenting soon. And if it all works out I'd like to share my experiences with efficiency and durability some day.

hello , some info i read whilest looking up ideas for my own stove ,lots of stuff on the M.H.A of North America site    , for some real hands on and use of basic materials to build a working stove, Cinva Ram Earth Block Heater with Tom Trout  , and Energy Efficient Cooking and Heating Stove by Richard Jussel , hope it inspires

Since you mention a restriction of commonly used 4"/10cm holes in walls for heater exhaust, I want to mention that 4" J-tubes are smaller than the common sizes that work well in ordinary builds. 6"/15cm is the smallest reliable J-tube system size. However, a 4" batch box system scales reliably if built according to published dimensions. Batch boxes take more skill to build than J-tubes, but deliver heat faster for the same size of system.

I would not advise building a batch firebox from cob, but at least common brick if firebrick is not available. This is because the wood will be rubbing the firebox sides and cob would be damaged easily. Perlite/clay works fine for heat risers, using a sacrificial inner form which will burn out and a light sheetmetal outer form which strengthens the riser permanently. Mine on my 8" J-tube is still working in its seventh season. A 2"/5cm thickness of perlite/clay works well for me.

Hi Glenn and Tony,

These are some great ideas! I'd love to test them out soon, however time is a bit short right now and the season is not right to start building stuff.
With the snow we got everything died down (activity wise) in the parts we live in.
Just before however, I was able to find a local pottery that supplies clay mixes as well. He was quite an expert (a rare thing here) and enthusiastic about the idea of a RMH.
However, he imports everything from the States and it's super expensive. The good news: he was able to give me a number I'll try soon of a guy from Switzerland that immigrated a long time ago and makes pottery and firebricks from local clay. Very exciting stuff. He also knows his business so won't give me nonsense answers (as most people here do..).

Love the idea of a batch firebox. I read about it on https://batchrocket.eu/
A lot to think about. I think first I need to know what is available locally and rather cheaply.
Then start playing with mixes of cob.
Then build a prototype 4 inch system to see if I can get it to work.
Then see if I can adapt (for tents it's probably not allowed to build something from brick, they don't want structures that will turn in to houses).

Thanks again!

Hi all,

It's been a while, but now it seems the time to build a  4" / 10 cm batch rocket system.
Wanted to see if I got something wrong, especially regarding the intended use of wool as a isolating material and the "pottery" bricks.

Considerations:
- I want a system that is cheap to build in Lebanon, with local materials.
- Hopefully we can prevent the illegal cutting of the beautiful forests of Lebanon as is happening now because of economic hardships.
- It needs to fit the 10cm standard piping that exits via the wall. All apartments are built this way.
- Hence the batch rocket instead of RMS. See https://batchrocket.eu/en/building#dimension for used dimensions.
- Building the bell of bricks makes it very heavy. A brick of 20x10x5cm weighs 2KG.
- So I opted for a steel bell. And later adding boxes filled with sand covering the piping on the floor to add moveable mass.
- We're aming to heat a poorly isolated 35m2 room (height 280cm, top floor) to more than the 16 degrees Celcius we are now achieving with our metal stove (outside temperatures of 0 Celcius). And it takes us 4 hours to get to 16:(

Materials:
- Base: wooden pallet, on top of it a 3,5cm normal concrete layer reinforced with steel frame
(the goal is moveability, as we hopefully will move to a ground floor house in the future)
- Fire chamber and heat riser: dark orange bricks (from the same material as pottery, fired up to more than a 1.000 Celcius)
- P channel: 0.8"/2mm steel
- Isolation: sheep wool (held in place with a chicken wire frame, and then covered with 0.8"/2mm sheet metal)
- Bell: an air compressor steel 'body' of 120cmx44cm.
(At this point we want a lot of heat fast)
- Optional: a second water boiler steel body (air inflow 10-20cm higher than air out)
(To create more heat radiation while retaining the hottest air)
- Optional: 4 wooden boxes L50xW30xH30cm filled with sand through which the pipe goes before it goes up and out the chimney.
(To store heat in mass)

Measurements
- Base measure 10cm pipe x 72,34% = 7,234 (see batchrocket.eu)
- Base pallet and concrete layer 35x70cm. Height from ground 14,5cm.
- Firechamber width 14,7cm, heigth 21,7cm, length 39,9cm. Build up from bottom to top and sides with the same brick. So the flooring is not the concrete layer of the base.
- Brick size 20x10x5cm.
- P channel 1,1cmx3,67cm. Length size of fire chamber 39,9cm + 1,1 cm + down 5cm brick + down 5,8cm + overhang 1,1cm.
- Gate width 5cm, height 15,9cm, width 3,67cm.
- Heat riser: 10x10 Heigth: height of fire chamber 21,7 cm + 72 cm = 93,7cm.
- Isolation: 5 cm sheep wool.
- Bell: 120cmx44cm Sides 2mm thick, top 4mm thick. Surface area of 1,81m2 if I'm not mistaken.

Total measurements of system:
- fire chamber 35cm width  (including bricks and isolation and cover). Height 37cm.
- heat riser 30x30 cm. Height 93,7cm.
(So that's why the bell needs to be wide...is 44 cm (7cm to each side of heat riser) enough for air to flow down?)
- total weight of pallet, concrete layer, firechamber and heat riser and bell probably around 170kg max.

A 10cm system can have a maximum surface area of 2,35m2 (excluding pipe?)
So the second boiler with 1,06m2 would exceed that and kill the draft right?
Is piping also included in the 2,35m2?

Sheep wool burns at a temperature of 570 Celcius... Is the heat coming out of the heat riser hotter and would thus burn the wool, or is the 2mm steel body protection sufficient to lower the amount of heat to under 570 Celcius?
Presuming this system can generate a temperature of 700-1000 Celcius.

Can the "pottery" brick withstand the thermal shock of quickly rising temperature?

Anything fundamentally wrong with this design?

Thanks!

I haven't checked your dimensional calculations but will presume that they are correct, as long as they are based on the batchrocket.eu figures. I once made a mockup of a 4" batch box just to test a design using uncut standard firebricks, and it worked great. It would need reloading every 15-20 minutes or so, but being able to deliver lots of heat quickly, it would not need to be kept burning for a long time.

I have two concerns with your proposal. Sheep's wool is never going to work to insulate the heat riser, even if shielded from flame. It will slowly char even if it doesn't quickly combust. You need something totally noncombustible/inorganic. Something you could use would be cob with a very high proportion of grass or chaff, whatever is cheap and fine-grained, which will soon burn out leaving tiny voids in the cob. It would not be great insulation, but would work well enough without high-tech materials. A 2" thickness of perlite-clay works excellently, and 2" (5cm) of porous grass-clay should be okay. If you can get perlite, that would be a superior low-tech option to mix with clay.

In a larger system than 4", I would be afraid of the wooden pallet catching fire before long. A 4" system may be small enough that the concrete and brick layers you describe would be sufficient. I would keep an eye on it regularly and rebuild if you detect excessive heat.

I don't think pottery clay bricks would stand up to the thermal shock cycling of a firebox. Adding lots of grog would help, as in raku clay. This is one point where buying actual firebricks would be worthwhile and last much longer than any alternative.

7cm (about 3") of space between riser and bell walls should be fine for a 4" system. It would be minimal for a larger system.

The P-channel has generally been superseded by the floor channel for batch boxes. It would be simpler to make, and to replace if and when it degrades. Batchrocket.eu has information on this, and details can be found in threads here too.

I would not use added bells or piping with mass beyond the published amounts, at least until you find that the original size has extra capacity in your situation. I would put some of that mass around your main bell to store some of the heat, as a radiator of that size will throw out a lot of heat fast. Being able to add or remove units of mass from around the bell would allow you to find the sweet spot between instant heat and storage for overnight.

Thank you so much Glenn!

Though a bit disappointing my design won't work, it's good to save all that effort for a working one:)

I'll skip the pallet idea then just to be safe. And the pottery brick I'll use for heat storage then. I'll check the floor channel idea as well.
Yesterday I found perlite is being used in Lebanon for agriculture! So I'll try your cob/perlite idea.
In a previous post of yours you mention to not use cob for the firebox because of wood rubbing the sides.

Would the following work for the firebox: The outside is cob/perlite (floor, 3 walls, ceiling), while the inside floor and walls (right and left) are pottery bricks (or regular if better) that I could then easily replace if they collapse? I'm even thinking that a cracking floor won't matter if the bottom layer is 2" cob/perlite. The ash would fill the cracks and insulate it.

My hesitation towards firebricks for the firebox is that they would crack and the good, expensive ones are not available in Lebanon (Middle East).

Then all the information about making cob for a RMS/batchrocket confuse me a bit. Most people give information and then say: it's trial and error. Which I understand because clay contents vary.
In general I should be using 6 parts of perlite to clay? And then add water until the mix stays together, and if I squeeze it no water comes out of it right?
So I don't need to add sand? Because I read about quartz not being okay as they tend to crystallize or something.
However, not using sand diminishes the compressive strength a lot.
What was your solution to all this?

For further insulation of the heat riser: could I add another bigger sheet metal around the one covering the clay/perlite mix and fill that with pure perlite, or ash or something? Would that work as insulation?

What is the recommended distance from the batchrocket to the tile floor I have if I use a perlite/clay mix of 2" plus bricks as the oven floor of 2"?

Thanks again!

You mentioned that there is material people use for pizza ovens and the like; I think that would be the best material for your firebox short of "official" high-grade firebrick. Insulating cob if it is really insulative will not have a lot of strength, and the idea of lining such a container with replaceable bricks is not likely to be practical.

The method of making perlite-clay insulation that I like is to take the perlite, sift some powdered clay over it, mist with water, mix, and repeat until there is enough clay in the mix that you can make a snowball that will hold together but pop with finger pressure. This is not strong enough to make a structure without a container around it, but insulates very well. 2"/5cm of this is sufficient for a heat riser and does not need any extra insulation around it. Sand will decrease the insulation value, and given the high proportion of perlite in the mix, would make little difference to the overall strength.

Given that you cannot have a lot of mass in your current location, and you want to be able to move it eventually, and you will only have a 4" system, I think the pallet can work as long as you also put a layer of perlite-clay insulation between concrete and firebox floor. The air gap of the pallet will allow heat to escape from the bottom. Some reinforcement in the concrete could let you transfer it to a permanent foundation later. If you can make or get a sheetmetal can or box big enough for a couple inches or more of perlite-clay around the brick firebox, that would make an ideal setup. Cutting and folding sheetmetal to make a box is easy enough with tin snips and sheetmetal screws. Even large tin cans could be opened up, pieced and folded to make a good (not pretty) container.

A note on internal surface area of bells: you would basically count any horizontal ducting in with the bell wall and ceiling area in figuring ISA. Vertical chimney piping does not count.

the current cost of vermiculite and ceramic insulation is skyhigh like everything. I havent found any cheap insulation options yet..