Jan Boer

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!

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!

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 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.

Thank you Phil and Tristan!
I've started another thread as suggested.
The answers to your suggestions and extra information has been added there.
I hope you can find the thread, the header is: "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.

Glenn Herbert wrote:Cob from local clay may be able to stand lower ranges of RMH riser use depending on the locality. Mine fires hard and strong at around 1800F, shrinks and distorts some as it vitrifies around 2000F, and melts by 2300F. Clay in traditional stoneware pottery regions can be good straight from the ground to 2300-2400F, maybe more (that is the temperature the pottery is fired to while remaining perfect.) If your local clay is silty or has other drawbacks, it may not even be good to 1800F.

Hey, this is my first message here. I'd like to thank you for all the detailed contributions you've made so far!

The idea to built a heater so sufficient, low cost and kind on wood is very appealing.  Especially as I would like to extend this blessing to poor Lebanese and the Syrian refugees, who are burning plastic, clothing and black motor oil...

Limitations are therefor money in general. Also, everything is built with 4inch / 10cm pipes. Those are openings in the wall of apartment buildings to which diesel heaters or wood heaters are attached.

So, I'm looking to built a prototype 4inch system, little mass to prevent draft problems.

Since those can't get really hot it seems, a cheap cob riser would suffice?
How would I insulate the riser however? Since I don't want to use ceramic wool (maybe hard to get here, possibly toxic and expensive for locals).
Same goes for the burn chamber, it should be insulated to get to high temperatures.
Basically I'm wondering if I can get away with mostly using cob and still get that second burn.
I will inquire about what local pizza bakers use and how hot it gets in those ovens.

It would be amazing if poor people would be able to use twigs to heat their homes!!!