tiny house rocket mass heater: the cyclone batch style

I don't understand how normal bricks are able to withstand the heat. Aren't refractory bricks necessary? What temperatures are reached inside the bell? I'd love to build this in my tinyhouse.

Kirk Mobert wrote:The mortar is clay/sand, again using locally sourced clay soil for the clay and locally sourced sand too. Cement based mixes can't handle the heat and should NEVER be used in stoves.
The plywood form is for making the arches. The bricks are laid over the form and then it's taken down and moved for the next row.

Old school bricks made from clay will do quite well.

And what about the mortar?

paul wheaton wrote:Old school bricks made from clay will do quite well.

I think a sort of cob is used as mortar.

Mjølner Rankenberg wrote:And what about the mortar?

For my own brick bell I've used a fireclay/fine sand mix with a 'very' small amount of Portland cement to help hold things together while it dried properly. It's working well so far.

this is so awesome kirk! brilliant. i mean, donkey....never got used to calling you that, but funny thing is that's also my nickname now at Itazipco healing camp in South Dakota. you might not remember me, but im the guy from kenya who used to run in the mornings that was at one of your workshops a couple years back.

using some of the ideas gleaned here, i will soon be setting up a tipi on a raised platform with a batch box rmh...had already done one, but it was temporary, with a converted hq wood stove (ash/cob insulated) as the batch box. worked great, but the tipi cover itself had some issues...getting a new one and am now re-vamping the whole project - came on here for some inspiration and found the "rmh in a tipi" thread(!!!)...so awesome Paul Wheaton and others. Thank-you all for sharing your beautiful work!

really hope you're still watching this thread as im curious about the ratios of cow dung, grog, ash, and clay soil...knowing that i'll have to play around with whatever mix i make for the best results. And also...i saw it asked and answered, but the primary and secondary air is not clear to me with the casserole door. Is there a gap somewhere between the glass/pyrex door and the cob that allows air in? I think i see one at the bottom of the door in the pictures/videos, but im not sure, and am also curious about the dimensions - doesn't seem like it's quite up to peterberg's csa dimensions for batch air intake - but please do enlighten me. and is the metal channel to the throat running over the batch box then down into the port like a typical peter channel?

[quote=Kirk Mobert

I think that because my mix is really light (wood ash and all) it insulates well, which helps get the temps up. The other important detail is undersized bell leading to a hot chimney (not too hot, you'd have to work hard to get burned on it).

....The firebox mix is intended to be able to make anyplace in the world, by the poorest people.

Kirk,
thank you for sharing the wonderful pictures and details!  When you say the mix was really light (wood ash and all)...are you talking about just the mix on the inside of the rise, correct?  is there any information on making and applying your own refractory mixes on these forums?
also, when you say the firebox mix is intended to be able to make anyplace in the world...what do you mean by 'firebox mix'?

thank you!

Wonderful

This is really great. I really like this design and am wondering if there are plans so that I could build one? Thanks

I agree way cool!

Hi I am a new be to this site i have 2 question.  How do you remove the forms in arch with damaging the structure. With the bell heat exchanger do you need to periodically clean out ash build up and if so how would this be done.

Love the brilliance of your design so simple and elegant.

Thanks
Andrew
Lower Creek
Australia

Andrew, often the forms are juste burned, ans yes you need to clean fly ash. Often you make a removable top, or a cleanout door

This looks like the ideal option for our situation. Since there is apparently no plans available for this build, is there anyone willing to help guide us through this process? We've ordered and read Ernie & Erica's book, also Ivanto's (sp?). However, since we've never built one, we feel more comfortable having someone to communicate with throughout the process. Funds are our largest lacking resource and wasting money and materials is not an option. We are in Arkansas with access to local clay and sand on our property. Knowing how to mix this for mortar is something we would need help with as well. We do have a nearby friend who has built a RMH in his home and is willing to help periodically, as time may allow and this may be minimal. We certainly appreciate anyone willing to help. After our first build, we have 5 more to build in the cabins on the property. Thank you in advance.

Hi Karlene;  Welcome to Permies!
That particular stove was built by "Donkey" He has his own forum, known as Donkey proboard  Here is a link http://donkey32.proboards.com/ Anybody, including donkey, at that forum would be glad to help.
Also lots of experienced builders here at permies will be happy to share what they have learned.
As a first time builder, rather than a batch box you might start with a J tube rocket.   It does not have to use a long heavy mass it can also be plumbed into brick bells.
Just being able to see your neighbors rmh should help no matter his style of build.
Making cob is work no getting away from it.  But if you are containing that cob within walls then its consistency becomes much less important. Only exposed cob benches need smooth crack free cob . If your mass (if you use one) is contained by brick or stone then the cob is just filler around your rocks.  

There are several of us here who would be happy to advise in a forum thread, so that the information is preserved for future readers.

I think if you start a new thread with your site information, you will get good detailed direction. This original thread has a lot of good information for those who can look at photos and figure out brick layouts, etc.

Thank you, Thomas and Glenn, for your helpful responses. I will follow up with your suggestions. We're off-grid and rural with a once-a-week town trip to the library to gather information to digest and process at home. This week we were blessed with two trips in one week! We very much appreciate your help in directing us in how to best proceed. We'll post to share our progress and questions along the way.

This design is thrilling!

I want to start building one!

I am living in a 20' bell tent in the woods, and I wanted to figure out a way to build a rocket stove that would be small enough to pick up and move (with a forklift or the like) and this totally fits the bill! The only problem is the height-- my tent has limited headroom, being conical in shape, and a bench would've fit nicely closer to the wall. But a 6" system would be overkill and too heavy. I think I can figure out how to make this one work, though the placement will be awkward.

I wonder if I can get it built fast enough to use yet this winter? I do NOT want to shell out hundreds of dollars for a conventional wood stove that'll be all smokey and not provide any heat through the night, but while I'm building a stove I'll be real cold till it's done... and do I build it IN the tent, or outside the tent and test it and THEN bring it in? I think I'll try building the base, the firebox, and the lifter outside (I want to see if I can tweak the port shape to get the double rams horns, which will be interesting since the design is asymmetrical!) then bring it into the tent and finish building the bell over top where I can stay dry. I'll need to decide where to put the stove jack in my tent roof for the chimney. Oh my!

Started myself a thread for the project! https://permies.com/t/99010/Building-tiny-RMH-tent-woods

I say this with the utmost respect for those who built it, especially since it was produced out of materials ready available in less-advantage areas of the world, but isn't this just a really small masonry heater?  Not that there is anything wrong with a small masonry heater.  In fact, I think this is a good case study in just how small a "mass heater" can be and still be effective.  It is also quite pleasing, aesthetically, which is a difficult thing to say about many of the "barrel and pebbles" RMH designs.

It just seems to me that we have come full circle, in that we are rediscovering the effectiveness of the various masonry heaters that have built throughout the colder regions of Europe and Asia for centuries.

To some extent, yes, this is a continuation of a centuries old tradition... the difference being the innovation of a complete combustion firebox that gets more heat and less pollution out of the same quantity of wood. Bringing that back to the familiar and esthetically pleasing forms of the past is a reasonable development.

RMH

I want to build one of these, but I feel quite inadequate to do so.
Donkey, I see that you are doing a "master" class on all things rocket. That's way more than I need. If you ever do a class on building THIS heater, I want to come! Bonus for me if it's in Coquille, a couple hours from me.

This is amazing!!! Thank you!! Question. Sorry if I didn’t see it in the thread. About how much did this cost you to build?

Hi Stephanie ;   I'm sure that most of the materials were used and already on site.  So no hard number would be mentioned.  

I'm guessing, that even with brand new bricks, clay , refractory and pipe it would be less than $500. Could be a lot less with used bricks , pipe.

the cyclone gets a little surgery!  (in three parts)


Diagnose and begin the cutting




Rebuild the riser




Replace the bricks, plaster and then test

Thank you for part 1 of the surgery video....I sure hope the patient lives! Its got the makings for a great soap opera.
Could it be that the dissimilar materials between the perlite/clay riser and the neolithic refractory is causing expansion/contraction to slowly crumble away the connection? Wondering if a buffer may help like a thin piece of ceramic fiber blanket to cushion the movement?
Also, now that the side is all open, if a clean out /inspection port would be a good addition here? Looking forward to part 2.

I added the new videos to the post a coupla posts back.

josiah's artwork after it was all put back together:



taken from josiah's bootcamp thread.

Lessons:

1:  for a batch box rocket mass heater, make sure that the riser slot is taller than the wood feed. Or else smoke will come out the front. And smoke out the front is utterly unacceptable.

2:  As matt walker mentions:  no matter what glass you use, the casserole lids break.  I suspect that the glass that is for electric stove tops might work, but they don't come in the casserole lid shape.  So it may be possible that something could be cobbled together.  So we went with a cast iron skillet as a door.

3: We know that firebrick doesn't have enough insulation to be a riser, which is why one riser design is to wrap durablanket around standard firebrick.   We are beginning to learn that the orange firebrick (insulated firebrick) is better, but not much better.  

4: For most of the burn of this, there would be smoke.  That is absolutely unacceptable.  



So we solved #2.   And for #1, #3 and #4 we had plans on things we could do to fix it ....   but ....


5:  A normal rocket mass heater in this space would probably make the space quite comfortable in about ten minutes.   And really warm on a really cold day in about 20 minutes.   But this rocket mass heater had no barrel for "quick heat".   So it would often times take three hours to to get the space comfortable.   And since it is a batch box, it was a lot of wood.  And then after a long three hours, people would go to bed only to wake up an hour later to find themselves in a sauna.  They would open the window so it could cool a bit so they could get back to sleep.  And then wake up to a cold cabin.  This is absolutely unacceptable.  


All of our ideas to solve #5 were weak and probably would not help enough


Since this rocket mass heater is so beautiful, we had very long discussions about ways to save it.  But in the end, we made the difficult decision:  it is time to replace it.   On august 26th, 2020 it was removed.


A pebble style, j-tube, 4-inch rocket mass heater is going in:



(pic from Dez's thread)

The pebble mass will be partly a bench and partly under the bed.

So I'm hearing that this is the thing many people have been waiting for--the Renter's Rocket.  

A). It is small, takes up only a few square feet of floor space
B) It weighs less than 2,000 lbs.
C) the materials are pretty cheap (Paul said about $200 in the Uncle Mud podcast, podcasts #382-4)
D) It can qualify as a masonry heater, so you would not be required to have the chimney exit temperature.  
E) a fair portion of renters rent rooms in a house, or a floor of a house, that has an existing chimney and fireplace that was filled in with drywall a while ago, but this could be opened up again.
F) Many renters will come home in the evening and have dinner indoors, vs. just coming back to the cabin shortly before bedtime.  You'd have time to get your heat up to temperature.  You could use an electric heat pad for the meantime while eating dinner and such.  You could work around the no-quick-heat problem.  You could cook on a lightweight rocket _stove_ that would heat up your space, if codes allow that, or use a code-approved wood stove instead.

Is this accurate?
Most importantly, item B, is 2,000 lbs a normal load for the 2nd floor of an old house? 3rd floor?  It's the equivalent of two heavy upright pianos fit into a smaller footprint than one piano.

Also, any updates on how this cyclone rocket performed with the test of time a year _after the surgery_ or with a rebuild elsewhere? did it still have any other issues with items 1-4 after those things were addressed?

Regarding #4, the smoke-back was how it functioned before the surgery?

paul wheaton wrote:Lessons:

1:  for a batch box rocket mass heater, make sure that the riser slot is taller than the wood feed. Or else smoke will come out the front. And smoke out the front is utterly unacceptable.

2:  As matt walker mentions:  no matter what glass you use, the casserole lids break.  I suspect that the glass that is for electric stove tops might work, but they don't come in the casserole lid shape.  So it may be possible that something could be cobbled together.  So we went with a cast iron skillet as a door.

3: We know that firebrick doesn't have enough insulation to be a riser, which is why one riser design is to wrap durablanket around standard firebrick.   We are beginning to learn that the orange firebrick (insulated firebrick) is better, but not much better.  

4: For most of the burn of this, there would be smoke.  That is absolutely unacceptable.  



So we solved #2.   And for #1, #3 and #4 we had plans on things we could do to fix it ....   but ....


5:  A normal rocket mass heater in this space would probably make the space quite comfortable in about ten minutes.   And really warm on a really cold day in about 20 minutes.   But this rocket mass heater had no barrel for "quick heat".   So it would often times take three hours to to get the space comfortable.   And since it is a batch box, it was a lot of wood.  And then after a long three hours, people would go to bed only to wake up an hour later to find themselves in a sauna.  They would open the window so it could cool a bit so they could get back to sleep.  And then wake up to a cold cabin.  This is absolutely unacceptable.  


All of our ideas to solve #5 were weak and probably would not help enough


Since this rocket mass heater is so beautiful, we had very long discussions about ways to save it.  But in the end, we made the difficult decision:  it is time to replace it.   On august 26th, 2020 it was removed.


A pebble style, j-tube, 4-inch rocket mass heater is going in:



(pic from Dez's thread)

The pebble mass will be partly a bench and partly under the bed.

This may be a silly question but I'm all new to RMHs and would like very much to understand them so I can build one. Why is creosote not a problem if most of the heat is extracted before it exits the heater?

Hi Carmen;
If properly built, a rocket mass heater is running 90-95% efficiently.
In a J tube rocket, riser temps are 1800F. In a batchbox rocket the temps are over 2000F.
All particulates are burned, only light fly ash makes it out of the riser and into the bench portion of your stove.

I had an 8" J tube in our greenhouse for 7 years, I've replaced it with a 6" batchbox for the last 3 years.
Never in 10 years have I had ANY creosote build-up at all!
Meanwhile, I have a standard wood stove in our cabin.
I have no choice but to clean the cap area 2-3 times a season as creosote will completely block it off if I do not.

A poorly built RMH that is not built to specifications will still not create creosote, but it will completely fill your piped mass with fly ash!
When /IF that happens your stove will start lighting hard and wanting to smoke out your home.