tiny house rocket mass heater: the cyclone batch style

This is a creation of Kirk "donkey" Mobert.  It is a "cyclone batch style rocket mass heater".

Note that there is no barrel.  

Note that this is the first time ever of using the "casserole door".  

Note that the mass is upright and not a bench.

Note that the mass is a stratification chamber.

cyclone batch rocket mass heater

Some of the construction:










This is located in the red cabin.  The red cabin used to have the "minnie mouse" rocket mass heater by peter van den berg, but that got moved to the love shack and got some upgrades.

The red cabin is so poorly insulated, it would be fair to say that it is uninsulated.  If you look at the floor, you can see between the floor boards to the ground underneath the structure.  

The cyclone gives off immediate heat through the glass door, and some from the front of the top of the stratification chamber.  But most of the heat is stored in the mass and given off quite slowly.   Early reports are that it is holding heat well into the morning.   We are getting some tracking thermometers set up.  But to be so warm in the morning for a virtually uninsulated structure is HUGE!

Also, donkey did a lot of measuring.  Most of the burn was at better than 95% efficiency and the exhaust temp seems to be not exceeding 120 degrees F.

The plaster layer will be added next.

Way Cool ! I want one... Thanks for sharing Paul.

If you all post questions, I'll see if donkey can pop in and provide some answers.

Biggest question I have is , How is the  "door " sealed ? Just cob?  Is the cyclone batch build info already out there ? How is the exhaust plumbed ? Sizes ?   More pictures & more pictures , Please !!   Thank you

How is the  "door " sealed ? Just cob?

Just cob. The lid was pressed into the cob while wet, so it fits perfectly.

Is the cyclone batch build info already out there ?

The single vortex "Cyclone" was done because the bell (stratification) chamber was a bit tight and we needed to push the riser off to one side. Otherwise, it's a 4 inch Batch Box RMH, as described by Peter Van den Berg here: http://batchrocket.eu/en/

How is the exhaust plumbed ? Sizes ?

 

As with all bell (stratification) chamber systems, the exhaust is taken from the bottom of the chamber. In this way, only the coolest gases leave the system for the chimney. It's a 4 inch chimney, we used cob to make it fit.

More pictures & more pictures , Please !!

I think i should point out that the firebox of this stove is a homemade mixture that consists of crushed red brick (grog), wood ash, cow manure and locally sourced clay soil.

Here is a graph showing one burn cycle, from starting through to the fire going out and just coals in the box.

Thanks Kirk;   This is great ! Couple more questions , are the bell bricks mortared with cob or concrete ? What is the "plywood " form used for ?

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.

See more of donkey describing the cyclone heater:

Hey guys, please forgive me but how is this loaded? And it looks like it's right up against the wood wall, is that right? Does it just vent out the back at the bottom through the wall?

Jon McLain wrote:Hey guys, please forgive me but how is this loaded? And it looks like it's right up against the wood wall, is that right? Does it just vent out the back at the bottom through the wall?

It's fed down low in the front, behind the casserole lid. It's a few inches off of the wall and has an air gap underneath as well. The stove never gets hotter than you can touch.
The chimney is attached at the bottom side and goes pretty much straight up through the roof.

We set up data logging USB thermometers, both inside and outside the building and let them run for a couple days. Here is the graph with inside and outside temperatures over-layed:

And some newer images of the stove, now that it's been plastered.
This is just a base coat. It had too little fiber in the plaster and has cracked along the lines of the bricks. It looks pretty sweet just like this, but at some point it needs a whole new layer of high fiber plaster, then a color coat.

It looks as though there is primary air from the left side, is that correct?
Is there secondary air being added at the throat?

Alley Bate wrote:It looks as though there is primary air from the left side, is that correct?
Is there secondary air being added at the throat?

Both primary and secondary enter in that same opening. There is a metal channel that moves secondary air to the throat at the back and an air slot below the door that feeds primary to the front.

That metal secondary air channel is the only part of the stove that can not be easily replaced with some kind of neo-lithic mud mixture.. I'm working on an idea, but am not there yet.

Hi, Donkey.

I really like that one! But have some questions to understand the build better...

Do you have an approximate figure of effective inner surface area?

The front and back wall of the arch - you just filled it with bricks on side and then stuffed the gaps?

Did you use anything to compensate the outward force at the bottom of the arch? Or is it so steep that it doesn't matter?

Is the heat riser made from clay and perlite mix or is it something else? It looks to me like that you had some form inside but then you removed it...

How long is the firebox from the primary air gap to the last wall? How long firewood can you utilise?

Is there something that you would do differently if one says: "Please, make me something like that!"

What are the dimensions of the bricks that you are using?

Few years ago i did a casted 4" batchbox with p-channel. I had a feeling like that it is kinda too small of a sistem to work well. Maybe i should insulate around the 3cm casted firebox walls... Looking at your graphs it seems that yours is working well!

And i really like this kitchen utensil for the door! These doors  are the cherry on top! It looks like that the stove is saying to other heaters: "Look i can do it better with a casserole than you with a $$$ metal door!"

Thank you for sharing and i hope to hear more details about jamboree projects!


Best regards

klemen urbanija wrote:Hi, Donkey.

I really like that one! But have some questions to understand the build better...

Hey Klemen, long time!

Do you have an approximate figure of effective inner surface area?

Sorry, I forgot the numbers and it changed quite a bit as we worked. One thing I can say is that the ISA of the bell was intended to be undersized. We needed to insure high velocity through the system, so the chimney runs hotter than we would with a larger system.

The front and back wall of the arch - you just filled it with bricks on side and then stuffed the gaps?

Yep. We used bricks, brick bits and filled with cob.

Did you use anything to compensate the outward force at the bottom of the arch? Or is it so steep that it doesn't matter?

We used a catenary arch to reduce thrust. The Bottom course comes just not quite flat, so thrust is minimal. We did put in some stainless steel straps just in case and we watched them carefully as we added arches. They never tightened or moved, hopefully they stay that way.

Is the heat riser made from clay and perlite mix or is it something else? It looks to me like that you had some form inside but then you removed it...

It's perlite/clay. The inner form was the same piece of 4 inch  chney pipe that we used for the chimney. We packed in the mix and slipped up the pipe as we worked.

How long is the firebox from the primary air gap to the last wall? How long firewood can you utilise?

The firebox is 18 inches deep. The longest wood can be around 16 inches. The regulation box length, according to the numbers for a 4 inch batchrocket is just too short to be conveniently useful.

Is there something that you would do differently if one says: "Please, make me something like that!"

I'd make a longer bell. It was too short and didn't leave room for the riser to go in straight and allow flow to the chimney. It forced us to offset the riser to one side, which made the double rams horn pattern impossible. I think we made up for it pretty well with the single sided cyclone, but I wanted to look down and see those horns!!

What are the dimensions of the bricks that you are using?

Standard red brick. I forgot the exact numbers. Man, I'm really terrible at remembering that kind of detail. I believe they were intended to be for a 4.5 by 9 space, including mortar.. wish I could do better than that.

Few years ago i did a casted 4" batchbox with p-channel. I had a feeling like that it is kinda too small of a sistem to work well. Maybe i should insulate around the 3cm casted firebox walls... Looking at your graphs it seems that yours is working well!

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).

And i really like this kitchen utensil for the door! These doors  are the cherry on top! It looks like that the stove is saying to other heaters: "Look i can do it better with a casserole than you with a $$$ metal door!"

Ha! Thanks.. yeah, there was a lot of head scratching about how to go about making a cheap easy door for this. The firebox mix is inended to be able to make anyplace in the world, by the poorest people.

The door and also the metal P-Channel are the stumbling blocks to that. This door solution removes it from the list and I wish I can say it was my idea. Chris McClellan came up with it and kudos to him! Still need to find a reasonable replacement for the metal P-Channel.

Thank you for sharing and i hope to hear more details about jamboree projects!


Best regards

Cheers!!

Gosh, Donkey, that was fast!

Did you start writing reply prior to me writing the question ?!?

Thanks, much appreciated info!

Regards!

Standard building brick usually works on an 8" modular pattern once you add mortar... 3 courses is 8 inches tall, 1 brick is just under 8" long (with mortar, they are 8" apart), and 1 brick is just under 4" wide.
https://i0.wp.com/civilengineerspk.com/wp-content/uploads/2016/12/commercial-masonry-boston-ma.jpg


Our bricks were the 3-hole kind, I'd guess they were 3.5 x 7.5 x 2.5 or so (I'd go with "Standard Modular" from the chart above, but they could have been Standard or Series 70, I suppose).

Because of the small size of the fire, and the chimney, the heat extraction balance is critical.  
This heater performed really well in that respect - once dry, it put enough heat out the chimney to get reliable draft, and the chimney was touchably warm but not excessively hot.

Donkey talked about making it a little longer, to have room to center the heat riser - but if you did that, you'd also have more extraction surface.
I might suggest also raising the firebox if you did lengthen the body, to balance out the surface areas, and to make it more convenient to load and operate.  
Ernie had trouble getting the fire started properly (people commented on the smoke on two different occasions) because he is tall, and unable to get down on his knees due to old injuries.



Rough guess as to internal SA based on the pictures:

Main Heat Extraction Surfaces of Bell:
The firebox moulding fills up the first few courses, up to the height of the 'arms' in front by the door, back to the heat riser.
Above that, it's 9 horizontal courses before the bell, and internal dimension is 3 bricks (omitting the half-brick wall thickness front and back), by 1.5 bricks.
So the inside of that chamber would be about 24" by 24" by 12".  SA = 2(24x24)+2(12x24)=1728 sq. inches.  

The inside of the dome is 6 brick-edges tall on each side, by 24" long, so roughly (16"+16") x 24" = 768 sq. inches
The end caps of the dome look to be maybe a square foot each, rough guess, or 300 sq. inches total.

Total of the inside bell surface areas: 2796 square inches, or 19.4 square feet, or 1.83 square meters.


Lesser Extraction Surfaces:
Not sure whether to count the firebox top; that would be an additional 12x24=288 sq. inches.

The heat riser is in there (8" cylinder, extending from the floor up to the rim below the arch); exposed SA about pi*8*24=602 sq. in.  
Not sure whether it counts for surface area; the mix of that and the firebox looked dense enough to store some heat, but they also function as insulation.

Beside the heat riser, the path going down to the chimney is also about 8" long by 4 or 5" wide by about 12" or 13" tall. If we count it, it's roughly 12" by 24" total, another 288 sq. inches
I think Peter sometimes doesn't count the bottom surfaces due to lower temperatures, so we may be able to omit this too.

If we did count all those surfaces too, then we'd have another 1178 square inches, or 8 square feet, or 0.77 square meters.
Total would then be 2.6 square meters / 27.5 square feet / 3974 sq. in.

Plus a bit for the firebox itself, if we like.  That was 18" deep by about 8" tall by 5" wide, so 380 sq. inches or so.
I believe this is usually not counted - however in this build, I think that block of refractory at the bottom was a significant factor in holding heat through the night.

Another calc we could do might be total mass of the system.
A cubic foot of this dense building brick weighs about 125-150 lbs.  A cubic foot of brick would be about 20 bricks. I'll go with 135 lbs/cu ft for estimating.

13 courses x 13 bricks per course + 6 bands x 8 bricks per band = 10 or 11 cu ft of brick.
+ 1 cu ft arch ends and wedges
+ 2 cu ft firebox and heat riser (I'm counting a 5-gal bucket of mix as 1 cu ft. for estimation purposes)
= total of about 14 cu ft. of masonry in this project.  
Thermal Mass (without footing)= 1850 lbs = 0.9 Imperial tons or 0.8 metric tons / 840 kilograms)

...
Incidentally, for US code purposes, this would definitely qualify as a masonry heater (over 1500 lbs per the US standard description).  
However if someone wanted to build a pre-fab model, it could also squeak in under the definition of a wood burning stove (1980 lbs max).  
If you can pin all that masonry together for shipping, and add a door, and replace the footing brickwork with legs, using not more than 130 lbs of additional steel.
...

Again, the performance of this stove was lovely - the surfaces got very hot, but not dangerous to touch (a little hotter than I'd want my bath water, however the brick and plaster are less conductive so it was not painful to touch).  Heat storage is figured on mass x heat capacity x difference in temperature, so the hotter you can get the mass (within safety limits), the more heat it stores.  
Donkey really nailed this one, I don't think it would be improved with either more mass, or less mass.  It's probably within 2  cu ft of absolutely optimal, and may be optimal as-is.

I will be interested to see how it does with its final coat of high-fiber plaster... I anticipate that will give it slightly more mass, insulate the existing mass for a slightly higher internal temperature without causing the external temps to become uncomfortable, and may slightly extend the heating curve later into the mornings.


-Erica

The heater core (including riser) and floor are not counted in bell calcs. Internal pillars and whatnot are.

Thanks Erica, that's awesome!

I did some calculation when the red cabin heater was built. If I remember correctly this heater was calculated at 2.15 m² ISA while the maximum for such a tiny construction according to the accepted values is 2.35 m² ISA. The core is rather voluminous so there are some surfaces that are bound to extract some heat while not being calculated. In all, there's a fat chance the whole of the heater is quite close to the very edge of what is possible to achieve without running into dirty burns and smoking back...

Note that this is the first time ever of using the "casserole door".  

Vortex on Donkey's forum used casserole door on his cabin stove nearly ten years ago - just saying

A video dedicated to The Cyclone Tiny House Rocket Mass Heater!

Hey, thanks for sharing! Very inspiring...

Glad to hear about someone using their own homemade refractory mix for the firebox. Perhaps you could have used the same mix for the heat riser/internal chimney (with added insulation maybe), or are there any reasons not to?

I have heard about wood ash before, being an interesting choice for making your own refractory mix, but washing out some elements, especially potassium, with water, seems to be important. Unwashed wood ash is actually lowering the melting point of the mix, correct? And washing it with water makes it increasingly more refractory? So did you wash your ash before use?

Does cow dung have some properties that add to the refractory nature of the final mix or is it there as a binder and agent to minimize cracking or something?

I am very interested in learning about the ratio between wood ash, grog, cow dung and clay soil? Did you test different mixes before building? Did you make use of some existing guidelines and tested recipes?

You do not have any extra insulation around your ash-clay-dung-grog firebox, other than the insulation contained in the mix it self in the form of ash?

This batch rocket mass heater sounds like a home-made version of a central European kackel ofen.  Very good.

In many ways, it is. the major difference is the development of the (batch box) rocket combustion core, which makes a cleaner, more efficient burn than most anything else available.

A video about the casserole door:

Love this heater. Maybe I have missed something, though. How do you clean it out? Is there an opening that I do not see?

Tiffaney Dex wrote:Love this heater. Maybe I have missed something, though. How do you clean it out? Is there an opening that I do not see?

Pull out the exhaust duct.

Questions from an absolute (urban-dwelling) newbie. Really, really, REALLY wanting something along the line of this rocket mass heater for my small den, in place of the existing freestanding gas stove. It would need to heat the den, the small kitchen (no wall between the rooms) and the adjoining small office.

Would I need to get a permit from the Powers That Be? Do permits for such even exist? I'm in lovely Fresno, CA

What might happen if I didn't bother to get one?

Blessings!
Ann~

I would like to build a stratification chamber around a Sedore 3000 biomass stove.  Reason: the stove throws a tremendous amount of heat into the room and it gets HOT.  I don't want my dogs and cats and spouse touching the scaling metal.  Also I could not find a builder to build a rocket mass heater and can't build one myself.  So, I shelled out some big money for the Sedore 3000 but would like to improve its user friendliness.

Love the stove, but would like a lingering heat in a bell with a top that could swing open to access the top-loading portion.

Has anyone got any experience building a bell around an existing woodstove?

Thanks!

Really love this design. I have been wanting to put in a RMH at my place but I could never figure out a spot where the bench could go. The one spot I have would fit this type of design fairly well. Thanks for sharing!

Daron, have you se en this one?

http://batchrocket.eu/en/applications#redbell

Satamax Antone wrote:Daron, have you se en this one?

http://batchrocket.eu/en/applications#redbell

Nope - thanks for sharing! I'm in the very early stages of learning about RMHs. Love the concept but struggled with how to fit it in my place. It will be a few years before I'm ready to go down this route but I'm trying to slowly learn the concepts and get a sense of what is possible.

This is the space I have where one of the vertical no bench designs could fit. Another option might be to replace the natural gas insert but that seemed more complex to me. Either way the space would need to be modified but I like the idea of adding an RMH to heat my main living area.

Question about these bench less designs. From watching Paul's recent videos it seems like one of the big advantages of an RMH is the idea of heating the person through the bench/mass instead of relying on heating the air and then the person through the air. But these bench less designs would rely on heating the air. Is that correct? I know the mass would still hold heat and slowly release it which would provide an advantage over traditional heaters. But I'm guessing that bench less designs may need more wood than the designs with the benches to keep people warm since you can't sit on the mass. Is that what people are experiencing with these designs?

Do you have a chimney?  At which floor this is at?

Daron Williams wrote:

Question about these bench less designs. From watching Paul's recent videos it seems like one of the big advantages of an RMH is the idea of heating the person through the bench/mass instead of relying on heating the air and then the person through the air. But these bench less designs would rely on heating the air. Is that correct? I know the mass would still hold heat and slowly release it which would provide an advantage over traditional heaters. But I'm guessing that bench less designs may need more wood than the designs with the benches to keep people warm since you can't sit on the mass. Is that what people are experiencing with these designs?

Hi Daron,  I have a new batch box masonry bell similar to this one, and about the same age, too!  I finished it last month, and now that it has dried out, we're burning it usually twice a day for 1-2 hours at a time (around 2-4 loads of wood).  It puts out heat like a radiator once hot, and that lasts for around 6-8 hours.  It heats up the two downstairs rooms with that radiant heat, and if we are really cold, we can sit up against it on our piano stool to warm up.  

Bear in mind we live in a cool, not cold climate--we don't often go below freezing during the day, and usually not at night either.  I can't say what it'll be like for us for the rest of the winter, but for the past month, using this heater has been comfortable enough for us to go without turning on our central heating.  We hang out downstairs during the day/evening and take hot water bottles to our unheated bedrooms to sleep.

A masonry bell will heat the air, as will all heaters to some degree, but it will mostly give radiant heat which warms people, furniture and walls directly. There will be less of the conductive heating which makes benches so nice, but it is not likely to take significantly more wood.

Natural gas insert is where a fireplace would have been and there us a chimney. Thought about having RMH connected to it though this is not an area I have any experience in.

Thanks for sharing your experience! Sounds like it would work fine in my climate. Zone 8 here and never gets very cold - I grew up in a much colder area so for me the winters seem mild in zone 8. My house is poorly insulated but I hope to fix that one day.

Thanks all for the info. I will keep this design in mind as I keep studying up on RMH.