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rocket mass heaters

Shorty Core gets a bell

thomas rubino

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posted 6 months ago

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Early this summer Gerry and I assembled and tested Peter's newest core design The Shorty Core.
https://permies.com/t/234638/Development-compact-batchrocket-core
Here are my threads all about my build.
https://permies.com/t/254292/Airframe-Construction-Shorty-Core
https://permies.com/t/254283/Shorty-Core-Montana-Version-burn
I believe this is the first one built in the US.
Gerry returned on October 5th, and we started preparing to move Shorty into my 100-year-old cabin.
10 days later Shorty has a new bell and my valley has a new Dragon patrolling the sky.

Removing the old steel stove and the cement and rock pad it sat on was the first job tackled.
Next, we fit 1/2"of cement board over the subfloor.

I would have loved to make this into a double-skin bell, but the size and weight restrictions forced me into building Shorty a single-skin bell.
Shortly after getting started on the first run of bricks, I offered Gerry the trowel and the job of the lead bricklayer... I took the job of hod carrier, and mortar mixer as well as lead custom-cut brick fitter.
Both jobs are important and having competent help makes the job faster, easier, and the final product is much finer than it might have been had I worked alone.

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home built 3/4" thick Alaska pipeline wood stove

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thomas rubino

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posted 6 months ago

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Due to access on the north side, we built up first to avoid leaning over the completed brickwork.
A block out was added for the clean-out door, and steel plates were put down to better distribute Shorty's weight (I'm not saying she is Fat or anything).
An angle iron frame for her to rest on was the start.
Shorty requires three custom-made slabs as a roof on the core, the riser, and a part of the riser port
After assembling the lower portion of the core, the door and angle iron tension frame were set in place and Superwool was inserted on the walls.

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adding a block out for the cleanout door

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High temp heat sensor placed in riser brick

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door set, tension frame and Superwool are going in

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Pablo Kulbaba

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Location: Chascomus, Buenos Aires, Argentina

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posted 6 months ago

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Nice!
Please tell me the name of those red bricks. How do you call the, over there? Here in Argentina they would be "Pressed bricks", or "Machine bricks".
How much do they cost each?

Pablo Kulbaba / Hacono Estufas
www.hacono.com
www.lestufer.com.ar
Argentina

thomas rubino

rocket scientist

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posted 6 months ago

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Hi Pablo;
Those bricks are called new clay bricks at Home Depot.
They cost.58 cents apiece. I used apx 400+ in this build.

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Peter van den Berg

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posted 6 months ago

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Go on, go on, this is very interesting!

The placement of the 8" to 6" reducer looks good to me, using the blinding plate as lintel is a nice move. To my eye, the exhaust opening in the brick bell looks like 1.75 bricks wide and two layers high, is that correct? That would make an opening about 2.5 times the chimney's csa, which is absolutely adequate.

regards, Peter

Gerry Parent

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posted 6 months ago

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Thank you for the encouragement and confirmation that we are on track Peter!
It has been a very enjoyable build.

Silence is Golden
For all your RMH needs:
dragontechrmh.com

thomas rubino

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Yes, the exhaust outlet is apx 12" wide and 4.75" tall, in conjunction with the 8" to 6" reducer is performing superbly.
Shorty's claim to fame is her unique riser
Very short, it starts out as a standard 6" riser. With its extra deep port, it creates a powerful double ram horn.

https://www.youtube.com/shorts/vgqa2YJVsbM

Above the port, the riser increases in size slowing the gasses, and goes up to the heavy cast Roof of the riser... (yes the riser has a roof!)
Hitting the roof causes the gasses to turn down and exit horizontally from the riser port directly over the -core itself.
Completely different from a conventional design Batchbox that blasts its heat toward the roof of the bell

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thomas rubino

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Location: latitude 47 N.W. montana zone 6A

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With her brand new design, Shorty's performance enclosed in a bell is still unexplored territory.
Here at Dragon Tech we are forever pushing boundaries and trying things that have not yet been done.
Gerry's and my work on this build reflects true experimental rocket science into the unknown.

Traditionally, firebricks or insulation are required as a roof over your riser.
In this build the core is completely wrapped with Superwool, keeping the core hot at all times.
Apx. 5" over the top of the riser we have a split firebrick roof supported by 1.5" angle iron T bars, wrapped with 1" of Superwool blanket and sitting on Superwool gasket.
These will be covered by 4x4" tile.
At the front, sitting on the core over the door airframe, we have a triple stack of heavy firebricks protecting the plain bricks.

Just behind the riser, we have built a beautiful arch using regular clay bricks with no firebricks or Superwool insulation at all.
Conventional wisdom would say that this is doomed for failure. Plain clay bricks cannot withstand much more than 800F constantly without deteriorating.
We have placed a digital probe at the top of the arch to closely monitor this location, as well as one in the exhaust pipe.
Early readings while the bell is still shedding moisture are extremely encouraging!
The riser temps are running 1200F, the top of the arch has yet to reach 380F and the exhaust temperatures are 130F.

These numbers will change as the bell continues to dry.

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For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
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thomas rubino

rocket scientist

Posts: 6524

Location: latitude 47 N.W. montana zone 6A

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posted 6 months ago

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Originally my bell was going to have a step deck, lower over the core (like it is) and then a tall square tower behind it.
Luckily, I sat down with a calculator and ran the numbers on my ISA (internal surface area). Had I built what I had in mind, I would have exceeded the maximum size for a 6".
After changing the design I now have apx. 55-56 square feet of ISA, the allowable amount is 57 square feet.
Gerry deserves credit for suggesting the creation of the arch.
As previously mentioned, this arch is constructed with plain clay bricks with no extra insulation.
This was a calculated risk as nobody knew how Shorty would perform inside a bell.
Although she is still wet behind the ears, all indications are that my gamble has paid off, Shorty's design keeps the hottest gases down near the core and not at the top of the arch.

Shorty also has a newly designed bypass on her.
Most bypasses have been constructed using a sliding gate, often called a blast gate.
For Shorty, I went old school and installed a traditional cast iron stove pipe damper (the same kind Grandpa used)
I cut and wired on a piece of Superwool gasket to block the holes that a cast damper comes with and to help keep the heat in the bell.
With the exhaust stack so close to the wall of the bell, we used a 4" 90-degree bend with the damper in the middle.
A 4" hole was carefully marked and cut in the 6" pipe, and the 90 is inserted through the back end wall of the arch at the top.
This will alleviate any hard-starting issues as well as allow Shorty to fly during the shoulder seasons without roasting us out of the house!

I will mention that once Shorty got her core warm, there have been no starting issues.
One piece of paper, some cedar kindling and she literally leaps into the sky to soar around our valley!

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Glenn Littman

rocket scientist

Posts: 178

Location: Sangre de Cristo Mountains, CO - Lat 38°14' - Zone 5b

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posted 6 months ago

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Bravo! Congrats Tom... looks fantastic. <<edit>> and kudos to your flight mechanic Gerry for his skills and contribution. Is he available to visit Colorado to help with my shorty core build?... And thank you for the fine effort to implement Peter's shorty core design.

The shorty core design is intriguing as it simplifies the firebox by eliminating the secondary air intake with the trade-off of a somewhat more complex door/air intake design. Also, the elimination of the tall riser has great benefit with the elimination of lots of insulated fire brick. This presents the builder with bell height design flexibility as a result of a core height that is significantly lower.

It will be very interesting for all to hear your performance reports as winter moves into Montana and shorty has an opportunity to fly.

Rocket surgeon and soil builder... healthy plants are all about the soil.
- My 6" Batch Rocket specs and materials list: https://permies.com/t/248275/Batch-Rocket-Double-Skin-Bell
- Batch Rocket detailed build thread with Q&A: https://permies.com/t/238503/Batch-Rocket-Build

Glenn Littman

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Location: Sangre de Cristo Mountains, CO - Lat 38°14' - Zone 5b

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Tom, are you able to get a picture or two of the back to show the bypass tie-in? I assume that was a tight fit to get in there and make the modification post-build.

thomas rubino

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posted 5 months ago

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Here you go, not very good at all, but access sucks.
We added a 5" straight section on the bell side and removed two bricks from the arch top.
Some custom brick cutting and lots of cob mortar sealed up the bell side.
I did a very snug cut in the 6" pipe, we cut out any excess that stuck inside the 6" pipe so as not to impede the gas flow.
Metal duct tape seals the connections in several spots.

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For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
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Glenn Littman

rocket scientist

Posts: 178

Location: Sangre de Cristo Mountains, CO - Lat 38°14' - Zone 5b

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Nice work for such a tight spot. Love the old school cast iron damper with SW gasket.

thomas rubino

rocket scientist

Posts: 6524

Location: latitude 47 N.W. montana zone 6A

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Shorty Core Performance Update,

Shorty is finally drying out.
The drips are almost gone from the stack pipes..
It has been so warm that even one fire a day caused us to have a window open all night.
Finally, today it is getting cold enough, so I had a morning fire, as well as a studio fire and a shop fire!
This afternoon while sitting next to Shorty I still felt chilled so I lit her off again... Man, this is SO NICE with the gentle heat rather than the scorching heat the old stove gave off if you opened it up.
My riser so far seems to like the 1200F range
The arch top has not gotten over 380F
The exhaust stack just this afternoon started rising from 130F and hit 180F and has now settled around 167F

There was some concern that my arch top would get too hot and I would need to open it up and add Superwool.
Shorty's horizontal exit is holding the heat mid-bell rather than blasting it up to the roof of the bell,
So far the clay brick surface temps near the core are 150F or less, and the arch top is running 110F.

With no secondary air tube in front of her riser port, care must be taken to leave a gap between the wood and the port opening while loading wood.
This is no problem as you only need one load at a time, currently, other than yesterday I'm going 24hrs between loads

She flies so different from the other girls, soft, steady, calm, but still pumping out the heat.
The others roar and fly about and then want a nap... Shorty's just cruising!

The bottom line, in my opinion, the Shorty Core is harder to build having to hand-cast large slabs.
But her short stature and increasing performance have put a large smile on my face.

I highly recommend considering a Shorty build, she will not disappoint you!

A tip of my hat to Master Builder Peter Berg he has done it again and developed what I believe is equal to or even better than his original design Batchbox!

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Scott Weinberg

Posts: 317

Location: North East Iowa, USA

posted 5 months ago

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thomas rubino wrote:Shorty Core Performance Update,

Shorty is finally drying out.
The drips are almost gone from the stack pipes..

Tom

All sounds excellent on your Shorty build, Just the two questions, by drying out, do you mean the mortar used for your exterior brick work?

And what is meant by "stack pipes"

thanks.

https://permies.com/t/241976/Batch-Rocket-single-bell-build

thomas rubino

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Yes, the mortar and bricks hold a large amount of water that must evaporate and leave before Shorty can be her best.
The "stack" pipe is simply the exhaust pipe leaving the bell and rising through the roof.
The movable 90s hold moisture and fill up, creating drips that run down the pipe.
These are now drying up and with the rise from 130F to 167F they will not be returning.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
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Joy Art

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Hi Thomas,

I am not sure how to make an image attachment, but those two images that you posted that are dark, I lighten them up for you, to better see the details.

That is a amazing! All of your work.

Would you by chance have a map / layout / or drawing of how you layered the inside firebricks?

Thank you!

thomas rubino

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Yes, Peter graciously supplied me with a build sheet for Shorty.
It is straightforward and could easily be duplicated by looking at my photos.
The air supply frame is the most technical portion of the build.
The door itself is very simple.

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Joy Art

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Hi Thomas,

That was very kind of Peter to do that.

What is the final foot print for shorty?

Please forgive my ignorance with this question, but is there any creosote?

thomas rubino

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Hi Joy;
Shorty's bell is 3' x 4' x 65" tall at the arch.

The short answer is no, there is never any creosote in an RMH.

The longer answer is everything including creosote is incinerated in the riser.

The only thing inside Shorty's bell is fly ash ( a very light ash)

While Shorty is/was drying there was quite a bit of moisture that needed to evaporate, it found any spot in the chimney pipe to seep out.
That seep is black and it resembles creosote but it is not.
Trying to burn wet wood can have the same effect.

The bottom line is you will not need your chimney brushed ever again.

If your skeptical relative happens to be in Montana or Idaho we can show them a dozen fully functional RMhs... None will have any creosote.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
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William Bronson

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Great build!
I am a little confused, is the arch sitting on top of a firebrick roof?
It looks like you built a roof on top of the inverted t-bars and built your arch on top of that, but that wouldn't leave a way for the gasses to get to your by-pass, so I'm missing something.

Eating Bindweed
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thomas rubino

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Location: latitude 47 N.W. montana zone 6A

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Thank You, William!
The arch bricks are supported by a full double tee bar to safely hold the weight.
The lower roof (split firebrick) starts out sitting on a single angle butted up to the arch and double T- bars for the rest.
All the T-bars are wrapped with 1" of superwool

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
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thomas rubino

rocket scientist

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Location: latitude 47 N.W. montana zone 6A

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Check it out!
The tile I ordered arrived today.
I just had to dry-stack it!

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For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
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Glenn Littman

rocket scientist

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Location: Sangre de Cristo Mountains, CO - Lat 38°14' - Zone 5b

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Love the tile touch, looks great!

You mentioned earlier in the thread that the external brick closest to the core is running around 150 deg. What kind of temps are you seeing in that location in the mornings before you fire her up again?

thomas rubino

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It has been a solid 85F top to bottom 24 hrs later.
The side bricks when running are 180F-190F now that the moisture is gone.

We are still looking for the perfect metal art to hang on her, just like that good-looking one in Colorado.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
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Glenn Littman

rocket scientist

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thomas rubino wrote:We are still looking for the perfect metal art to hang on her, just like that good-looking one in Colorado.

Yup... gotta add a little heater bling :-).

Matt Todd

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This build is really making me question the conventional wisdom that says everything above the heat riser needs to be double skinned with a refractory (usually firebrick) inner layer.

I went on a deep dive to see what temperature red clay brick is fired at and across 9 sources 800C (1472F) was the minimum and 1200C (2192F) was the maximum.

There are not many sources for temperature readings inside a brick bell, but one well documented case on the Donkey32 board measured 600C (1112F) at the bell ceiling with temps dropping quickly down the bell wall.

While I would still use firebrick in the ceiling (out of an abundance of caution) I'm really seeing no reason to continue firebrick down the inner walls. Aside from the fact that firebrick comes in splits which helps save space to make a double skin.

I see you put a thermocouple in the riser. Did you happen to put one anywhere in the bell?

I don't own the plants, they own me.

thomas rubino

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Yes, I have one at the top of the arch and another in the chimney pipe shortly after exiting the bell.

Shorty Core is a whole new design.
There are very few built and installed in a bell at this time.
We are all learning about our newest Dragon Shorty, and how she reacts to her new environment.
Unlike traditional design Batchboxes her highest heat seems to stay mid-bell, while the others blast their highest heat directly at the roof.

My version of Shorty utilizes a split firebrick roof apx 5" above the riser level.
Shorty's horizontal exiting riser sends her heat casually up and toward the front wall of the bell.
I dry stacked, 6 full size firebricks on top of her core directly in front of the riser exit to protect the clay brick bell above the airframe.
These are the only firebricks I used in the bell. My arch is solid clay bricks.

A word on solid clay bricks. Indeed they are manufactured at high temperatures, however, they cannot maintain integrity at those levels.
I consider 800F a maximum safe operating level that your bricks can be expected to maintain without degrading. (the true number I'm sure is higher)

With Shorty being a new design and my bell (arch) being unconventional, Peter and I were concerned about how hot the arch top temperatures might go.
I installed the temp probe to know exactly how hot it would get and I was prepared to open the arch and install superwool if needed (I sure hoped it was not!)

I am very happy to report the highest temps my arch has risen to are just over 400F!!! (Success!)

I am still in my first month of getting to know Shorty, sort of like having a new girlfriend.
Real winter is not here yet, I need an entire winter's worth of living with her, to know how fiery hot she might get, after all, she is a dragon...

Here is a video of Shorty's casual burn on a single half log tossed on a glowing bed of coals.

https://youtube.com/shorts/kSoJPfTQS-M?feature=share

In a traditional Batchbox, this log would be roaring into the riser port, Shorty is just cruising along with it!

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
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G Mack

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Nice build Thomas...and thanks for sharing your knowledge on rmh design. Is the cast slab over burn chamber also gasket fit or mortared to top wythe of fire brick ?

thomas rubino

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Good eye G;
We used mortar on the slabs.
We were low on gasket by then.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
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G Mack

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Ok... practical not technical. Just asking because I was thinking that may be a joint of differential expansion due to cast slab / fire brick differences as well as orientation ( wall / ceiling) and thought gasket fit was perfect there. Did you cast slabs at thickness similar to bricks for expansion reasons? I seem to recall Peter mentioning castings should be on thinner side for quicker temp response. Always weighing strength, function and economy... I am considering 1.5" thick casting spanning 9". Any comments on that thickness?

thomas rubino

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They make commercial cast slabs from 1.5" up to 3" so it works.

I made these slabs to the thickness that Peter suggested.
We heated them slowly to confirm any moisture evaporated before subjecting them to Batchbox temperatures.

I am always concerned with how solid the casting turned out with any home casting.
If I poured a slab at 1.5", I would be very concerned about it cracking and possibly failing mid-winter.
At the least, I would pour a second, spare slab to have on hand in the event of a mid-season repair.

If you have access to a professional vibrating table, your results would be much more trustworthy.
When working with a homemade vibrating table, results can vary,

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com Once you go brick you will never go back!

G Mack

Posts: 6

posted 5 months ago

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No casting experience here. Thanks much for your input.

thomas rubino

rocket scientist

Posts: 6524

Location: latitude 47 N.W. montana zone 6A

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posted 5 months ago

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Hey G;
This was my learning curve.
https://permies.com/t/254174/Casting-Large-refractory-Slabs

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com Once you go brick you will never go back!

Scott Weinberg

Posts: 317

Location: North East Iowa, USA

posted 5 months ago

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G Mack wrote: Always weighing strength, function and economy... I am considering 1.5" thick casting spanning 9". Any comments on that thickness?

by spanning 9" do you mean your casting will be longer than 9"? or a casting that is 9" in length?

If the latter, it would be hard to be more economical than a fire brick, whole or split to span, but you would need less than 9" for this to span. Thus my question above.

Or, just for consideration--

I spanned 11 3/4" with simple brick arch truss, and have never looked back, and if you use a tension frame, it is easy peasy to keep the brick truss from sliding flat or falling in.
works with or without mortar, depending on use of super wool of 1/8" placement.

Filename: close-up-of-brick-truss.PDF

File size: 483 Kbytes

Download Attachment

https://permies.com/t/241976/Batch-Rocket-single-bell-build

Scott Weinberg

Posts: 317

Location: North East Iowa, USA

posted 5 months ago

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for those that don't want to down load a pdf here is a jpeg of the same view

close-up-of-brick-truss-or-arch.JPG

Green bricks are fire brick with simple angle arch. Does require cutting.

https://permies.com/t/241976/Batch-Rocket-single-bell-build

G Mack

Posts: 6

posted 4 months ago

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Hi Scott. Yes saw your build post and am heading in that direction. Bought roof fire bricks yesterday. Thanks for your comments and build sequence.

Scott Weinberg

Posts: 317

Location: North East Iowa, USA

posted 4 months ago

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G Mack wrote:Hi Scott. Yes saw your build post and am heading in that direction. Bought roof fire bricks yesterday. Thanks for your comments and build sequence.

Your welcome concerning the post. As you have noticed I do a lot of CAD work in my profession, so thought I could show the different layouts in color and have them show up better than photos of the real thing. But, I almost always build exactly to how it is drawn. I have built 4 different RMH's, with my last 7" version, absolutely working the best, and I attribute this to the fact, that I built it as close to recommended dimensions. The others were not bad, just that this is so much better.

But I must point out that any of my bridge type roofs, require very good patterns, and a wet tile saw , as there is a fair bit of cutting, but in the end very little waste. But you can't have sloppy joints if your doing a dry stack method, which I tend to do.

And of course with any single layer bridge type roof, you need a "outside of the bridge" tension frame to keep the bricks from sliding away from the center of the bridge. some say it is not worth the time for the tension frame, but I feel the frame is there anyway, (if your dry stacking) so nothing to loose, everything to gain. I would not trust a mortar joint to be the only side slip hold for the top bridge rather be held in place with the tension frame on the outside. I hope that makes sense.

I do have one question, what do you mean by "roof fire bricks" ? Meaning IFB or something different in larger dimensions? Just curious.

Best of success.

https://permies.com/t/241976/Batch-Rocket-single-bell-build

David Wieland

Posts: 251

Location: Manotick (Ottawa), Ontario

posted 3 months ago

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thomas rubino wrote:...
The air supply frame is the most technical portion of the build.
...

I'm still finishing my Shorty that's for heating my greenhouse, primarily the bench. My build uses far less masonry, both for cost and because I don't need or want much space heating, but I can definitely confirm that the air supply frame is the most technical and challenging part for someone who does very little metal work. That said, I expect that it will go a long way to avoiding smoke leak when starting the stove, an issue that has really annoyed my wife with my previous RMH designs. And I know that the greenhouse plants won't care if my novice welding isn't pretty.

John C Daley

pollinator

Posts: 5500

Location: Bendigo , Australia

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posted 1 month ago

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Scott, looking at your image presented I have some questions;
- aqua parts are tension roods?
- brown sections are angle iron farme?
- green bricks are held in place by friction created by the aqua rods?
Thanks

John Daley Bendigo, Australia The Enemy of progress is the hope of a perfect plan
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