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rocket mass heaters

Rebuilding and remodeling the Shop Dragon

thomas rubino

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

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posted 3 months ago

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The 7" Batchbox in my shop has been through many changes.
Years ago, it started as an 8" J-Tube with a barrel and a brick bell.
I was informed by the armchair experts of the time that I could not do such a thing!
I did not listen, built it my way, and proved the "experts" mistaken... (WRONG) With superwool and cob mortar, you can do almost anything!
A few years later, I converted it to my first Batchbox. This was when I learned about batchbox doors...
Initially, I followed Matt Walker's thoughts on using aluminum and Ceramic fireboard (CFB).
After a few weeks, it was a stunning failure, during which time I watched aluminum melt and learned just how powerful and hot-burning Peter's Batchboxes really were!

This was the moment when the first Dragon Technology Batchbox door was envisioned and built.
I wanted a spark-proof door with a window, but nobody made one, so I designed and built the first one.
My second door is proudly installed on Matt Walker's tiny cook stove in his home.
Now, years later, they are installed all over North America!

This stove had an experimental cast-iron roof. I wanted to know if cast-iron could withstand extreme burning.
The answer is... No, it can not stand up to back-to-back fires all day.
It is a viable roof option for a casual-use batchbox. I know of one installed on an 8" for many years with no issues.
This roof needed to go away. I was pleased it lasted through most of the past season.

The other change I made was to turn the entire core 90 degrees, to make loading more convenient.
This required building a new plinth to support the core's new configuration.

Here are the before and after pictures.
Teardown and build posts to follow.

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thomas rubino

master rocket scientist

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

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posted 3 months ago

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Amazing how fast and easy (although very messy) it is to tear down a clay mortar-built stove!
In 2 hours, I had the whole core disassembled and on the floor.
Rebuilding takes a wee bit more time...
When using a clay mortar, you must carefully go up a few layers before stopping and letting the mortar dry.
Unlike concrete, which dries by chemical reaction, a clay/sand mortar should air dry overnight before adding more weight.

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Quick change secondary with RA253ma stub

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

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Posts: 6730

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

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posted 3 months ago

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First, I filled in the west-facing plinth, and then constructed the new south-facing plinth for the core to sit on.
Unfortunately, I should have built the new plinth one brick wider, as I needed to fabricate a metal support piece to hold the front surround bricks safely.
Broken brick, cement-covered old bricks, and sand were all used as fill inside the plinth.

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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!

thomas rubino

master rocket scientist

Posts: 6730

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

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posted 3 months ago

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The base of the core must be firm and level. Constant checking to keep everything square and level.
I needed to fabricate the metal piece to support the front two surround bricks, if only I had made that plinth one brick wider,,,
The firebricks are 2.5" thick, and the secondary tube for a 7" is 2" thick. I used fine sand to bring it up to level with the floor.
Ash will cover and insulate the secondary tube from the high heat.
Once your base is level and your secondary tube is set, you can start stacking walls.

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

John C Daley

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Posts: 5669

Location: Bendigo , Australia

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posted 3 months ago

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Thomas, how many RMH do you have?
This was a dragon rebuild you did 2 yeras ago https://permies.com/t/190599/Finishing-touches-Shop-Dragon-rebuild
Nowt here is the current rebuild and then there is the Shorty Core!!

John Daley Bendigo, Australia The Enemy of progress is the hope of a perfect plan
Benefits of rainfall collection https://permies.com/t/88043/benefits-rainfall-collection
GOOD DEBT/ BAD DEBT https://permies.com/t/179218/mortgages-good-debt-bad-debt

thomas rubino

master rocket scientist

Posts: 6730

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

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posted 3 months ago

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Hi John;
I currently have four.
Shorty Core
The Shop Dragon (two years ago she got the cast iron roof installed as an experiment.)
The Studio Dragon (She is getting a complete tear-down and rebuild next month)
The Walker Black & White oven

I'll have to build a bunk house for the kids, and then I'll give it a Dragon as well!

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!

thomas rubino

master rocket scientist

Posts: 6730

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

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posted 3 months ago

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For a roof, I used a 12" x 12" slab that we had left over from the Shorty core build and four Scamal IFB bricks.
The Scamals are only rated to 1700°F. I coated them with the 5000°F IFC ceramic, and they sit on angle iron Tee-bars wrapped with Superwool.
The metal support bracket was used for the first brick on the surround. This would not have been needed if I had made the plinth one brick wider.
It works, so everything is good for me.

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Setting the roof slab & IFB bricks, superwool insulation in place

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filling in with superwool and cob mortar

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!

thomas rubino

master rocket scientist

Posts: 6730

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

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posted 3 months ago

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I slowly brought up the east retaining wall, carefully tying the two walls together.
I used a long sawsall blade held with vice grips to saw out the old clay mortar and remove bricks where needed.
Next, was lifting the lower barrel over the riser and placing it on the core.
Clay mortar was used to seal the barrel to the core.
Then I used superwool to seal the barrel to the brick wall in the back.
On the front side, I carefully cut each brick close to but not touching the barrel and sealed them with clay mortar.
The bell roof is made of cement board and sits on angle iron tee bars.
It is carefully cut around the barrel, and superwool is stuffed in the crack.

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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!

thomas rubino

master rocket scientist

Posts: 6730

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

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posted 3 months ago

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After the lower barrel was in place and the mortar set up overnight, I was able to install the second barrel on top.
Several years ago, I installed a rope block and tackle over my barrels.
This allowed me to lift the upper barrel and leave it hanging while rebuilding.
Much easier than trying to place it by hand alone.

The first firing after her rebuild went flawlessly.
The only smoke leaks were where the two barrels joined together. They stopped as soon as the exhaust reached running temperatures.
I'll need to remove the clamp and stuff superwool inside to seal it up.
We are still getting morning temperatures in the 30s, so I am happy to have my Shop Dragon back. It makes the shop much more pleasant.

The tiles on top are temporary, I need to choose and order matching ones.
As I learned with Shorty, a careful application of cooking oil brings out the deep, rich, brick red after drying.

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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!

Rico Loma

pollinator

Posts: 227

posted 3 months ago

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Thanks for the many photos to illustrate your process. You are a master of the craft, saving energy one brick at a time

Jeff Pollari

Posts: 37

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posted 2 months ago

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Hello Thomas and thanks for this awesome update. I'm a little vague on why you used 1/2" thread to close in the firebox instead of simply surrounding them with bricks alone. I have leftover CFB I may consider using here since it would be tightly packed away in my stove and not likely to deteriorate packed between the firebricks and the redbrick. Alternatively, I have leftover insulating firebricks as well that probably could fit inside the channel between the inner firebricks and the outer clay bricks.
Did you use durock for the roof of the secondary bell as well?

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thomas rubino

master rocket scientist

Posts: 6730

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

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posted 2 months ago

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Hey, Jeff;
The 1/2" all-thread is to keep the core bricks snug; this is a no-mortar core.
It also firmly attaches the door backing plate to the masonry.
The 1" of superwool is for insulation to keep the core nice and hot.

Yes, the lower brick bell has angle iron T-bars that support a cement board roof.

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: 338

Location: North East Iowa, USA

posted 2 months ago

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Jeff Pollari wrote:Hello Thomas and thanks for this awesome update.
Did you use durock for the roof of the secondary bell as well?

Hello Jeff, I could stand to be corrected, but I have never used, nor have seen anyone else use Durock for any part of the stove. I went back, and again, I could stand to be corrected, but did not see it mentioned.

Please let me know if this is not true

Scott

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

thomas rubino

master rocket scientist

Posts: 6730

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

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posted 2 months ago

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Hi Scott,
My bell top is Durock with no extra insulation..
With the double barrels, the temps are low enough to handle it.

My Walker Black and White also has a Durock roof, but it has 1" of superwool suspended below it.

Durock is also used as a floor plate for building on wooden floors.

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: 338

Location: North East Iowa, USA

posted 2 months ago

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thomas rubino wrote:Hi Scott,
My bell top is Durock with no extra insulation..
With the double barrels, the temps are low enough to handle it.

My Walker Black and White also has a Durock roof, but it has 1" of superwool suspended below it.

Durock is also used as a floor plate for building on wooden floors.

i am guessing this is different terminology, as durock that I am used to, is used under floor tile. or possible shower stalls, if of the correct type. (water=proff)

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

thomas rubino

master rocket scientist

Posts: 6730

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

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posted 2 months ago

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Same stuff your thinking of.

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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!

Fox James

Rocket Scientist

Posts: 815

Location: Guernsey a small island near France.

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posted 2 months ago

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I have used cement board in virtually every stove I have built, where I live standard cement board is called Magply but we get a few different ones.
Some use polypropylene fibres and some use fiberglass fibres, polypropylene melts at 160c fibreglass around 350c - 400c.
The one I use most nowadays is the HTFB made with fire cement and some sort of high temp fibres, that is good for 1000c
I have shown it in many of my videos, i just love the stuff but of course the disadvantage is the cost, HTFB cost around £360 a sheet 8’x4’

Scott Weinberg

Posts: 338

Location: North East Iowa, USA

posted 2 months ago

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Fox James wrote:I have used cement board in virtually every stove I have built, where I live standard cement board is called Magply but we get a few different ones.
Some use polypropylene fibres and some use fiberglass fibres, polypropylene melts at 160c fibreglass around 350c - 400c.
The one I use most nowadays is the HTFB made with fire cement and some sort of high temp fibres, that is good for 1000c
I have shown it in many of my videos, i just love the stuff but of course the disadvantage is the cost, HTFB cost around £360 a sheet 8’x4’

I can see now that there was different grades of this product, that I was not aware of, as my thoughts were zeroed on the very lowest temp. melting poly fibers and was not aware there was some really neat up grades of material. So yes indeed, I have learned something new. Always a good thing.

Scott

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

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