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rocket mass heaters

Replacing 55 barrel

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posted 7 years ago

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I’m a bricklayer so want to use as much masonry in my heater build as I can
In stead of a 55 gallon barrel has any one used a block and brick box around the heat riser with a 1/4 or 1/2 inch plate of steal cap above the riser
Then I can channel the hot gasses from there to a masonry mass and or just use it as my mass to store heat

thomas rubino

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posted 7 years ago

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Hi Mark; Welcome to Permies!
The entire build can be masonry and you can have a steel hot plate... Just not over the riser.
A fire brick lid over the riser works well, or a ceramic fiber board with standard clay brick on top, work's even better.
Not even 1/2" plate will resist warping and spalling directly over a riser. Temps of 1500-1800F or slightly higher eat uninsulated steel for breakfast.

Do you know which type RMH you want to build ? A standard J tube or a Batch Box RMH?
Are you familiar with ceramic fiber boards and blankets? They are the cutting edge of RMH building materials.

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

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posted 7 years ago

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Hey Thomas, what keeps a barrel from spalling/warping?
Is it the thinness of the metal?
The cylindrical sides?
Maybe he could use a drastically cut down barrel for the metal top to his masonry "barrel".

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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 7 years ago

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Good question William; I think your right about the thin metal flexing. Plate steel warps.

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!

Mark Marshall

Posts: 4

posted 7 years ago

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Thanks for reply

My first thought was a fire brick cap but thought the steel plate would help give a faster radiant heat then the masonry mass would take over after heat up and after fire is out
But if I can just cap it with fire brick and still have fairly fast heat I’m good with that
This is going in a basement right in front of a existing fire place in a man cave I’m going tie this right in to the brick face of the fire place and hook in to existing chimney
Leaning towards j tube but just really haven’t seen much info on the batch style
I’m not familiar with the insulation board
Thanks for replying any info and ideas is greatly appreciated

thomas rubino

master rocket scientist

Posts: 7070

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

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posted 7 years ago

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You might enjoy reading about my shop build. A partially exposed barrel for quick heat and a masonry bell for long heat. I use ceramic boards and a five minute riser.

https://permies.com/t/94980/Brick-Bell-Shop-Heater. Try not to laugh at my brick work or my constructive use of ceramic products to make up for a lack of skill.

Here is a link to another site. Many serious builders post there as well. There you will find much detailed information on Batch box RMH http://donkey32.proboards.com/

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!

Mark Marshall

Posts: 4

posted 7 years ago

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Thanks for the links
Think I’m going to cap with the fiber board and put a layer of fire brick over that how big of a bell can I go with if I do a 8 inch system

julian Gerona

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Location: Philippines

posted 7 years ago

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William Bronson wrote:Hey Thomas, what keeps a barrel from spalling/warping?
Is it the thinness of the metal?
The cylindrical sides?
Maybe he could use a drastically cut down barrel for the metal top to his masonry "barrel".

The barrel shape prevents the barrel from warping any plate that touches the flame will spall. In most of the RMH flame does not touch the barrel. 1/2 inch thick metal plate with the diameter of a barrel might not warp. but then it depends on the intensity of fire. Brick cap might work but you will need a higher stack. My reasoning here https://permies.com/t/40/105520/RMH-smoking-small

thomas rubino

master rocket scientist

Posts: 7070

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

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posted 7 years ago

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Hi Mark;
When building a J tube RMH there are no hard ISA (internal surface area) numbers.
For an 8" batch box Peter recommends 95.3 sq ft of ISA. Depending on your chimney that number could go higher.

My 8" J tube has a bell that is apx. internal size of 3'W x 5' L x 4.5' T . I have a 14' internal chimney and that helps tremendously. I built 2 solid brick towers inside that bell for added mass. My best overestimate is, I have 80-85' of ISA . In my opinion I can enlarge my bell even more this summer.

I should mention ISA is the 4 walls and the roof (Not if it is C.F. board) the floor is not counted. The bick collums added to mine do count as mass and surface area.

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!

Mark Marshall

Posts: 4

posted 7 years ago

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If I was to go with a batch box how big of a box how big of a opening between the riser and the box I and any ideas on a door

thomas rubino

master rocket scientist

Posts: 7070

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

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posted 7 years ago

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Hey Mark;
Did you mean the distance from the top of the riser to the roof of bell ? Mine is 11" or so on the brick bell shop heater.
My 8" J tube, a conventional mass with pipes has a 2.5" top gap at the riser.

The door is a personal preference for most batch builders. Very common is to simply place a sheet of cf board over the front and brace it shut. Others utilize a standard steel wood stove door with CF blanket insulating it. Kirk Mobert (Donkey) used a glass casserole lid as a door.

Detailed batch box specification's can be found at Donkey pro board ( http://donkey32.proboards.com/)

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!

Glenn Herbert

Rocket Scientist

Posts: 4767

Location: Upstate NY, zone 5

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posted 7 years ago

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Donkey's forum is great for in-depth discussions of systems; for a distillation of the best recommended practices and dimensions, go to batchrocket.eu.

John Harrison

pollinator

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posted 7 years ago

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Mark - for my BB rocket brick bell I used a cast iron oven door as an inspection door on the front. The added benefit is that it starts to radiate heat almost as soon as the fire is lit.

I also incorporated an old Georgian cast iron oven (with door) into the bell structure which also radiates heat quickly as well.

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