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rocket mass heaters

will this j work?

Posts: 79

Location: North italy

posted 1 month ago

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Hi scientists!
A friend of mine asked me to help him build a rocket at his house. What do you think of the project?
Heating 60 square meters of insulation in a not-too-cold winter.
I don't have much money available, so I was thinking of a J with half-barrel benches covered with raw earth.

I had a few questions:
1) Is the area of a 20cm J 7.1 square meters?
2) Since the wall is plasterboard with hemp insulation behind it, I was thinking of channels that pass under the bench and continue on the wall. What do you think?
I'm attaching some sketches.

3) The benches will extend 1.5 meters on each side. Will they heat up enough?

4) To insulate the J, I thought I only have expanded clay available. I'll use a net to contain it. What do you think?

Thank for your attention and help

IMG20251024194828.jpg

IMG20251024194913.jpg

Cedric

Rico Loma

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Posts: 381

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Some of your success might be in the details, for example the raw earth used. Sand and rock, clay with rock, what do you have at the location?, and will it work as mass or insulation ? It seems you already have a formidable plan afoot!
good luck on your build

Benjamin Dinkel

Rocket Scientist

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Hi Cedric,
I’m sure the fellow scientists will find answers to all of your questions.

As to your 1) I don’t really understand what you mean. You’re building a 20x20cm J-tube? (8 inch) And you want to know the bell surface equivalent?

I also don’t really understand the channel idea. What material will you make them out of?
You say you have expanded clay. Could you use 10cm of that against the wall to insulate the bell from the wall?

To your 3: I think that should work. It all depends on how you make sure that the hot gas can easily distribute to both sides from the manifold. The exhaust will be in the middle reaching down (juice straw style)?

4) I’m assuming you’ll use firebrick to build the whole J? I don’t think that the expanded clay is insulation enough for the riser and burn tunnel. Rockwool (mineral insulation) will work and is pretty cheap.

Hope this helps and that a lot of others will join the discussion.

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Cedric Noussan

Posts: 79

Location: North italy

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Rico Loma wrote:Some of your success might be in the details, for example the raw earth used. Sand and rock, clay with rock, what do you have at the location?, and will it work as mass or insulation ? It seems you already have a formidable plan afoot!
good luck on your build

Yes, I have plenty of clay and sand to use for mass on the barrels.
As they say: may the wolf die:-)

Cedric

Cedric Noussan

Posts: 79

Location: North italy

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Benjamin Dinkel wrote:Hi Cedric,
I’m sure the fellow scientists will find answers to all of your questions.

As to your 1) I don’t really understand what you mean. You’re building a 20x20cm J-tube? (8 inch) And you want to know the bell surface equivalent?

I also don’t really understand the channel idea. What material will you make them out of?
You say you have expanded clay. Could you use 10cm of that against the wall to insulate the bell from the wall?

To your 3: I think that should work. It all depends on how you make sure that the hot gas can easily distribute to both sides from the manifold. The exhaust will be in the middle reaching down (juice straw style)?

4) I’m assuming you’ll use firebrick to build the whole J? I don’t think that the expanded clay is insulation enough for the riser and burn tunnel. Rockwool (mineral insulation) will work and is pretty cheap.

Hope this helps and that a lot of others will join the discussion.

Thanks, Benjamin, I really appreciate your response!

1) Yes, I'm planning on building an 8-inch system. What's the maximum recommended ISA value?

2) I also have some sheets of cellular concrete, I think I'll use those.

3) Yes, exactly.

4) I wasn't aware of this option. Does the rock wool come in a roll? Is it wrapped around the riser like superwool?

Also, it would be advisable to install a bypass, right?

Cedric

thomas rubino

master rocket scientist

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

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Hi Cedric,
To my Knowledge there are no official ISA numbers for a J-Tube.
The only numbers we were given were a six inch J could push 30' of horizontal pipe and an eight inch could push 50'.
When Matt built the first half barrel system he told me it could push five half barrels.
I do not know if he used a 6" or an 8" J-Tube to accomplish that.

Always plan to install a bypass, even if it turns out you do not need it.

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!

Benjamin Dinkel

Rocket Scientist

Posts: 848

Location: Province of Granada, Andalucía, Spain

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Cedric Noussan wrote:
4) I wasn't aware of this option. Does the rock wool come in a roll? Is it wrapped around the riser like superwool?

No, don’t use rockwool instead of Superwool. So don’t make a 5 minute riser, it probably won’t survive the temperature on its own.
If you use firebrick you can just put rockwool around the whole core and then cob over it.

You can see it in my build (of a rocket oven) here.

https://permies.com/t/280509/rocket-ovens/Cob-brick-oven-rocket-technology

It’s the green stuff. I used sheets. But roll works as well.

Proudly presenting RocketMassHeaters.com
A good starting point to all RMH research
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thomas rubino

master rocket scientist

Posts: 6905

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

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Cedric,
The jump from building J-Tubes to Batchboxes happened pretty fast
I now remember that for a while, we were suggesting builders to use 6" Batchbox isa numbers with an 8" J-Tube.
If you do, then be sure to install a bypass.

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: 4705

Location: Upstate NY, zone 5

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My 8" J-tube in a bell (built in 2015-16) happened to use similar ISA as the 6" batch box recommendations and works excellently without wasting extra heat up the chimney.

Glenn Herbert

Rocket Scientist

Posts: 4705

Location: Upstate NY, zone 5

659

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I also found that with my building situation giving good positive draft all the time, a 6" stovepipe chimney works well. Paul also tried a 6" chimney in one of his 8" pebble J heaters and liked it, as I recall. A 4" chimney did not work.

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