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RMH build with Sand as mass - and brick instead of pipe

 
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Hello all
Dont have much in the way of Clay soil round these parts. I saw a docu recently about Sand batteries in finland developed to store heat. Is it possible to use Sand as the thermal mass in the bench?

Is anyone doing so with sucsess?

Also i wanted to ask if its ok to use standard bricks for the flue all the way from the manifold to the exit?

Ive plenty of used brick and thought to build three small walls inside the bench as heat channels.. Are there issues with this?

Many thanks
 
pollinator
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The RMH wizards will be along shortly.

I find that sand acts more like an insulator against heat rather than a thermal mass that readily captures and holds it. I use it for heat shields. Strange but true.
 
gardener
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I think the bricks would work.
I wouldn't want to count in sand to prevent exhaust from leaking into the living space.
 
rocket scientist
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Hi Robert;
Douglas is correct. Sand makes a better insulator than it does a mass.
Think about a hot sandy beach in the summer... you can hardly walk on it without sandals.
But dig down just a few inches and suddenly the sand is nice and cool... A great insulator!
Sand is best used when mixed with fireclay to make clay mortar.

Using regular clay bricks for anything but the core itself is fine.
For the core, firebrick is your best option.
In fact, I encourage people to build a brick surround for their mass containment.
It looks good, it holds heat, and best of all you will need very little clay in your mass.

You can create a "bell" when using bricks. A bell is nothing but an empty brick box that heats up, the exhaust outlet is located near floor level allowing only the coolest gasses to leave.  Hot gas is constantly being added from your firebox pushing the cooler air down towards the outlet. That design is also called a stratification chamber.
Stacks of brick or large rocks are common inside bells, anything that is heavy and dense to hold heat longer.
Bells can be any shape that fits the room, a tall skinny box or a bigger square box, or a bench you can sit /sleep on.

If you prefer a piped mass and a solid mass bench then the same brick containment is used.  8" stove pipes  OR  8" square brick tunnels are at floor level with several inches of insulating material under them.  Large heavy rocks are placed around the pipes.  
You say you have very little clay in your area, that's ok. I'm sure you do have mud, wet dirt/clay/debris its all usable in place of clay.
All you are doing is filling all the air spaces around the pipes and then you slowly fill up your mass. adding as many large rocks as you can and filling in between with mud.  When you reach wall height you can brick across the top or you can use cement pavers as a top, large flat rocks look very good as well.

What style of RMH were you thinking of?
Tell us more about your house and where you want your RMH to be.
Do you have an existing chimney?
So many questions and so many choices.
Give us some info and we will help guide you to a successful RMH build.  


 
Robert Grantham
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thomas rubino wrote:

What style of RMH were you thinking of?
Tell us more about your house and where you want your RMH to be.
Do you have an existing chimney?
So many questions and so many choices.
Give us some info and we will help guide you to a successful RMH build.  




Thank you for your help Thomas. Im not sure whether  to go with an 8" or 6" version. The stove would be located in Our living dining kitchen on the ground floor of Our home. This floor has around 90m2 but benefits from being quite open plan

Ive been researching the Bell system since you have told me about this and i like this idea which would cut down on the expense of stove pipe.

I would like to use the Bell as a bench and ive heard that its possible with a Bell to use a 6 " system and Get similar heat output to that of the 8"

Also we would love to see Our fire so a batch box is desirable for us

We currently heat our place with a wood gassifier which is linked to buffors which heat the under floor heating. The rmh would serve as a backup in the Fall and early spring when its still not that cold (it gets down to - 20c here)

What drew me to the heaters was the fuel efficiency. I spend a lot of time currently chopping, stacking and moving wood so i would appreciate any possible relief from this.

My main concern which i cant get my head aroind is how the riser barrel attaches to the flue pipe.. Is a hole cut close to the bottom and the first section of flue welded?

Are there any plans you could recommend for a beginner Such as myself who is new to making a stove? I would like something really idiot proof and specific.

Ive taken pictures of local dirt avaliable.. Problem is that here the earth is very sandy but i do have Access to many rocks and used bricks as well as building rubble. My main issue with the stove pipe is cost. Its expensive here to get the 9 meters requires in an 8" version thats why i thought to build the flue from brick. Im Just not sure if this will be effective either though because even when i burn a full Day in my exsist ing chimney its still only warm to the touch.

We have one chimney which is in an awkward position because its away from the cental area of the house

Ive included a picture of the local earth which looks like red Sand

Thank you
IMG_20220904_175200.jpg
[Thumbnail for IMG_20220904_175200.jpg]
 
thomas rubino
rocket scientist
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Hi Robert;
In my opinion, if you are building a J tube then 8" is the way to go.
It burns longer and takes larger wood than a 6" J tube.
If you are building a batch box then a 6" is plenty.
7" and 8" BBs are very high outputs and more suited for large areas.
Not all batch box doors have a window in them. Quite a few have no window at all.
Even when they do it is a smaller window, my doors have a 3" round window.
The "Pisla" cast iron door has the largest window.

Can you source sacks of fire clay?   (Masonry supply house)
What about 100# sacks of commercial medium building sand? (home Depot)
You're going to want both.
When you build an RMH you need fireclay/sand mortar in the "core" area as concrete will not hold up.
When building your bell you can "If you must" use concrete.   Much better to build with a clay sand mortar.

Now let's move on to your "horizontal transition area"
I'll start by saying that if you build a bell design, there is no transition area.
With a bell, you may or may not even use a barrel. Your riser will vent directly into the bell.

Traditionally with a J tube, the riser barrel sat on top of a half barrel.  
The start of your horizontal pipe was attached near the bottom of that barrel.
Much tin snipping and shaping was required.  (Pain in the Butt)

When I'm building a J tube design with a piped mass.
I enclose the sides of my firebrick core with red clay brick, my riser barrel sits on those walls, and the back 1/3 hangs open.
I create a mini bell from bricks below the back 1/3 of the riser barrel.
A horizontal pipe is connected to the mini bell and then runs thru the mass.
I have found this to be much easier than the barrel method.

You can use a bell with either design, they are not just for batch boxes.
Converting an 8" J tube to a 6" batch later is easily accomplished.











 
Robert Grantham
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thomas rubino wrote:Hi Robert;
In my opinion, if you are building a J tube then 8" is the way to go.
It burns longer and takes larger wood than a 6" J tube.
If you are building a batch box then a 6" is plenty.
7" and 8" BBs are very high outputs and more suited for large areas.
Not all batch box doors have a window in them. Quite a few have no window at all.
Even when they do it is a smaller window, my doors have a 3" round window.
The "Pisla" cast iron door has the largest window.

Can you source sacks of fire clay?   (Masonry supply house)
What about 100# sacks of commercial medium building sand? (home Depot)
You're going to want both.
When you build an RMH you need fireclay/sand mortar in the "core" area as concrete will not hold up.
When building your bell you can "If you must" use concrete.   Much better to build with a clay sand mortar.

Now let's move on to your "horizontal transition area"
I'll start by saying that if you build a bell design, there is no transition area.
With a bell, you may or may not even use a barrel. Your riser will vent directly into the bell.

Traditionally with a J tube, the riser barrel sat on top of a half barrel.  
The start of your horizontal pipe was attached near the bottom of that barrel.
Much tin snipping and shaping was required.  (Pain in the Butt)

When I'm building a J tube design with a piped mass.
I enclose the sides of my firebrick core with red clay brick, my riser barrel sits on those walls, and the back 1/3 hangs open.
I create a mini bell from bricks below the back 1/3 of the riser barrel.
A horizontal pipe is connected to the mini bell and then runs thru the mass.
I have found this to be much easier than the barrel method.

You can use a bell with either design, they are not just for batch boxes.
Converting an 8" J tube to a 6" batch later is easily accomplished.



Yes i like the idea of the 8" jtube within the bell combination. Do you have any guidance as to how big the bell should be?

Also is it ok to use a single layer of standard bricks for the bell?

I was thinking of two possible scenarios.. To include a metal cooking plate on top of the bell and perhaps also that it could act as a place to sit on.

My main issue is that i dont have a plan to go off and im not too confident to Just eye it up and build without the experience. Are there any place i could get free plans for this sort of stove? because cash is really tight at the moment
 
Robert Grantham
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I can get my hands on lots of Sand.. Its not builders Sand because its from the local Sand pit where people Just take it for free. I could easily get a few tonnes of this deliver ed for a six pack of beer. Im not sure if the quality of it but i know a lot of the locals use it to make concrete.

I can also buy stove cement for laying fire bricks. If this is what you meant? Mud and metal barrels are also fairly easy to come by. Bricks i can get second hand.

I like the idea of the bell more because the stove piping is expensive as hell here
 
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