Overwhelmed by RMH info and don't know where to start

We've bought a stone ruin a week ago and want to use Rocket Mass Heater in our tiny home.  

Having discovered the world of RMH I introduced the concept to my husband and we are now both on board.  We were considering underfloor heating and a wood burner.

We want to limit the artificial building materials so I am hoping a RMH will do the trick.  Ongoing we want to save on the amount of wood burnt and have an abundance of olive tree twigs that get burnt up during olive picking season.

I've listened to many many podcasts on this topic now and watched youtube until I've run out of data and bought the not-DVD RMH set and we are 4 hours into watching it.  The problem is hubby is severely hearing impaired and I can't enable the captioning facility so I am having to tell him what is being said.

However, we are starting to feel that we are too stupid to be on this ride. (a touch of self-pity :-))  I need to find the relevant information, distill it and pass it on to my husband.  15 years ago he built us a traditional brick home and used to be an electrician so is a skilled handyman.  Me? Not at all.  I do the research and introduce husband to these crazy ideas.  You should have seen his initial reaction when I told him about 7-foot vegetable beds.

Where should I start?  Perhaps if I lay out some specifications (spitball) for our project someone who has the time might be kind enough to give us some pointers.

End goal
* Heat a stone building with an area of 35 meters square
* No floor (dirt at the moment) and this can be whatever we need it to be.  Thinking of a wooden floor.
* Not and won't be insulated.
* Built out of rocks will point with limestone mortar.  Has an existing brick extension.  
* Use to heat 3 months a year & dry clothes ( :-)  when temperatures fall to freezing in central Portugal
* Use to heat water needs for 2 people
* Used for cooking
* No budget - will scrounge and scavenge required material

I imagined we might be able to run 4" tubing right around the inside of the building almost like a raised skirting board to heat the building's stone wall?

We want to experiment with our first RMH outside in an outdoor camp/kitchen set up and this could be cob (but we have access to pebbles).

Prefer the pebblestone style over the cob style.  Our natural material in abundance is pebbles.

In the future use RMH for extending the growing season by bringing on seedlings earlier in the season.

Hi Jenny;  Big Welcome To Permies!  And another Big Welcome to the fascinating world of rocket science!
What a cool little stone "ruin" you have there!
I think we can help point you in the right direction to become a rocket scientist!
Question; Do you have a copy of the RMH builders guide from Ernie & Erica Wisner?   If not it might be a good investment for you.  
Question; Are clay bricks available?  What about heavy firebricks?

You have the basic information, now we need to make it practical for you.
You wanted to start outdoors with a cooking J tube?  This is a great idea!   Better to learn outdoors. Before building indoors.
Can I assume you know the proper size to build a J tube?   A 6" to cook on is plenty. If you are wanting a bench to sit on then I would build an 8" J tube.
Mass;  Pebbles work ok for a quick build but do not hold heat like a solid mass.  So I recommend a cob / rock filled bench.
Cob;  Don't let it scare you... it is nothing but sticky mud.  In a mass, after you place your horizontal pipes. You cover them with "cob" mud... then use as much larger solid rock.  Bedding then in with mud so there are no air spaces.  
So as you see the Cob is only a filler, and can be used as a final covering if desired. The large solid rocks are your heat holding medium.  When using pebbles one might think that rock is rock but it is the air spaces between those pebbles  that make them less desirable than solid rock bedded with mud.

I'll stop now so I don't overload you with information.
Write back with your answers and questions.
Our happy crew of Rocket scientists are eagerly awaiting your questions!

Hi Jenny;    While reading your post again I wanted to point out one more thing.
I'm afraid you can not try to heat those stone walls!   Your inside mass must be spaced away from the stone and Ideally some form of insulation between them.
Why ? You might ask...   If you try to heat those walls, they will suck up any heat and transfer it to the other side (outside).   You can not heat central Portugal with an RMH :-)

If you have pebbles in abundance, you can use those for the mass bedded in cob. Aside from vertical walls or finished surfaces, this thermal cob does not even need to have good clay content; as long as it will hold its shape after drying it will serve the purpose of continuous thermal mass. If you have no access to clay for cob, then brick or stone will serve fine for exterior and structural material.

Running flues under the floor for a warm radiant surface is fine, though dependent on good design to work - there are lots of ways you could mess it up, and relatively few completed projects to base your work on. A bench along the walls as long as it is insulated from the wall would work fine, while reducing the amount of exterior wall to pull heat from the interior.

It looks like your brick extension is a few steps down from the original stone structure. What is the wall between them like? Mostly solid, or any major open space? How thick? Building your RMH in/on/against that wall would probably be your best bet. How thick is the stone wall there? You would benefit from mass, but mass that is more than a foot thick will take days to heat through. This would be fine for deep-winter climates which need heat continuously for weeks on end, but not for a place that needs warmth intermittently. The less constant the heating demand, the thinner your mass wants to be so it can be responsive within a few hours at most.

Hi Jenny!  Welcome - and thank you for spending the time to craft such a complete introduction to you and the RMH questions!

First, listen to Thomas.  He's right. (and Glenn... he got his posts in while composing this!)

Second, yes to the Wisener book.  You need that because its the best source of technical information and will also lead to a safe, solid, balanced stove.

I'll just add that our magnificent overall-clad patron here (Paul Wheaton...) has a simple cloth wall tent (tipi) in Montana that has been successfully heated with an RMH.  The main lesson there is that the bed and bench were integral, so you might consider how to have your bed (or a winter version) that is directly atop the heated mass.

Also note that although RMH builders are famous for scrounging for free materials and using what's at hand, the "core" of the stove (the feed tube, burn tube and riser) have high technical requirements and must be built with appropriate materials and with care for the proportions.

Finally, start small & fail small.  With found & natural materials you can take an RMH apart and rebuild it, so start small & simple and then adjust.

Hi Jenny;  
Peter Berg just gave us this link to a Portugal build.   https://www.facebook.com/BatchRocketPT/

That made me laugh.  And it makes sense. It's liberating in a way as I could do without a weird 3D skirting board right around the inside.

thomas rubino wrote:Hi Jenny;    While reading your post again I wanted to point out one more thing.
I'm afraid you can not try to heat those stone walls!   Your inside mass must be spaced away from the stone and Ideally some form of insulation between them.
Why ? You might ask...   If you try to heat those walls, they will suck up any heat and transfer it to the other side (outside).   You can not heat central Portugal with an RMH :-)

Glenn Herbert wrote:It looks like your brick extension is a few steps down from the original stone structure. What is the wall between them like? Mostly solid, or any major open space? How thick? Building your RMH in/on/against that wall would probably be your best bet. How thick is the stone wall there? You would benefit from mass, but mass that is more than a foot thick will take days to heat through. This would be fine for deep-winter climates which need heat continuously for weeks on end, but not for a place that needs warmth intermittently. The less constant the heating demand, the thinner your mass wants to be so it can be responsive within a few hours at most.

Glenn, the wall between the extension and the ruin is stone (it is the ruin's wall).  The extension is like a lean too against the ruin. We aren't going to break through the wall. We would rather have a veranda connecting the 2 buildings.   The walls in the ruin are over a foot thick.  About 50 cm (1/2 meter or 1.6 ft).  

The ruin is 20 meters square but we will put in a shed-dormer which will sit over the brick lean too and house our bedroom upstairs, which we prefer on the cool to the cold side of things.  The brick lean-to will be built up with a flat roof so we have a balcony.  This means that the ground floor is going to be no higher than 2 meters.  Therefore I thought the placement should be on the wall opposite the doorway and the apex of the building can be used if we need height for the riser.

I've taken note of your comment on responsive heating and responsive heating is more in line with our needs and personalities.

thomas rubino wrote:Hi Jenny;  Big Welcome To Permies!  And another Big Welcome to the fascinating world of rocket science!
What a cool little stone "ruin" you have there!

You have the basic information, now we need to make it practical for you.
You wanted to start outdoors with a cooking J tube?  This is a great idea!   Better to learn outdoors. Before building indoors.
Can I assume you know the proper size to build a J tube?   A 6" to cook on is plenty. If you are wanting a bench to sit on then I would build an 8" J tube.
Mass;  Pebbles work ok for a quick build but do not hold heat like a solid mass.  So I recommend a cob / rock filled bench.
Cob;  Don't let it scare you... it is nothing but sticky mud.  In a mass, after you place your horizontal pipes. You cover them with "cob" mud... then use as much larger solid rock.  Bedding then in with mud so there are no air spaces.  
So as you see the Cob is only a filler, and can be used as a final covering if desired. The large solid rocks are your heat holding medium.  When using pebbles one might think that rock is rock but it is the air spaces between those pebbles  that make them less desirable than solid rock bedded with mud.

I'll stop now so I don't overload you with information.
Write back with your answers and questions.
Our happy crew of Rocket scientists are eagerly awaiting your questions!

Thank you for the warm welcome and all the responses so far.  I feel encouraged and we are going to get started physically as soon as the rainy season ends. It will give me time to get and read E&E's book too.

We will start with a 6" size.  Once happy we will rebuild it in the house and do a bigger 8" one outdoors so we can incorporate the heated benches.

We can get hold of both clay and fire bricks.

The answer is no to the question "Can I assume you know the proper size to build a J tube? " but I have seen a table on sizes on Pieter's site I think.

I see what you mean about using the cob as a filler.  It is rocky in this part of Portugal and we have access to rock not just pebbles.   I take the point on airspace.   The first video we watched was the pebble style RMH in the Fisher-Price House.  

I've never worked with cob but I do tend to be allergic so from what I've read about cob and cob dust I didn't think it ideal for me as I am allergic to house dust {which is why I live in a van ;-D } Also don't know where we could get clay from.  We have only just arrived in Portugal.  We could post out requests on FB forums and on here but getting the clay seems like it would be challenging.  I could harvest bog-standard mud from our Huggie beds we want to make...

Jenny:

Most clay comes from some place in the yard and a shovel!  That stuff works well for cob.  Once of the first tasks is often to dig some holes and do a "quart jar test" to see how much clay is in your soil.  The nice thing about using dug-up clay in cob is the clay is free (as is your labor...), and is generally very low in dust creation!

The clay used in "clay slip" for holding and sealing bricks is often more refined stuff and comes in a bag from a ceramic supply house.  

I don't have a lot of allergies per se, but my sinuses are exquisitely sensitive to dust.  I'm very friendly with my respirator!

Eliot Mason wrote:

Paul Wheaton...) has a simple cloth wall tent (tipi) in Montana that has been successfully heated with an RMH.

Thanks, Elliot.  I'll be getting THE BOOK right away.  

And I've listened to the tipi podcast.  In fact, I use Paul's podcast to drift off to sleep at night (ssssshhhh don't tell him I said that ;-D).

Something that was mentioned in the podcast about the efficiency and ease of lighting the RMH being slightly more challenging if it is as cold outside as it is inside had me worried though.  I want to retain the look of the rocks on the inside so other than lime mortar and roof and floor it will be uninsulated.  

Your ears should twitch a little about "cold starting."  There are some clever ways to improve the cold start, although frequent burns to keep the mass warm is also a good way to deal with it!

A note on insulation ... although the building itself won't be insulated, any bench or mass you build SHOULD be insulated.  For instance, a bench bottom and side facing the rock wall could have insulation or at least a thermal gap, which would help direct more of the heat into the living area.  It will also prevent a direct mass->wall transfer of heat!

Jenny : It is called a bypass gate.   You build it in place and it diverts a portion of the super hot exhaust directly to the chimney.
As your chimney heats the draft will flow and soon your bypass is closed and all the heat  is flowing into and thru your bench.
Here is a picture of the mechanical bypass I sell at dragon tech to give you an idea.  You can home build something that accomplishes the same thing.

If you are not going to open the stone wall to the leanto, just putting the RMH next to that will be good. Without trying to heat the leanto, making that stone mass warmish will be positive all winter. I think you will be better off warming the shared wall than an exterior wall. Two meters is plenty of height for RMH clearances, so you don't need to worry about that. Depending on the details, you may want a heat shield on the ceiling above it.

Jenny;  
Get some cheap clay bricks 25-30.of them.    
A 6" J tube is 5.5 " square, all the way thru.
So your feed tube is 5.5 x 5.5 x 16 " deep
Your burn tunnel is  5.5 x 5.5  with a  10" burn tunnel roof length
Your riser is 5.5 x 5.5 and at least 36" - 48" tall. (6"metal  stove pipe is fine to play with)

Play with one out in your yard. Or just under a roof if its raining.  
They need sealed from air leaks. Any old mud will do.
No barrel over top , just build a J tube and burn it.    Its great fun actually. Figure out how to cook with it. Or just sit and enjoy the warmth on a rainy day.

Peters site would have Batchbox sizes.  
The RMH builders guide will have a complete list of J tube sizes.

Jenny Ives wrote:
End goal
* Heat a stone building with an area of 35 meters square
* No floor (dirt at the moment) and this can be whatever we need it to be.  Thinking of a wooden floor.
* Not and won't be insulated.
* Built out of rocks will point with limestone mortar.  Has an existing brick extension.  
* Use to heat 3 months a year & dry clothes ( :-)  when temperatures fall to freezing in central Portugal
* Use to heat water needs for 2 people
* Used for cooking
* No budget - will scrounge and scavenge required material

Hi, I cannot help with the technical stuff, but some general tips. Maybe one of these you don't already know.

RHM works by overheating the combustion gases, thus making it a more efficient combustion. That makes it burn fast and very hot in the first chamber. The exhaust is used then for heating some thermal mass where the heat can be stored. That's great for a heating, not that much for cooking or hot water. If you want it for cooking, then you have to place your cooking iron (or glass) close to the combustion chamber, so it can be hot enough for cooking, but that will take heat out of the duct towards the room, meaning less heat in your thermal mass storage. The designs I've seen around here have a insulating lid to seal the heat from running outside the kitchen iron.
Matthew Walker's kitchen is using a vitroceramic glass and looks great for cooking, but it might not be as efficient as a heater since it releases much heat at high temperature, not storing it in a thermal mass for slow release.

Heating water for your bath is a completely different story. Unless you are willing to heat water in pots in your kitchen, heating water in a boiler risks excessive water pressure and it can be hazardous. The simple way to have hot water running to your bathtube/shower is to place an unpressurized self-filling water container in the second story that you can heat with the exhaust pipe. In case the water gets too hot, it will produce steam that you might divert to a window, but it will not explode. Being higher than your bath tap water will flow without need of a water pump.

May I ask why you wouldn't insulate the house? If it is because of materials, there are plenty of natural options. Nude stone/bricks is too cold. You may use plaster, wood or even carpets like the castles of old. Air chambers also do good. Insulating the exterior is better for the efficiency, but insultating the interior is better for the looks. Controlling the ventilation is also important, both the size of the vents and their allocation, since having an open vent in the upper wall will let the heat escape, while having the vent in the lower wall will preserve heat (you might need a dedicated chimney for this). A ventilation can be something as simple as a hole with a small handle door.

I don't know if the following is feasible in your situation, but since your house is rather small, I would think in building it like an hypocastus, this is, the exhaust pipe running under the floor. This would require to insulate properly underneath the exhaust so you don't heat the dirt under your house, but just your flooring. Metal can be used to distribute heat throughout the floor, so it does not burn your feet, but rather keep it warm. The biggest benefit is that it would not steal space for furnitures, and you'll feel warmer using less energy. Some hypocastus that are still in use have a sealed door in the floor where the inhabitants can feed the hearth. The hearth is under the house, but it takes fresh air directly from the outside (think of a small cave, with a hearth in the end, the exhaust pipe then running under the house and ending up in the chimney above the roof, people can access this zone by that small door in the floor from the inside). Well, a proper hypocastus might be too much work, but you might modify it to suit a RMH design.

Hi, I cannot help with the technical stuff, but some general tips. Maybe one of these you don't already know.

The simple way to have hot water running to your bathtube/shower is to place an unpressurized self-filling water container in the second story that you can heat with the exhaust pipe. In case the water gets too hot, it will produce steam that you might divert to a window, but it will not explode. Being higher than your bath tap water will flow without need of a water pump.

May I ask why you wouldn't insulate the house?

I don't know if the following is feasible in your situation, but since your house is rather small, I would think in building it like an hypocastus, this is, the exhaust pipe running under the floor.


Hi
Some food for thought.

We considered insulating but from my research we must let the rock breathe.
Also we like the look of the rock.  
Will insulate floor, roof etecetera.

Thanks for your input 😄

Kind regards

By way of update

We have a barrel!! Our neighbour gave us one without knowing we needed one! It's a sign 😁

We've collected a lot of big rocks.

Initially we aren't going to try make this RMH be all singing all dancing.  Are looking at the stairway designs.


Will keep you posted. Thanks all

Jenny Ives wrote:

Hi
Some food for thought.

We considered insulating but from my research we must let the rock breathe.
Also we like the look of the rock.  
Will insulate floor, roof etecetera.

Thanks for your input 😄

Kind regards

You can insulate one side and leave the other for looks/breathe, no?

Abraham, According to heritage houses the best thing to do is to get the walls dry and keep them dry with low constant heating.  This is why I feel RMH in the ruin will be fantastic. A stone over 1/² meter thick doesn't need insulating.

Besides we like the look of the stone 😊 We can soften the feel with decor.

Reference for stone buildings.
https://www.heritage-house.org/stuff-about-old-buildings/insulation/internal-insulation-to-old-house-walls.html

It could be. My experience with heritage buildings is rubble masonry walls (mampostería y tapias). These have a big thermal mass too, but they benefit from plaster. Actually, I think the plaster is needed to keep the wall dry (they are painted with quicklime). In masonry, a wet wall may crumble. Hangover roofs so the midday summer sun don't touch the walls is also something usual in these houses.
All stone walls looks cold to me, but I might be wrong. That's why they put carpets on old castle walls.

Abraham Palma wrote: That's why they put carpets on old castle walls.

We will need a new thread for stone buildings as I have much to learn.  My little stone ruin is probably smaller then a typical castle's privy.