We finally decided to go ahead and rebuild our second rocket stove (the one in the living room). My primary wishes were to rebuild the core (better) and to convert the relatively useless mass into a (small) bench. Iulia decided to make it a workshop and … 3 interested people showed up.
During the first day we settled into being together. I left the existing rocket mass heater in tact so we could review its shortcomings together and learn from that. We talked about the basic workings of a rocket stove while talking about the existing stove.
… and then we took it apart:
We had only one wheel barrow of waste which was non-toxic and we dumped it as back-filling at the earthbag cellar.
Though there was some soot in the rocket (sometimes it didn’t burn completely clean) there was very little of it given that it worked for 6 winters. There was a 1cm layer of light and fluffy ash sitting at the top of the heat riser (accumulated over the same period of time).
Until we reached the brick platform upon which the rocket was built.
We then layed out the expansion of platform for the new rocket.
… and started building it … giving everyone their first experience at working with mortar and laying bricks.
The next morning we finished it!
With the platform done we built a mockup of the core (while learning about dimensions and sizing using standard brick sizes) and its place on the platform (and relationship to the bench).
We then settled into a rhythm in which two people were laying bricks (one working on the core, the other working on the bench) and two others were preparing soil for mortar and cob (and doing other support tasks such as cleaning bricks so that the brick layers could work smoothly).
As the chamber that is under the bench started to take for, I figured out how we were going to close the top of the chamber (close from the chamber that makes the bench. The plan I came up with involved recycling two concrete slabs we had lying around together with some bricks. Next I had to figure out how to create a structure that could support that top while allowing a good flow of gasses through the chamber itself. It was a bit of a puzzle but we solved it.
… and the core was rising up
… and the chamber was rising up … and we were starting to apply cob (especially on the back side where access would become more difficult as the construction grew):
… and I think this is where we finished up on day 2:
On day 3 as most of the riddles were behind us and everyone had a better sense of the materials and the work, progressed flowed and accelerated. The core was completed and the chamber layout finalized. While the chamber was being closed up the heat riser was growing.
Pretty soon we were insulating the core with perlite in a clay slip (recycled from the previous rocket) in the chamber built around the core:
… and then the insulation sleeve around the riser was put in place (recycled from the previous rocket) … and also filled with perlite:
… and finally the barrel came on (for the last time – we had quite a few fittings), we sealed all around it with cob … and lit the stove … and despite adverse conditions (a new rocket filled with moisture, on a warm summer day) we all smiled when we saw the flames getting sucked into the rocket and the dragon came to life. Very soon we were in an overheated room with a warm bench (that nobody wanted to sit on).
… in the excitement (and a bit of rush to accommodate the schedule of one of the participants) I missed taking a picture of the barrel on the “raw” rocket … but the next day (today!), with Liam’s help preparing soil and mixing cob, we were able to get much of the cob work done (and we may complete the rough structure tomorrow).
Even though it is using the same floor area as the previous rocket, the footprint of the new build is much larger … and it dwarfs the room … which feels a bit off. That is a price we’ve paid for having a warm bench to sit on (without taking on a much larger renovation).
It was an intense weekend. I’m glad to have had an opportunity to share rocket stoves with Tudor (missing from the picture below because he had to leave before we took it) , Dan and Liam and Iulia. I’m glad to have a good core with hopefully a comfortable bench for next winter.
It’s time to try a next step – we are going to rebuild the one in the living room, this time we are going to make it even more efficient and add a heated bench for two on it :).
We are open to make it as a mini-workshop where you can come over and learn by doing.
The workshop
We will be building a rocket stove with a small mass attached to it and a place for sitting / reading / resting. It will be an opportunity to learn what were the limitations of the previous design (and why they were introduced in the first place) and the considerations that went into the new design. We will be building a typical rocket core with an attached brick chamber with some cob to add more mass and bring it altogether. It is a tight design that will fill a tight space.
You will have an opportunity to:
Learn about rocket stove design,
Participate in all stages of construction,
Meet the materials and the tools involved,
Spend some time at and learn about Bhudeva.
All within the settings and limitations of a traditional Romanian village house.
The build/workshop is estimated to take place in 15-17 of June 2018. The workshop time is Friday (half day), Saturday (full day) and Sunday (until 16:00). If you’ll join us, please arrive sometime Friday until 13:00 (so we can have the second part of the day for working).
There are 5 places available for participants. Sleeping will be in tents (there is plenty of space). The price for the workshop is 540 lei / participant. We are asking for 200 lei in advance (bank deposit or transfer), when registering, for booking your place. The rest will be paid cash at Bhudeva.
Please acknowledge that English is the communication language at Bhudeva.
Living conditions
We are assuming you will want to stay at Bhudeva, however there may be other options one of which is a new pensiune just outside the village (a few minutes drive) which has recently opened its doors to visitors.
If you do choose to stay with us, here are a few things you may wish to know:
You will be camping in a tent (that you need to bring with you). We do not yet have built structures to house other people. We have one small house which is a private space and we prefer to keep is that way, for now.
We have one composting toilet in the house. If you stay here for a few days or more, you will learn not just to use it (make contributions) but also learn to care for it (emptying it in our humanure hacienda).
We have a small outdoor kitchen. We are inviting you too cook together or, if this doesn’t suit you, please bring your own food. If we will cook together, you are invited to bring with you some of the next produce: “bob lung” rice, spaghetti pasta, avocados, honey from verified source (we’ll coordinate this by email).
We eat mostly vegetables and fruits, with some dairy productions and eggs. Most of it locally (in the village) produced.
We intend to be doing everything together: working, cooking, cleaning. We’ll see how this flows.
If you’re interested to partake please write Iulia at iulia [dot] sara [at] gmail [dot] com… in English and include your phone number and the questions you want to be answered before coming to the workshop (and maybe during the workshop, if you already have something in mind).
As winter set it and the rocket stoves started burning regularly I thought about using them for baking bread … which I do regularly and I thought would be great if I could do without having to use the electric oven. The stoves can be used for cooking but it takes them a long time to bring a medium/large pot to a boil … so I’ve only used them for a bit of partial cooking.
I remembered coming across (I think in the original Rocket Mass Heaters book by Ianto Evans) a kind of aluminum-foil dome that you could put on top of the barrel and use that as an oven. I was doubtful but decided to try making one. I thought about how to go about doing it for many weeks and came up with an approach that seemed feasible.
I built up a wire-frame that was designed to create two layers of aluminum foil (inner and outer) with insulation in between them. I used the commonly available in the village fencing wire … it wasn’t as thick or rigid as I would have liked it to be so I two twisted strands to get it to be more structural.
In these images you can see the continuous foil sheets, the inner layer already creating the dome and the rock-wool insulation going on. It wasn’t precision work … and it took much longer than I thought it would … I think I played around with it for almost an entire day.
I ended up with something pretty fragile, funny looking … and honestly … discouraging.
The structure wasn’t precise or solid enough to create a good seal with the top of the barrel … I didn’t think it could hold a temperature that could bake bread … and I just set it aside.
It took a few weeks until I decided to cook on the stove and to cover the pot with the aluminum cap. WOW … the pot came to a boil very quickly. I was surprised. I decided to give baking a chance … and boy did it work. The first couple of times I burned the bread a bit. I also ruined one of the silicon baking trays (and weakened the other one) because I placed them directly on the barrel top … and it apparently reaches a temperature much higher than what the silicon is designed to handle. I now place two flat (half) fire bricks on top of the barrel and the baking trays on top of them.
I now do a lot of cooking on the rocket stove. It takes some planning in terms of timing … for the cooking to coincide with the burning of the stoves. But with a bit more attention and intention a lot of the cooking is now done on the rockets. Pizzas are also now made on the rocket … much faster … tastier … and no electricity needed:
Mamaliga goes on the rocket in small clay pots (that hold personal servings). Melted cheese on bread goes on … and more and more. There is a journey of discovery … what should be put directly on the surface, when to use bricks, etc … but the electric oven has been used very little in recent months. The gas cooker is also working much less. It is satisfying to be able to harness that is already there (and would otherwise rise to the ceiling) instead of expending (and paying for) more energy.
It works based on radiated energy. The aluminum foil reflects radiated heat back down onto whatever is cooking under it. It also locks in some convective heat (hot air rising) … I don’t know which is the more significant source of energy … I suspect the radiated.
One “problem” with the aluminum cap is where to put it when it isn’t used. Then a few days ago I had a thought … if the aluminum reflects radiated heat then couldn’t it reflect that heat back into the room. I went to the workshop and came back with a scrap copper pipe and used it to prop up the aluminum cap so that it reflects heat towards the couches in the room:
… and that works too … really well … a very noticeable effect when you are sitting in the beam of heat that comes from the dome. I still need to bring in the copper pipe cutter to cut it down to size so that it can be supported with the edge of the barrel instead of projecting all the way down to the cob indentation … but it works.
What started out as a disappointment has turned out to be a really useful winter tool and upgrade for the rocket stoves 🙂
It was on my mind for many months … rebuilding the first rocket stove. It worked good – though not great. There were some design errors and compromises and during the last winter there were more smokeback events that I could not explain. I wasn’t keen on taking apart something that (kinda) worked and embarking on another build project. So I played around with it in my mind for a long time. Eventually I had a design I felt comfortable pursuing, I did a simple cob test to confirm the materials I had … counted and purchased bricks … and decided to go for it.
At the last minute I decided to give it a chance to become a workshop build and so I published an invitation and sent out word to people I knew and thought may know other people who would be interested … this was 3 or 4 days before the planned weekend build … and once person did sign up … making him the first participant in the first workshop I have ever offered at Bhudeva. I had two pairs of helping hands – Annelieke and Horatiu.
The project was born when I did created this layout:
I was able to take real measurements, finalize brick counts … and get confident enough about my vision to move forward. The first thing we had to do was to take apart the existing stove … which was magical … the knowledge that most of the materials can be reused … that the rest are non-toxic and can simply be tossed out anywhere on the land where they will be reassimilated by nature … its one thing to know this and another to experience it:
I was surprised to find the metal heat riser mostly in tact … though it was dry and chipping. Most of the clay-perlite insulation was used in thew new build … which … began by recreating the layout in place to find the exact position it would be in relation to the existing chimney.
With the position fixed we were able to get to work on building a raised floor:
And then, layer by layer, building up the core of the stove:
… and when we brought in the barrel for a first fitting it started to feel like it just might become a real life rocket stove:
In the following image you can see the experimental part of this build. I discovered these honeycomb bricks and decided to use them to easily create heat channels and storage mass. There are two air passages (barely visible in the image) that allow the hot gasses to flow from the barrel into the two-brick chamber on the left hand side of the image – where they flow up. Then (as can be seen in later images) there is a top chamber that allows the gasses to flow across and down the two-brick chamber at the top of the image (right up against the wall) – where they flow down and then out through the chimney. There were three experiment going on: 1) using honeycomb bricks; 2) introducing a vertical flow both with both bottom-up and then top-down flows; 3) and gaining improved heat storage by having mass outside (the shell of the bricks) and inside (the honeycomb pattern).
This is as far as we got in the two days of work we had available. Horatiu and I agreed that he would come back for another day of work during which we will complete the build and fire it up for the first time. So during the next few days Annelieke and I continued doing some preparatory tasks. The most prominent task was the heat riser. Annelieke started doing a perfect and wrong job. Can you guess what is wrong in this image:
Annelieke is doing fantastic work getting the bricks aligned and leveled … but she is laying them without overlaps … creating a beautifully symmetric and unstable structure. This is something I take so much for granted that I did not spot until a few more layers were built and it became very prominent. So It had to be taken down and rebuilt properly:
While she did that I built some insulation chambers around the core (to extend the insulation that would be placed around the heat riser) and started filling them with the clay-perlite mix from the old core … and as you can see in the bottom-left corner I started playing around with cob … hoping for a better experience (I’ve had very poor experiences in the past):
On the day Horatiu came back we finished building up the honeycomb brick chambers and the top chamber in which gasses could pass from the up-flow chamber to the down-flow chamber:
The top chamber was closed with bricks and we then added on the sheet-metal container for the insulation:
… filled it up with clay-perlite insulation:
… and sealed it:
… and suddenly that was it … everything was ready for a barrel:
… and lighting a fire … the smoothest lighting of a new rocket stove I’ve ever experienced … excellent draft (probably helped by the fact that the core had a few good days to dry):
I was then left on my own to slowly transport cob-worthy material, to mix it up in reasonable one-person batches … and slowly build it and transform the stove from something very mechanical and engineered to something organic and mysterious:
There were a few places where seeds apparently got into the cob mix … and given that there was a lot of moisture inside this happened, in a few places:
It now, though still slowly drying, looks like this:
The second lighting of the stove, in contrast to the first, went very poorly. I am guessing it had to do with the loads of cool moist cob. This is where the experimental part may have also kicked in … the gasses may have had a hard time establishing a complete and continuous flow throughout the stove, resulting in serious backsmoke. During the third lighting I was careful to preheat at both cleanouts, to start very gradually and only when the stove was flowing well to put in a full load … and … to my great relief … it ran perfectly again. The fourth lighting was not so good … I wasn’t as patient. Since then I’ve lit it a few more times and it has been going fine.
I estimate that, aside from the bricks, I put on over half a ton (maybe up to three quarters) of cob. Thats a lot of moisture. At the end of the first lighting (before cob went on) when the full load finished burning the bricks at the back were noticeable warm. Not so during the next few lightings. There are many liters of water in there that need to dry. This is something that should be taken into consideration in a construction schedule. I started the construction early so there would be time to experiment and make corrections. I did not take into considerations how long this would take to dry … it still is drying.
Cob was much more friendly this time … finally. I played around with different finishing techniques … I still am. It is a subtle thing finishing and there seem to be numerous paths to go about it. It is very pleasant work (when it works) to be able to mold shapes, smooth corners, add colors. It felt like a complementary and balancing process to the more structured, measured, aligned process of building the core. It felt free, open, secure, … embracing and welcoming. It is a pleasant way to finish a build and a much more pleasant result 🙂
The stove has already worked for a few cold nights. It’s still hard to say how good it works because: its not that cold yet, there is still humidity in the mass, the barrel itself is partly wrapped in cob … so a few things still shifting and changing. I am looking forward to experiencing how it works … both the immediate heating and the heat storage for the night. I have a feeling that it is going to be more efficient in terms of wood consumption (then its predecessor) … I am curious how it will compare in terms of heat storage (the previous stove was all storage, slow to heat up but then radiated plenty of warmth throughout the night – sometimes even overheating the room).
I’ve started preparations for replacing our first rocket stove with a newer, better built, better functioning rocket stove.
I am planning the new build for this coming weekend and have decided to offer this build as a mini-workshop on rocket stoves.
We will be building a rocket stove with a small mass attached to it (not a full bench as in the complete rocket mass heater design). It will be an opportunity to learn what were the limitations of the previous design (and why they were introduced in the first place) and the considerations that went into the new design. We will be building a typical rocket core with an attached brick chamber with some cob to add more mass and bring it altogether. It is a tight design that will fill a tight space.
You will have an opportunity to:
Learn about rocket stove design.
Participate in all stages of construction.
Meet the materials and the tools involved.
Spend some time at and learn about Bhudeva
All within the settings and limitations of a traditional Romanian village house.
The build/workshop will take place on August 23-34 (Saturday & Sunday). There are 5 places for participants. Sleeping will be in tents (there is plenty of space). We will be doing everything together: working, cooking, cleaning. The price of the workshop is 450 Ron.
When I started playing with rocket stoves the main resource available was the Rocket Stove book. Though I still consider it a must read for anyone heading into Rocket Stove territory, I do not consider it sufficient. It left me with many questions, it has some outdated information and some things that, knowing what I know now, are borderline wrong. Fortunately there is now an additional resource that complements it wonderfully.
Earlier this year we participated in two kickstarter documentation projects on Rocket Stoves. I’ll speak shortly about one and at more length about the other. The shortly: the Paul Wheaton 4 DVD pack is a nice to have thing. It was a huge success on kickstarter which made its production value all the more disappointing. It includes 4 DVD’s none of which felt complete and comprehensive (the Fire Science came close). It has low quality video and audio. It was nice to have a glimpse into a workshop with Erica and Ernie which I do not have access to … but it was an opportunistic production. With the funds it raised I felt there was an opportunity to create something much better … an opportunity that was missed. This kickstarter project felt incomplete and … well … icky.
Which brings me to the second production How to Build Rocket Mass Heaters with Ernie and Erica by Calen Kennett of Village Video. This was the first of the Kickstarter projects to launch and though it got fully funded it did not create the buzz that the second project got. It was delivered late (I just received mine a couple of days ago) but that was because loads of caring production work went into it.
It documents an entire build of one Rocket Mass Heater (the one you see on the cover) – an 8 inch system built over an existing wooden floor. It covers very many details which appeared as questions during my two builds and I have not seen addressed anywhere else, covering tools, materials, design, build and finishing. It has excellent quality video and audio. It is a composite of footage shot on site during the build together with a separetely shot and well thought out interview with Erica and Ernie (with excellent quality audio). Inside the DVD case there is a printed page with a list of tools and materials used in the build … superb attention to detail.
The kickstarter edition included Erica and Ernie’s recently published The Art of Fire (which I have yet to take in). In addition there was a surprise on the Kickstarter DVD – the detailed plans for the RMH in the DVD (which more than makes up for one thing that I believe is not emphasized enough in the DVD – an explanation of the basic structure of feed tube, burn channel and heat riser and their dimensions). It is a production infused with care and quality.
If you want to get started with Rocket Mass Heaters I would recomment the (above mentioned) book and this DVD.
Our first (bedroom) rocket stove worked really well … it literally saved us during our first winter here. We did not have enough wood prepared … and it’s super efficient burn-and-battery kept us warm. However there was one recurring problem. The top surface was made of metal. It was intended to both radiate heat quickly into the room and to provide a potential cooking surface. It was also an easy way to cap the brick tower. This metal surface responded to the intense heat of the rocket by warping which in turn placed pressure on the cob seams that sealed it in place … which in turn leaked poisonous gasses into the room. The temporary solution was to keep fixing it and adding more layers of cob to it (which we did all winter long). The long term solution was to replace the top.
I started by modeling the top and I opted to use rebar to support the bricks that would make up the new top. I didn’t want to mess with or work on the existing brick tower so as not to mess up the room (cutting bricks creates alot of dust). So I added half-height layer of bricks and notched it to accommodate the horizontal rebars.
Opening up the existing top was fairly simple since it was already coming apart. I took this opportunity to replace the insulation around the heat riser. When we built it we used ashes (which is all we had) and they settled quite a bit. I scooped and vacuumed out the ash insulation and replaced it with a perlite & clay slip mix (we managed to find perlite in preparation for the second rocket stove). Then a little bit of refractory (heat resistance) mortar and the rocket was fixed.
Later (this was done back in October, I just now got around to posting about it), when we got to work on the second rocket, Andreea added a layer of finishing.
I still wonder if there was an alternate solution, to somehow prevent the metal from warping …
It is almost the end of December and winter is well upon us. It arrived much earlier then last year (we are now experiencing snow and temperatures that arrived in late January last year). I am relieved that we got the second rocket stove done in time … it means this year we can enjoy life not just in the bedroom but also in the living room. We were able to find a barrel which means it looks (and works) more like a standard rocket stove. Circumstances still did not invite building a proper bench for thermal mass. So we opted to build another “bell” like chamber to retain more of the heat inside the space. We also experimented by building a small metal oven into the bell.
Despite a successful rocket construction during our first build, I was hesitant about this second build. While rocket stoves are a relatively simple, do-it-yourself technology, they do require a certain level of precision and accuracy in design. I am not really worried about efficiency (it’s so much better then standard stove technologies – that you really can’t go wrong with it. I am worried about smoke and poisonous gases leaking into the room. Two things can prevent that (1) a proper design (proportions of different elements) and (2) good finishing. I have proper design pretty much under control. Finishing was, and continues to be somewhat of a mystery. Our experiences with cob and earth finishes have been … well … mysterious. We are still not confident about it.
I was able to delay the project itself by two preparations that needed to be made. The first was to build some kind of small platform on wheels that would enable me to get the existing metal stove out of the way. Though this picture comes later in the time-line … this is the platform in action. Due to two wheels with brakes I was able to get the metal stove onto it and out of the way on my own (though the story of getting it out of the house took a funny turn):
The second preparation was to prepare the barrel. First I had to cut it open and then I had to burn the paint off it (so that no poisonous paint fumes would be emitted from it as it got hot on the rocket stove):
Because of my hesitance I started the project slowly, giving myself time to get back into the “rocket vibe” and to explore what I wanted to build. It began with a rough model that was constructed in the garage. I completely took apart and rebuilt the model a few times over many weeks. I spent quite a bit of time staring it, letting questions appear, letting solutions appear, moving parts around … I took my time with it … until I had a reasonable model … and restored confidence to start actual construction. I lit the model once to check for good draft … but given its design (round barrel meets square bell) it was kind of pointless since it was difficult to temporarily seal.
When I took the model apart I took a few images to document the different layers. I used those images to recollect and reconstruct dimensions during the actual construction. The construction began with a “subfloor” upon which I could build the floor of the rocket itself. The subfloor is built with mostly used adobe bricks. There are two ash-pits (the one in front and on the right is just under the feed chamber and the one on the left is under the future chimney exit) which are built with firebrick.
The floor itself is made of half-thickness firebricks.
Then came the first layer of the core. Though at the end of the day I decided that this would create a burn tunnel that was too deep so the next day I ended up taking apart most of what I built the previous day and removing this layer.
So this second layer was actually the first layer of the burn tunnel (though the picture still has the above pictured layer before I took it out)::
… and then on with the core including a (this time) brick riser (the oven is just set in place to measure precise location optimized for brick sizes), not yet built in):
… then a test fitting of the insulation container – rounded sheet metal tied in place with thick wires:
… and then a test fitting of the barrel itself:
with the core complete it was time to start building the heat-storage bell that contains the oven:
I then realized that it would be easier to continue building up the bell with the barrel in place (so that the quirky round-square meeting could be properly built). But to do that I had to first put in the insulation. The insulation is a mix of perlite and clay slip. It went all around the heat riser and almost all the way around the burn tunnel (no insulation was put in on the bell side of the burn tunnel).
All insulation openings were then sealed with a thick clay (cob-ish) mortar to keep the light and airy perlite from flying around.
Then it was time to complete the bell walls.
… and a concrete-slab we had lying around (of which there are more) was placed on as a cover (it was already fitted in place in the model) providing a lot of thermal mass (it was very heavy – a job for two) and an easy solution for bridging the wide opening of the bell:
The last part that was built was the ash collection pit/chimney exit chamber (on the left):
A few more cut firebricks were used to close the gaps between the barrel and the bell … including the installation of another clean-out opening that gives access directly to the passage-way between the two. Then all that was left to do was to seal all the opening with cob:
and install the chimney:
… and we fired it up and it worked like a charm. The immediate heating effect is new to us (in the first rocket we built where we didn’t have a barrel to radiate heat it takes time to heat up on the inside before that heat is radiated into the space. With this one the barrel gets hot within minutes (with still just the initial kindling wood burning) and quickly becomes too hot to touch. The room it was in was very cold since we had not heated it at all this season. We had a little smoke during the first firing (natural since the entire stove core is cold and damp) so a window was open … and the door to the entry hall was open and the hall itself was open to the outside … and still there was a very fast and noticeable heat throughout the entire space.
I never get tired of watching a hissing fire fire get sucked into the burn tunnel:
Then came the finishing stage. Despite numerous soil composition tests we seem to have ended up with cox mix that was clay rich. We were starting to run out of time (=running into extra cold) and drying the cob takes a good firing up of the rocket over two or three days … so I decided to risk it and applied the cob to the entire stove. Being clay rich meant that it contracted a lot … leaving a lot of cracks … which we could have dealt with … but is also pulled away from the body of the stove itself … and fell of in large chunks.
This is Ricky (in one of her winter outfits) making good use of the straw-bale we used to create the cob mix:
So we ended up pulling it all off and creating an alternate mix … a formula we learned of when we re-finished the north wall of the house. The base was a different clay earth … very sandy (10-15% clay and the rest a fine silt). At first we added to it gypsum as a binder (instead of aiming for a more precise clay-betonite mix). The resulting mix dried way too fast, so we added to it some hydrated lime to slow the drying. We ended working with a formula of 1 part gypsum, 1 part lime and 4-5 parts sandy clay. It gives a hard finish that had much better adhesion and seems to be heat-resistant. It did crack a bit, but that did not compromise adhesion. We will probably try to add another finish coat and maybe some color to it in the spring (all the soil is frozen now).
Initially we had to keep the rocket going for longer periods to really drive the freezing cold out of the room and the walls. The more regularly we use it the less we need to keep it going to enjoy a warm room. When the room is already warm it takes one feeding of the rocket to drastically boost the temperature in the room. It is crazy efficient.
It works amazingly well (to my surprise) as a cooking surface. The only limitation is that you can only cook on it when there is wood burning inside (and for a short time after the fire dies … while the barrel is still hot enough) which, because it’s really efficient, is not a lot of time. So to use it we need to consciously plan to do our cooking while we light and feed it.
The oven in the bell does not work. The rocket is so efficient in heating up the space that it simply does not run long enough to heat up the bell enough to get the stove warm enough to be useful. That’s the nature of this super-efficient stove!
There is more to be said about its performance, but that will come in a later post and after we’ve had some experience living with it. So far we are very happy 🙂
If you are reading this and interested in the technical aspect of Rocket stoves you may want to scroll down to the last part of the post where there is a description of what we actually built. But first, I do will indulge in some personal reflection about rocket stoves.
What is a Rocket Stove?
If you’ve never heard about rocket stoves, though I’ve mentioned them before, this short video is the place to start. This video drew me out of the theoretical reading and into action – anyone can experience the wonder of rocket stoves by recreating what is demonstrated in it:
A rocket stove mass heater is a more elaborate stove built around this concept … it is simple to build, efficiently burns wood – the rocket part (more then most existing stoves) and equally effectively stores and radiates the generated heat – the mass part.
Learn to build one with the one and only rocket stove book
Visit the rocket stove forum (lots of hands on information and helpful people)
Of course you can and should search the Internet and find plenty of information about them.
However if you want to build one I strongly suggest you get the book – there are a few core details that you have to get right – once you get those down you can play around with it a lot. Though there is plenty of freely available information you will be hard-pressed to find all these core details without the book – at least that’s been my experience.
On to our personal rocket story
A Screeching Halt
Last year, as we were in the process of purchasing the land we currently live on, we were also working closely with our friend and architect on designing our hemp-built house (much more on that in coming posts). He designed a beautiful (and functional!) house, but the more beautiful it got to be the more I began to question its economic feasibility = I didn’t think we would be able to afford to build it. We were really committed to the process and invested much effort and resources in pursuing it (including a visit I have yet to write about to the UK to consult with an architect experienced in hemp construction).
As we were working on our rocket stove it was Andreea who insightfully recognized the point at which our beautiful house came to a screeching halt. We were doing some financial planning and were inquiring with our architect for some input on the house systems. We were sitting in his office discussing options for a house heating system – seeking a rough budget to plug into our calculations (which were already looking grim). He picked up his phone and called a fellow engineer. The conversation resulted in a mind-blowing figure ouf 15,000 euro (half of our target construction budget). We realized that something was not right – we felt that the architect and the engineer lost touch with us and our wishes. Further inquiry into the subject brought the figures down to 7,000 euro – still a lot of money and out of our budget.
Though the project continued to move forward and is still alive though dormant today, from that point on it was winding down. Our wish to have a comfortable and warm home, it seemed, could not be fulfilled within the budget we had.
Preparing for Winter
By the time we moved out it became painfully (at the time) clear that we would not be building a new house this year and that we would probably be spending a few years in the existing traditional Romanian village (cob) house. So, we began a long and ongoing (though definitely coming to a first end) effort to fix it up.
The house has a small hall, a small pantry (we converted into a bathroom) and two rooms. One room has a traditional Romanian wood-stove (the other had nothing). We had lots of plans to do lots of things. Though we did lots of the things, many were not in the plans and most of the plans did not reach execution. Our plans did not include building a rocket stove this year. They did include buying a second stove and a third wood-burning boiler.
Then, we discovered the (above mentioned) 16 brick video, we purchased some firebricks and tried it out … and it worked fantastically. We used it quite a lot for cooking outside.
At one point, just for the fun of it, I even built up around it and simulated a rough rocket stove . I used the parts of an old wood-boiler for the heat riser:
Seeing the horizontal burn for the first time was a magical experience:
And then when I placed a barrel on top, it got really warm really fast:
Then came the two+ weeks of non-stop cooking during which we made loads of winter preservations. We were practically living next to the small rocket stove outside. Then when we moved indoors in the evenings to escape the cold and complete the jar preservations we would light the wood stove. It was painful to see how much wood this stove consumed (and continues to consume) compared to the 16 brick rocket stove outside. Everyday I would have words of awe about the outside rocket stove and complain about the wood-greedy stove inside.
Slowly I gathered the courage to suggest we try building a rocket stove instead of buying another wood-guzzling metal stove. And so it began … from here on it’s going to get a bit technical.
Constraints
There were a few constraints shaping this project for us:
Timing – we had already finished putting in wooden floors including a corner of ceramic tiles in each room to house a stove. We did not feel inclined into removing parts of the floor to install a cob-bench (the mass part of the rocket where heat is stored) and we were not keen into working with cob as it takes time and experimentation … and we already had quite a bit on our plate. So we were going to build a stove without thermal mass … making it’s heating efficiency questionable.
Barrel – This is going to be a recurring theme here at Bhudeva – but finding used/2nd hand anything is much more difficult here in Romania then in the USA, UK or other western countries. This is especially true in villages where everything is used, reused and used again, often beyond the point of efficiency or even safety. A key element in the rocket stove is a metal barrel – and for many weeks (which delayed the project) we couldn’t find one. We finally decided to build a rocket stove with “firebrick chamber with a top metal plate” instead of a barrel (we have since found and purchased one used barrel and have a few more lined up … we will keep them stored for future needs).
Insulation We also could not locate (at reasonable prices) any of the suggested insulation materials for the internal combustion chamber – we ended up using wood-ashes – they may not offer the same level of insulation and they may settle over time but this is what we had available to us.
Size – the actual stove – where all the burning takes place is a systemically and purposefully twisted path which, from a certain point early in the path (the horizontal burn chamber) must not become narrower. This is to prevent smoke and dangerous gases from returning into the room – the stove generates a powerful draft and nothing must impeded that flow. The traditional Romanian stove configuration is for a 12cm chimney flue – which is also the size of the chimneys usually built into the walls. Since we did not want to make a new opening in the wall for a chimney we had to adapt to that limitation. This is when rocket stoves designs are suggested for either 15 cm (6 inch) or 20 cm (8 inch). This meant a smaller scale and tighter design and indeed everything was scaled down accordingly. However, in retrospect, given that we built a spacious “brick barrel” as thermal mass – which slows the flow of gases before they exit, I believe we could have gone with a larger dimension in the stove with the limited 12 cm exit flue.
Model First
Like most of the good recommendations in the book, building a model of the stove is an important stage of work – and, as recommended, it should be done on a level surface (I tried to cut this corner and it was a waste of time). To that I would add that it should be built somewhere where you can (a) work on it over a period of time; (b) light it; (c) keep it out of the rain or other wet elements. I built our model in a corner of our barn which answered to all of these criteria – and luckily so because we went through quite a few iterations.
I actually used such images to document my progress of the layers (both as I built them up and took them apart) in building the actual stove in place. There were many small details and the images unburdened my memory and were very useful in actual construction. I spread construction sand on the floor to level it. This is the first floor level model (it changed later in the process) … it is designed to raise the rocket off the floor and create ash collection both under the feed chamber (right) and at the exit flue (left).
On top of that came the “floor” of the rocket itself – intentionally adding more depth to the ash collection chambers.
Then of course the burn tunnel
… and off we go – and you can already see the fire climbing up the feed chamber (the feed tunnel is not yet built up):
The model worked OK. The biggest problem, and one that carried over to the actual stove was the fire crawling up the sticks and out of the feed chamber. I now believe that the cause of this was that the feed-chamber and ash-clean-out beneath it were not sealed properly. So the stove instead of sucking air down from the top of the feed chamber was now also sucking air up from below which both lowered the intensity of the down-draft AND provided an alternate up-draft.
Also, if you decide to build something not quite by the book be prepared to take risks – as not everything can be tested (simply) in the model:
When I built the model I realized that I could not seal the brick chamber nor the top metal plate to the bricks. This meant that we could not assess how effective the generated heat would be contained and radiated from the stove.
Though the top metal plate (can be used for cooking) heated up rapidly it had a surprise for us in the actual stove. The heat generated by the rocket is so high that the metal (5mm thick) warps … the corners fold out creating stress on the cob that seals the plate to the brick structure beneath it. The cob has cracked numerous times (and let out poisonous gases) and we have had to reseal it (simply applying another coat of clay-slip)… it looks like we have reached the point where it is properly sealed – though only time will tell – we check it regularly.
Our Stove
The following images depict the actual stove in construction. First a simulation of the base layer to get its position in the corner. Next time I would try to leave more space between the rocket and the walls to make it easier to access and install the chimney parts – it was a struggle.
Then a little messier with the clay-sand mortar to keep things in place:
In the middle layer (top image) I installed a metal grail to support the feed chamber and let the ashes fall – I notched (with a grinder masonry disc) three parts of brick to support the grail itself:
Then a metal heat riser (used pipe cut to size at a metals shop in Cluj) went on:
and over that went a piece of sheet-metal tied into a roll and then filled with wood ash
Starting to look like a rocket stove
Here the heat riser is sealed with the clay-sand mortar mix
Here you can see that the heat riser is positioned away from the center of the brick box. One reason is that I assumed that the brick-barrel would behave like a steel barrel does and that the wider space would heat up more/faster then the narrow space – so in this case the wide space facing into the room. The space from the other (left hand side) wall is determined by the location of the ash-pit and exit flue (in the dark area at bottom left of the image). Though I don’t know if this actual works – I preferred to have the gases “linger” in the box rather then get pushed out by making the space near the exit flue narrow.
The almost finished stove with a completed brick chamber (I decided to use refractory cement which has adhesive function for the brick chamber instead of the sand-clay mortar which has no adhesive function it simply keeps the bricks from moving and when fired solidifies into a brick-like material) and metal top still undecided feed chamber, a temporary chimney leading out the door and to the hall, a small pot of water heating up and Andreea checking something out (and providing you with some sense of scale).
We still had smoke-back and fire climbing up the feed chamber … which frustrated me greatly … until Andreea intervened with a bit of feminine surrender and wisdom and suggested we let go of the vertical feed and go with a front feed … which not only worked but demonstrated that the stove had excellent draft with absolutely no smoke-back. Here you can see a fully loaded feed with fire swirling into the stove and absolutely no smoke coming out:
Then Andreea took over the clay plastering. It failed miserable the first few times – the plaster cracked and fell of in chunks.
The third time she (1) added hemp fibers and some acrylic construction glue; (2) wet the bricks thoroughly before applying the plaster; (3) applied it in thin layers and worked it in thoroughly with a wet sponge; (4) continued to moisten and add clay slip as the stove was heated up gradually over the next two days.
The chimney winds through 3 corner bends (poor planning?) so it was a bitch to install … but we now have a great looking and working kind-of-rocket-stove in the bedroom.
Performance
Before I talk about the stoves heating performance I’d like to talk about it’s other values – at least those that are important to us.
Independence – with no past experience in stoves or any of the specific disciplines involved in creating this stove and with no access to people with past experience we managed to build this by ourselves. It can be built fairly quickly (it takes more time to gather materials then to actually build it).
Efficient and Ecological – when the stove is first fired up some smoke comes out the chimney … but once the heat riser gets hot (very hot) there is no smoke – the stove performs a full and clean burn of the wood. Not only does it fully utilize the energy embodied in the wood (every time you see smoke coming from a chimney imagine waster dollars – all of that is wasted energy) – but it is also ecological since it releases very little pollution (compared to most regular wood stoves). If you were to buy an industrially made central wood heating stove you would pay a heavy premium for “re-gasification” – which is essentially the burning of the gases release when the wood initially burns. With the rocket stove this is an inherent and simply to achieve function (the insulated heat riser gets too temperatures high enough to burn the gases).
Beautiful – you can shape and mold it and make it your own … which ends up uniquely individual and special.
Sustained warmth – the thermal mass (in our case the “brick barrel”) contains all of that efficiently generated heat and slowly releases it into the space instead of letting it escape out the chimney.
It works great. Though we purchased a lot of wood we did not have time or do enough to dry it properly. Fortunately we also have a huge pile of junk wood that we collected from all over the place – that wood, after we cut it to size, is very dry and perfect for the stove. In a regular stove it may be desirable for wood to burn “not too fast” because heat is present only when there are flames (once the flames go out the stove and usually the space, unless it is superbly insulated begin to cool). In a rocket stove it is best to have a fast and efficient burn – the heat is stored in the mass and then released. We are currently lighting it with a few batches of dry wood and then some of the partly dry wood in usually larger chunks of wood. If we were to use only dry wood the stove would probably get really hot (too hot to touch) in 2 or 3 hours. As we are currently running it it takes 4 or 5 hours.
It uses much less wood then the regular wood stove (I can’t say how much as we are not yet setup for measuring and comparing. But more importantly it’s effect on the room is very different. Since we don’t have a radiant barrel (only the small top surface radiates heat immediately into the space) it takes time to warm the space – the other wood stove warms the space rather quickly. But once its warm the space will say warm much longer (again I don’t have measurements for comparison) … but we usually feed the stove one last time at around 10pm and at 7am the room is not cold (though not warm). With the regular stove the room cools drastically in an hour or two – once the fire is out the room begins to cool!
The heat has a different quality in the rocket stove room – it’s hard to put in words. It is a softer, deeper and rounder warmth then the regular wood stove.
It can be used for cooking – doing so requires using either very dry wood (which burns fast and releases a lot of heat) or patience (it is generally slower heating then the wood stove where fire almost directly heats the pots.
Until recently we have had to deal with the metal warping problem. It strains the corners of the cob that join the metal plate to the brick box to the point that cracks appeared and smoke/gas escaped into the room. It has been easy to fix – adding a clay slip – but has required constant attention. Time will tell if this is going to be an ongoing issue or one that we have resolved.
I would have been happy to make it bigger (see above mentioned constraint 4) and to get the vertical feed working properly. But we didn’t have time … it as getting too cold in the room and we still had plenty of work to do to prepare for the winter. The result is a stove that needs to be fed every 20 or so minutes … but that is a small inconvenience we are happy to accommodate.
We are very happy with the stove. It came to life just as the room was becoming unbearably cold. Creating it was a hugely empowering experience. We are very much looking forward to experimenting with it more and eventually incorporating simple rocket stoves we can build and maintain with our hand instead of complicated systems that cost many thousands of euros and place us at the mercy of technicians and engineers and companies.
We had plans to build a second rocket with an integrated baking stove and a thermal mass bench (wood framed!) stove to replace the existing wood-stove, but time did not allow for it. Next year 🙂
It’s been a frozen two days, it’s dark outside and cold is beginning to set – a good time to go and light the rocket so the bedroom will be nice and warm 🙂
I first came across Rocket Stoves a couple of weeks ago at Paul Wheatons friendly website. I still do not grasp completely how they work but I am learning a lot (and asking a lot of questions) … in other words educating myself 🙂
Gasification
Gasification is a word we’ve encountered many times in relation to high-efficiency wood-stoves. Here’s what I’ve been able to understand so far (excluding professional terms which I still have not got down).
When wood is burned some heat is (naturally) generated together with some gasses. These gasses still contain potential burning energy but in regular stoves they simple escape through the chimney. This is both a waste of potential heating energy and a source of pollution. Efficient stoves that include “gasification” create a kind of “second burning” by (1) containing the gasses in a secondary chamber and (2) by insulating the stove, containing the heat and increasing the temperature (the gasses require a higher temperature to burn). The result is much (drastically more) efficient burning and greatly reduced pollution.
The following video demonstrates the “rocket” burning result of gasification:
Thermal Mass
The Rocket Stoves depicted in Paul’s website is based around the idea of thermal mass – which is a fancy way of saying “something that can contain lots of heat it and slowly radiate it back into the space”. This can be a couch or a wall or even a water heater.
This idea of thermal mass is well known here in Romania. It is used in typical tera-cota village stoves where the heat is directed in a maze of passages that cause the stove to slowly heat up and then stay warm for a long time (a good stove can be lit in the evening and will still be warm the next morning).
At first I assumed that a thermal mass was an inherent part of the rocket stove. But that isn’t necessarily true. This next video demonstrates a rocket-stove used as a cooking stove:
More information and plans for this kind of rocket stove can be found here.
This application of the same rocket stove burning mechanism shows an insulated burner that is designed to keep the heat inside and direct it to a cooking pot. I think this can be a useful design for a cooking stove that can be used during the summer months because it doesn’t radiate unwanted heat into the space.
Water
One of the first ideas we played around with was using the same stoves for both heating the space and heating water. Though this can work it needs careful consideration. Though it’s tempting to think of the stove as heating the water, it’s useful to remember that as this happens the water also cools the stove!
If you add a water heating coil to a traditional Romanian tera-cotta wood stove it will heat the water, but the stove itself will cool down much faster and will have less effect on the space.
It’s empowering to slowly peel away the layers and connect with the common-sense behind heating systems. It makes me wonder about sophisticated technology vs. simple concepts. On the one hand gasification looks so simple to achieve and yet modern central wood-burning heaters, it seems, cannot achieve gasification without electricity!
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