The Rocket Mass Heater Builder’s Guide

This kickstarter was originally planned for last year … its finally arrived. Until now there has really only been one book on Rocket Mass Heaters by Ianto Evans, but having read it and built rocket stoves guided by it, I feel it is out of date (though I haven’t seen the latest edition). There has been much evolution since this book was written and I am confident this new book by Erica (and Ernie) Wisner is a much needed replacement for it.

If you are new to rocket mass heaters and you get to the kickstarter in time (there are a limited number of places available) I recommend the $75 bundle which includes the Village Video DVD – which is the best I’ve seen so far and I have a feeling will compliment the book very well (since it also follows a build by Erica and Ernie). That bundle should give you a very good start towards building your own rocket mass heater.

Cooking on a Rocket Mass Heater (Rocket Stove)

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.

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I ended up with something pretty fragile, funny looking … and honestly … discouraging.

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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:

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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:

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… 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 🙂

 

Split wood with a tire

I saw this video probably a couple of years ago. This year I ordered a new batch of wood and decided to give it a try … and all I can say is WOW! It doesn’t always go smoothly (depends on the size of the wood and tire, knots in the wood, etc.) … but it is always an improvement on hacking in the open. It is especially useful when cutting wood for rocket-stove size … generally smaller pieces than wasteful metal boxes.

The Second First Rocket Stove

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:

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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:

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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.

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With the position fixed we were able to get to work on building a raised floor:

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And then, layer by layer, building up the core of the stove:

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… 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:

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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).

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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:

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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:

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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):

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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:

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The top chamber was closed with bricks and we then added on the sheet-metal container for the insulation:

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… filled it up with clay-perlite insulation:

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… and sealed it:

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… and suddenly that was it … everything was ready for a barrel:

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… 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):

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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:

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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:

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It now, though still slowly drying, looks like this:

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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).

Village Video DVD: How to Build Rocket Mass Heaters with Ernie and Erica

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.

Rocket (stoves) here, rockets there, rockets rockets everywhere

We’ve built two sort-of rocket stoves (red and bell) so far … and they (though far from optimal efficiency) have been magical, pleasant and a godsend to our quality of life (being warm and comfortable in winter). Rocket stoves are simple (but not idiot-proof) technology, built from common and available materials, they are super efficient at burning wood and super efficient at retaining warmth. They are an organic joy to have in a space.

Which brings me to a funny story I’ve wanted to tell. When we were making plans to build our first rocket stove there was a gypsy working for us for a couple of days (he begged for work, and we decided to give him a try, and he stayed for only two days because he rested more than he worked). During his short stay he told us about his troubles … he lives in a one-room house with his wife and three kids, they have on light bulb (for the kids to do homework) connected to their next-door neighbors house (who rip them off by demanding they pay half of the electric bill). Also their (cardboard-ish) roof caved in and broke their heat stove. Aha … I thought to myself … and invited him to stick around, help me build the rocket and learn how to build one for himself … to which the cold, roof-less gypsy replied “but what will my neighbors think of me when they see a metal barrel in my house?”

Anyways, this is a remarkable technology which has already improved our lives tremendously. So far, to learn about rocket stoves there was only one reliable resource: Rocket Mass Heaters book. In our Romanian posts on rocket stoves we’ve gotten lots of questions from people who want to also build one. My reply (though Andreea tries to be more generous) is that before anything else you must first read the book. Period. After that you should start playing, reading online, watching videos … and eventually you’ll have enough knowledge, confidence and materials to build one that works.

It’s hard not to run  into Erica and Ernie Wisner when looking into rocket stoves. If you haven’t yet then you’ve been doing something wrong … and now that you’ve read this you have no excuse. They have some detailed plans for sale (which we haven’t yet seen but promise to be very educative) and they teach extensively, mostly in the USA. I have often wanted to attend one of their workshops … but living in Romania makes it complicated and prohibitively expensive.

However there have recently been two Kickstarted documentary projects which made it possible for us to partake in Erica & Ernie’s gifts. We learned about the first one in it’s last hours and supported it. Now Paul Wheaton of Permies has embarked on another, larger scale production including 4 DVD’s which cover a lot of things that are not part of the first production. I am especially looking forward to learning about “fire science” and about using rocket technology for hot water (which is the first time such knowledge is being made available and we plan to implement in our new house). So we’ve happily supported this project too.

While the book offers important theoretical information there are many details and intricacies which you can only really learn about through direct experience. I’ve been able to pick up many tips and insights while watching videos that are already freely available online (most of which, I believe, are thank to Paul Wheaton himself). So I’m looking for tons more insight from these two production projects.

We’ve invested ~ $170 dollars in these two ventures. It’s a substantial sum of money (for us, though it goes without saying, much cheaper then even the cost of a workshop, let alone flying to the USA to attend one) that we were soooo happy to give. We’ve already gotten so much knowledge from what Paul and Erica & Ernie have made available freely … making this a no-brainer investment, one that made an excellent return before we even made it. So we are grateful for this opportunity to support this work (hopefully making it possible for many others to learn about it), to enjoy its fruits and to say thank you … and this time we learned about in time to write this post and let others know about it … that goes out especially to all the Romanians who have asked … this is (for now) as good an answer as you could wish for 🙂

Fixing Our First Rocket Stove

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 …