Rocket Stove article
Year-Round Building Blocks:
Most Rocket Stoves are built by tinkerers, homeowners, and communities, rather than professional builders. This can be a daunting project, especially for a first-time masonry builder. If you come to us looking for a rocket stove, we want you to fully understand what you're getting into - from the mud and grit all the way up to the finished product.
Photo albums from previous projects:
Rocket stove builders frequently post to the forums at www.permies.com:
and others create their own update pages on Facebook or Flickr.
Here are a sampling of owner/ builder reflections:
Report from Andy of Fox Circle Farm:
So here are my rocket stove thoughts. As I look back on the building of that stove, I realize how much I learned in the process. Once again thank you both very much. The stove totally changed the vibe of that room and made it a livable space for the winter.
Rocket Stove Reflections from Fox Circle Farm From Andy
We built the stove in December of 07, it kept 5 people very happy through the winter and spring until the redwood valley warmed and the coolness of the house was a welcome feeling from the heat of the sun.
Though we only got to use our rocket stove for probably 6 months, I believe at least a 100 people who had never heard of a rocket stove became exposed to them because of this stove. Over the course of the building of the stove we had at least 25 different people work on completing the stove. In the end when we found out that the property was getting sold and we would have to leave, we put a hurried finish plaster on the stove to "dress it up" for a community building/networking event we hosted at Fox Circle Farm. It was bitter sweet, to finally dress the stove up and see the smoothness of all the curves come together, the whole bench and stove gelled together, and at the same time we knew that the stove was likely going to be torn out by the new owner. The property was bought by the wealthy neighbor and the word on the street when we left was that the whole house would be gutted and completely re-modeled. A practice in non-attachment! I will take my stove building lessons with me! I cannot wait until I live somewhere where I can build another one.
After going through the first season of living with my rocket stove, here are some of my observations in no particular order.
If we were to stay at Fox Circle Farm longer I would have lengthened the chimney pipe. On the stove we put the chimney out the roof as a safety, prevent smoke back feature, make the stove look like something that burns wood, and the chimney ended right at roof level. This was below the crest of the roof on the creek side of the house. Through most of the winter, cool air drains down the hillside, over the roof of the house and then into the creek corridor below. Which meant that when the stove was burning the stove exhaust was wisped into about head height on the walkway to the main house. This was not too big of a deal for me when the stove was reaching full combustion, but our wood was often wet, and combustion not complete, so people often had to walk through smoke to get to the main house. However, because of the placement of our chimney I did get plenty of entertainment watching out the window at the smoke showing me the air flow patterns around the house. It taught me a lot how air moves like a fluid.
Late in the winter we started getting smoke back problems. I would clean out the fire box real good, make sure we were using good dry wood chopped small, but still we would get smoke back. This was getting to be a pain in the butt and was discouraging people from using the stove because they did not want to deal with it. So I unscrewed the bunghole to the drum heat exchanger and looked in there with a flash light. I focused my attention on where the flue started and interfaced with the outside of the burn tunnel. It looked a little clogged with ash. So I jammed the hose of the shop vac in there at an awkward angle and tried to suck the whole thing out. Afterwards it worked normal again. If we were to stay there longer I would have removed the barrel, and made this interface a little larger. Then I would have stuck the bung hole of the barrel directly over that spot so it was easy to vacuum out.
When we built the stove I did not have a barrel to use as a feed barrel so we did not put one on. The idea was that I could do it later. I never put one on. Once we had a smoldering piece of wood fall out of the feed tube when someone was not tending the fire proper. We burned a hole in the carpet. Later in the season when we were starting to get smoke back problems, not having a feed barrel also made it challenging to constrict the opening of the feed tube enough to suck the smoke down. In the future I would put a feed barrel on without hesitation, especially in a place where the stove will have many different users.
When it was cold out, and the stove had been going all day, nothing felt better than lying on that bench at the end of the day. Even though the bench was rough cob with a blanket over it all of the winter, nobody cared, it was warm earth and it felt good! The bench was a favorite location for watching movies from.
Rocket stoves are aphrodisiacs watch out… I can't imagine having a rocket stove for a bed…
It was really fun to watch the chimney as a diagnostic of how complete our combustion was. When I saw smoke frequently, I chopped the wood smaller, or made sure to have a mix of small and large pieces.
It was challenging to get a smooth plaster job using volunteer semi-skilled labor. In the future, I would pick one or two people to work with and if they were not that experienced, at least I could coach them easier than 5 or more people.
The firewood drying area beside the burn tunnel was key in the winter.
Reflections by Erica:
I started my Rocket Stove career helping Ernie to do a benefit workshop a few months after being hurt. Our friends at Try-On Life Community Farm hosted the project, to install a rocket stove in their outdoor kitchen. We created a modified version of the Cob Cottage Pyromania workshops, based on my science education background, Ernie’s hands-on masonry and fluid dynamics expertise, and the props and space available. I also drew the posters, and directed people whenever possible so Ernie could put his leg up.
The Tryon Farm rocket stove worked pretty much as planned. This bench is designed for an outdoor space where people will be heated directly by sitting on it, or by standing very close to the barrel, during celebrations and cooking workshops. Several toddlers and small children live there full time, and many children visit every month, so we chose the barrel size and configuration to make it difficult for anyone to burn themselves even by accident. Ernie sweated over the details in a pain- and painkiller-induced haze, while I stood by to follow directions. Details of throat configuration, barrel size and orientation, and piping and firebox sizes, all escaped me as too subtle for my contemporary understahding of the dynamics. My one contribution was to suggest putting the final length of the exhaust pipe vertically up next to the barrel, so that visitors would be likely to connect the “smoke” or steam coming out of it with their normal expectations from a woodstove, and anticipate that the barrel would be hot before putting their gear on it.
Whatever Ernie did, it worked. As planned, the barrel gets just “barely” warm, while the entire bench heats appreciably within a short amount of time. The handy and cheerful team at TLC Farm decided to plaster around the barrel anyway, though they left “eyes” and “nostrils” exposed where one can touch the metal if desired. We visited it again almost exactly two years later, in fall 2008. It had been given a lovely two-tone finish-plaster coating in the shape of a dragon, with the wood-fuel intake being the “mouth.” A new and improved roof is being built over the outdoor kitchen, with cedar shake on a spiraling roundwood frame, and the whole effect is quite charming.
Toby Hemenway’s stove, arguably our highest-profile project, was a different story. Toby had attended the TLC Farm workshop, and liked the rocket stoves very much. Toby and wife Kielle had wanted a heated bench in their garden, and decided to add a shed-sized sauna to use the radiant heat from the rocket stove barrel. Ernie was approached to lead the workshop, scheduled during VBC2007, but much of the design had already been done. The hosts wanted a rocket stove with the feed tube outdoors, the barrel inside the sauna/shed, and the exhaust flowing through an outdoor bench attached to the same wall. (The “firebox-outside” theory is a popular, but nightmarish, configuration. The longer burn tunnel (to go under the wall) requires a heat riser substantially longer in turn, and even so, any flammable materials in the wall are likely to be dangerously close to the feed tube, the barrel, or both.)
As I was working part-time and still a bit inexperienced in the building trade, Alexis Jaquin was added to the team to keep the walls and plaster going steady. She did a lovely job, and offered a contrasting teaching style that broadened our range of audience.
Toby is a beloved teacher and author, and has become somewhat famous among the natural-building community for his work in permaculture garden design. His small yard was full to bursting with a series of garden, seed, greywater, and healing arts workshops. Our rocket stove workshop squeezed in about 60 people (in a 1/4 acre yard) and we clocked more than 600 visitors over the course of a single day. This went on for ten days.
In all the hustle and bustle, we went to work with assorted pipes of various sizes. We tried adding an air intake since the burn tunnel was buried underground. It was made of a bend of gutter piping. Over the course of the week it got filled in turn with dirt, cob, straw, more dirt, and rocks.
The stove fired sluggish on the first try, but did work. Loads of ceramic clay were donated, and high-grade slip made the masonry and straw-sculpting easy.
I dropped Ernie off one morning to start prepping the walls for building. He took one look at the chickenwire they’d strung to support a plaster “skin,” and declared it unworkably loose. A couple of competent handymen had installed it, but not knowing the requirements of old-fashioned earthen plaster, they hadn’t bothered to tighten it as much as Ernie would have done.
With so many people in a small space, I’d show three people how to work cob, go check on the other four people stomping out a fresh batch, and come back to find my original three people having disappeared and whole new bunch attempting to carry on what they thought they saw the first three doing. During sculpting, someone stepped on the wet bench and crushed the pipes. By the end of the week, the stove was still firing sluggishly – in fact, when you removed the outside “smokestack,” the “smoke” drifted downward like dry-ice fog. Heavy fog, slow draft, and a tendency to “choke up” or smoke back. It took an additional three months of part-time work to finish the stove, including tearing out the bench and straightening the pipes, and we ended up adding another foot to the heat riser. Still burns weird.
It was about six months later that we realized, although the firebox and exhaust were designed as a 7- to 8-inch system, the heat riser’s internal diameter was in fact only 6”. Wonder if that could have anything to do with it?
We taught a workshop at the Fox Circle Farm field station in California, and the students there built a fairly standard 8" stove. Andy's report on the process is above.
Then… another whooper. TrackersNW arranged a workshop in a rented building, shaped something like an egg – or, in retrospect, an airplane wing. The basement space needed extra warmth, but the renters, owner, neighbors, and workshop organizers were not all on the same page about the idea.
Ernie and I would have preferred to place the stove in the point of the curve, for even heating of the entire space – but the client wanted it in a less central location to increase the usable footprint of the open space. One of the instructors set about getting a permit for the stove, but ran up against uncertainties and deadlines and, essentially, decided to let the workshop happen first and the permit after.
After cobbing everything together, we test-fired the stove and discovered … the entire building drafts toward the south, effectively turning the basement into a giant vacuum chamber. With enough doors open, and the fans turned OFF, and a windbreak in front of the exhaust, the stove (sometimes) drafts. With even one south-side fan ON, or the door closed, or the wrong breeze, the stove serves as an extra vent to draw fresh, smoke-enhanced air IN to the building.
And we also discovered…
- That the neighbors have a longstanding grudge against the ugly rental building and its "weird" renters, and make a habit of calling various city departments to complain about any annoyance.
- That the gravel parking lot alongside the building is in fact a public parking lot, hotly contested territory for neighborhood businesses. People stomping mud on tarps in said parking lot constitute an annoyance and possibly a code violation.
- That smoke coming out of a hole in the wall DEFINITELY constitutes an annoyance, cause for alarm, and a probable code violation.
- That the City of Portland gives you 30 days once they discover your non-permitted stove, to pass inspection and make any required changes to get your official permit, or to remove the stove.
We removed the stove, leaving the bench in place. But with the ownership and wind conditions, it seemed like a case of "pick your battles." It was a pretty good place to run a workshop, but not a good place to build a stove.
Now we embark on another stove, this one in the living room of our little rental house. Our landlady hopes one day to transform this once-country property, now within Portland's city limits, into a center for ecological learning. She gracefully obtained a permit, describing our stove as a “wood-fired Rocket Stove masonry heater,” with a requirement for inspection upon completion or within at most 180 days. Cost about $40.
We obtained pipe of consistent size, 6” diameter, mostly recycled with a few new joints.
We had on hand three sizes of brick to choose from.
The landlady graciously offered to pay for some of the more expensive materials, such as the double- and triple-walled pipe required for conventional woodstoves’ through-wall connections.
We live in a city that has a “ReBuilding Center” that sells salvaged lumber, metal, tile, and other sundries for very low prices.
We had only one workshop assistant for the first two days of work, so Ernie and I were able to personally do or oversee each part of the initial layout and masonry. As a result, this stove has more parallel lines, and more solid joints, than any we have worked on so far.
I wonder what will go wrong?
Two weeks later, we are enjoying a cold snap. I say "enjoying" because the stove is really shining.
We are finished with the cob core, and waiting on the right day to do the plaster scratch coat and color-samples for the finish plaster. We plan to tile the front and put the stove vent thru the roof before calling for final inspection.
We finished the plaster, and had our first inspection. And then a second inspection. See Rocket Mass Heater Permitting for more details and links about what it's like to try to meet building code and get official approval for this stove.
So far, it's still in limbo - but we love it, and so do our guests. Check out pictures of the building process at: http://picasaweb.google.com/eawisner.