The Cabin Stove – A Small Masonry Heater at Aprovecho Research Center

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Important note: I have preserved this post as-is for archival purposes. On-going development of the Cabin Stove is documented at The Cabin Stove Page.

A good part of the month of August has been dedicated to the research, development and construction of a small multi-functional masonry heater I have been calling “The Cabin Stove”. Eva and I have both been working as instructors in the first year of the Sustainable Shelter Workshop Series at Aprovecho Research Center in Cottage Grove, OR. The building that is the focal point for this course has been designed to be just slightly smaller than the legal requirements for permitting so that it can at the same time be a teaching tool as well as a laboratory for a basic building system that a group of associated natural builders in the Pacific Northwest considers to be a sound and ecological way of making a home.

The challenge of the design of the Cabin Stove was to come up with something that was very compact but also still resembled and functioned like a masonry heater. The design criteria included heating the small space, an efficient and clean fire, utility for cooking, heating water, combining some quick/immediate-releaseheat with slower retained radiated heat, relative ease of construction, not too expensive, aesthetically pleasing, and being as compact in size as possible. A very interesting process to try to combine all of these together.

Our test firings of the prototype in our shop were very promising. The fire burned well and had no problem making its way through the longer pathway, even notably when the door was open with the beautiful cast fire screen reducing the overall air intake to a moderate amount. I think the design meets most of the criteria listed above well with the exception possibly of cooking utility since this was compromised to accommodate other features.

For the initiated, it is basically a very compact J-loop contraflow with a bi-pass that runs directly to the flu and allows it to function even as an open fireplace. Rather than insulating the top of the heater as is done often in masonry heater construction, there is a 1/4″ steel plate placed on top that serves as a cooktop and source of immediate heat. I am optimistic that the proportion of immediate and retained heat will be a good one for our bio-region where temperatures can fluctuate greatly during the day and from one day to the next. We are within but on the outer limits of the kind of climate that masonry heaters were designed for which explains the need for continued development and innovation.

I did notice in firing the prototype that the big steel plate I had placed on it arced noticeably when hot so I welded a 3/16″ frame onto the Cabin Stove we built at Aprovecho though I am quite sure that the heat will play its funny games and have its own way with the final shape of the steel plate. Cast iron is almost certainly the way to go for the top although I do not know of a source of affordable custom sizes.

Although the heater at Aprovecho was designed to be a double-skinned heater with a compressed earth block and local stone veneer, I am very excited that we will first test the heater with a single skin. A neighbor has offered to lend his carbon-monoxide and air-quality monitors to test whether there are any dangers that result from expansion cracks in the single skin. Given our climate in Oregon, the prospect of building responsive single skin heaters is a very interesting one. (Note: the variation in the firebrick is because we used firebrick out of an old heater that had been taken down. The students re-milled each brick to cut away the old mortar to return the brick close to original dimensions).

I have recently been very inspired by the Open Source design philosophy so I share the rest of these photos of process in that spirit! Stay tuned for more on this heater and other research and endeavors. Click to see any images enlarged.

You can see some other details of the building, including one of the timber frame’s posts; the faswall and stone stemwall; and strawclay insulation packed in between Larsen-truss style framing.


Custom-made heater hardware, made in our shop from scratch.

Details of Hot Water Serpentine. More on Plumbing for Thermosiphoned Hot Water Systems….

Make sure to read this more recent post on the Cabin Stove 2.0!

The light and surrounding forest were really exquisite when I took these shots of the veneer material. The compressed earth blocks were made by the students.

Find out more…..

Cob Masonry Heater at Cob Cottage Company

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cob masonry heater group

This is a very exciting and experimental masonry heater built by many hands through a workshop at the Cob Cottage Company in southwestern Oregon.  The challenge – that Ianto Evans is so consistently a champion of – was to build a masonry heater that was made of local materials and through local craftsmanship.  Flemming Abrahamsson, master mason and incredible human being, traveled from Denmark to guide us in the work based on his decades of experience as a heater builder in Europe.  The inside of the heater is based on a Swedish 5-run design.  It is a single-skinned heater which has a firebrick core and is faced with recycled brick set in a clay-based mortar from clay dug on site and cob.  The hardware for the heater was fabricated by Max – his first arched glass door!
The plaster and paint were made and applied during a class taught by Eva Edleson and Jo Forsyth during the Complete Cob Course.

Jon Santiago, one of the participants in the course, documented the build wonderfully in this Facebook album.  For those interested in how it was built, it is worth zooming in on each photo.

Join our mailing list for updates about it how it fires and performance through the winter.

Further reading…..

New heaters in the world – a summer update!

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This summer has been an exciting time to deepen our craft in masonry heater building.

Here, Jerry Frisch of Lopez Quarries and I are standing in front of a heater that I assisted him on in a new house on the Puget Sound in the state of Washington.? It is a basic Finnish contraflow design which includes a bake oven and a heated bench on two sides.? Other masons from the Masonry Heater Association also came to help out on the heater as the whole effort was part of a? fundraising effort to raise funds for the MHA in order to be able to do lab testing on stoves to prove empirically to the EPA how clean-burning and efficient masonry heaters are as they draft new regulations for wood-burning appliances due out in a year or two.? A more in depth story will follow…

And here is an interesting project that Kiko Denzer and I just completed:

This was an interesting project that involved modifying an existing solidly-built woodstove into a masonry encasing in order to extend its flue path and create mass that would absorb more completely the heat from the wood burned.? It has a “bi-pass” damper, which acts as a valve, and allows one to heat up the flue directly.? When this damper is closed, the gases then follow a different route: back down, through the bench, and then up to where it re-unites with the original flue.? There is another damper called a shut-off damper which is used when the fire has burned out completely to shut the flue system completely and hold in all the amassed heat.

Construction shot showing flue liners in bench:

This project also represents a breakthrough for us in being able to do computer-aided design to conceive of and plan a project.

This is simply an update….? we will post much more thorough posts about each project when the dust from the summer has settled!? ‘Till then!…..

CIDEP Rocket Mass Heater

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Rocket Stove @ CIDEP
Rocket Stove @ CIDEP
Rocket Stove from back @ CIDEP by John Santiago

What is a Rocket Mass Heater? A Rocket Mass Heater is a wood-fired device which is clean burning, affordable to build, uses local and recycled materials, and creates a wonderful kind of warmth for heating cottages and small homes. In a very unique way, the Rocket Mass Heater combines both the immediate heat offered by regular woodstoves with both the clean-burning and mass-accumulating features of masonry heaters.

As part of a phenomenal event called Bioconstruyendo held in February of 2010 in Patagonia, Argentina, Max led this very successful hands-on project of building a Rocket stove in a beautiful cabin framed from recycled barn timbers and in-filled with straw bale and adobe to create a very tight passive solar building. Considerations in the design included: having the firebox relatively near the door in order to be able to stack and dry the wood just inside the door, creating a daybed that would accomodate a twin sized mattress to act as a day-bed in the solar windows and as a sleep-over pad!

The first photo clearly shows the combination of the metal surface of a polished 55-gallon drum which radiates immediate heat to the space along with the “massive” day-bed made out of adobe bricks which stores the heat that the flue gases give off as they travel down and back the full length of channels inside the day-bed before exiting out the side wall.? The second photo shows after final plastering and the third photo shows where you load the wood into the unique down-draft combustion chamber of the Rocket Stove.

If you’re interested in learning about how to build your own rocket stove, Rocket Mass Heaters is the definitive guide and a good place to start. We look forward to developing more information on our site about rocket stove building so stay tuned.? It is quite a new technology so it is an extremely exciting area for research and investigation. I have been doing some interesting experiments in trying to refine the rocket stove by combining it with elements of masonry heater construction. Take a look at these two projects built as workshops at Wildacres documented on the MHA website:

Links to come:

-Process of building this Rocket Stove.

Read More….

Masonry Heater in the Rio Azul

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This is the masonry heater that we built in the central community building of the Rio Azul community outside of El Bolson, Patagonia, Argentina in March of 2010. This heater can act as an open fireplace to provide the magic of fire and cut the chill in the late Spring or early Fall… but it really shines through the cold months when you close the first damper and send all the hot gases through a full round-trip in the day bed before they leave through the chimney. When the fire has gone out, you close the second damper to keep all the accumulated heat in the stone and adobe inside the building which emanates until the next fire you make the following day. There are pipes in the firebox that heat water in a hot water tank which is above the heater.

Most of the heater was built in our Naturally Building for Fire workshop that I led and then Eva and I did the finishing work afterward. Here you can see a little more of the context in which the heater was built. You can see the community kitchen in the background. The heater helps to form the living room / hang-out area. There is a sleeping loft in between. The building currently acts as a barn as well which is why garlic and herbs are hanging and bins of seeds are all around.

This heater also represents a breakthrough for us in making our own hardware. My old metalsmithing teacher let me build the firebox door, dampers and cleanouts in his shop.

More about masonry heaters….

Wood-Fired Cookstove in Bali, Indonesia

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In May of 2009, I traveled back to the island of Bali, in the Indonesian archipelago, where I spent much time as a young boy.  The island, its people and its culture continually inspire me… the degree to which they are immersed in and work together with their natural environment, their exuberantly-expressed spirituality and their tacit commitment to craft as a way of life.  During my time there, I built this wood-fired cookstove in which I combined the local architectural elements of the wood-fired cook stove in traditional (black!) kitchens with what I have learned about sealing the smoke into a pathway and combustion efficiency.

More photos and description of the research and construction process for this stove….

Rumford Fireplaces at the Cob Cottage Company

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During my stint as a staff member at the Cob Cottage Company, I was responsible for building three Rumford fireplaces.  Within open fireplace design, the Rumford fireplace offers the greatest efficiency in terms of  how much heat actually radiates into the room.  The Rumford design is characterized by a shallow firebox and a tall and open fire back which throws the heat into the room rather than straight up the chimney.

These Rumford fireplaces are almost entirely built with cob, a sculptable combination of clay, sand and straw.  The Cob Cottage Company, amongst other things, is a laboratory for simplicity…  so only the hearth and a couple of courses on the inside walls of the fireplace are made out of fired brick.  The rest, including the throat, smoke shelf and chimney transition are all sculpted in the same way that one would sculpt a large ceramic vessel.

The Ridge House Rumford:


The new dining room Rumford (not yet plastered):


The Rumford in the Castle: