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Summer Kitchen Renovation Part15: The Stove

From the beginning of this project, Iulia and I have had differences of opinion about a stove. You can say that the stove and these differences of opinion it represents is at the heart of this project. Because of those differences of opinion, the stove is late to the party. As a result, its placing and design were constricted by earlier choices.

The stove was NOT really a priority right now. Its chimney was. I wanted to complete the roof. The decking and water proofing layer were already in place. The chimney is a roof penetration and requires a hole! I preferred to make the hole before before putting on the shingles and then having to cut into them. And the chimney is deeply related to the stove. So … stove!

This stove is a departure from the rocket stoves I’ve been building since the beginning of my journey here at Bhudeva. The main driver for this change is that rocket stoves require attention. In our winter a rocket stove requires numerous feedings in order to keep a space comfortable for a day. 2-3 feedings are required on mild winter days, 4-5 on cold days. This implies a relationship with the stove. Iulia wanted out of this relationship.

One alternative was a batch rocket. I’ve been following batch rockets for a few years and have NOT been inclined to experiment with them. They seem to elevate the level of complexity of construction compared to a “regular rocket” … and I was not inclined to take this on.

I also encountered this article comparing rocket stoves to masonry heaters. It captured my attention but I did not explore beyond an initial reading because I did not have any plans to build a stove. As the summer kitchen renovation morphed from a conversation to a reality I started looking into it. The article led me to this “Russian Rocket” design and I’d casually spent time with it trying to understand its design. However, because of the above mentioned “differences of opinion,” I did not dig too deep … because it was not clear that I was going to design and build a stove.

When, late in the process, it became clear that I was going to build a stove, I studied it in depth. My experiences with rockets helped … but there was some new stuff I had to learn. After careful study of the stove in the article, I felt confident enough to take this effort on.

This stove, if all goes well:

  1. Is fed a large batch of wood that burns all at once.
  2. If designed and built well it should, like a rocket, burn cleanly so that little-to-no emissions remain.
  3. It uses a combination of channels through which the hot gasses can pass, and chambers in which the hot gasses can stay and stratify. The exists from the chambers are always at the bottom, so that only the cooler gasses can exit.
  4. As a result, most of the heat from the intense fire is stored in the large mass of the stove (all those bricks) and is slowly radiated into the space.
  5. It also has a “black oven.” This is like a pizza oven. The fire burns into the oven chamber, charging it with heat. Then, after the fire goes out, the oven chamber can be used for hours for cooking and baking (without a fire burning!).
  6. Unlike a rocket-mass-heater, it does NOT have an instant heating effect on the space. It provides a slow and constant radiated warmth. Depending on the thermal performance of the structure and Iulia’s climate preferences, it may be enough to feed this stove once a day.

The first thing to figure out was placement. After much deliberation and unfolding, we arrived at a location that we had not considered at all at the beginning. We were “blind” to this location because it required taking down one of the internal walls.

However, to do that, I first had to make space for all the soil that would come out of this wall so that, as with the rest of the cob, we could reuse it. So it was time for the old original door frame to finally come down:

Now, with that space available, I could take down the wall segment. In this picture half of it is down:

and here it isn’t:

… and its soil moved to where the door was, alongside all the remaining cob we are reusing:

By now I had a sense of scale of the stove-to-be. It was time to figure out its exact inner layout and footprint. Time to lay out some bricks and see what is possible:

… until I settled on to this core layout:

Now we had a foot-print and I could work on two tracks. I spent numerous evenings designing the ~30 internal layers of the stove so that we could determine roughly how many bricks (regular and fire-bricks) we would need … so Iulia could inquire about that.

Meanwhile I continued digging lower down to compensate for the height difference of the spaces the wall separated … and I made preparations for a concrete footing (sitting partially on the thin concrete floor that was unwittingly put in when I originally moved here):

… and then pouring the concrete:

Iulia found some recycled bricks … and we took delivery of 1000 pieces:

I decided to place insulation both underneath the stove and between it and the external wall behind it to reduce conductive heat loss.

We repaired (took down excess materials and filled gaps) where the old wall met the external wall … and then it was time to reconnect with brick-laying. Starting with a base layer:

… and first layers:

My past experiences cutting bricks with an angle grinder were successful but very unpleasant and messy … so much so that I avoided cutting bricks unless I really had to. This project was going to have more brick cutting than I ever did before. I practiced and got better at cutting with hand tools … and decided to (finally!) invest in a shop-vacuum … which made the work MUCH more accessible and MUCH less messy:

Meanwhile, we were searching for the metal parts that this stove requires … and most of them arrived just in time to allow the work to keep moving forward. The first was this metal grate that is embedded in the floor of the fire chamber. I cut it into three pieces, two of which went into the stove:

While waiting for the grate to arrive I continued to build up the outer skin:

… and then I could fit the grate pieces into the fire-chamber floor:

… and I could set the floor in mortar and build up the inner fire chamber:

Way back when we started this project we took apart a baking oven (that made this place in its original form a “summer kitchen”). The floor of that oven was made of large flat fire-bricks and though we could not get them out whole, we were able to salvage large parts. Now we had an opportunity to reuse them in capping the fire-chamber. We were able to assemble two layers to bridge the top of the fire-chamber made up mostly of recycled parts that were cut and fit together. Here they are dry-fit:

… and here they are in place with mortar:

We already had the fire-chamber door, but we were waiting for a ceramic band that goes around it in order to install it. The came late … but when it finally arrived it was possible to install the door:

… and to close up around it:

… now the top of the fire-chamber became the floor of the built-in bake oven … and, together with the outer skin going up around it, the oven chamber started to form:

… and finally … we could do a fitting of the bake-oven door:

… and then the oven needed a top … and we didn’t have any more nice large fire-brick slabs … so it was time for some bridging:

… and then with mortar:

… and the remaining spaces were filled out:

… and we got to work on the arch over the oven door … with an improvised attempt at carving shaping a brick fragment:

… and then closing that layer … and doing a mockup of the layout of the upper chamber … with a final location for the chimney (which is what I was really after this whole time!!!):

… and this felt like the beginning of the end … I could now count down 8, relatively simple, layers of bricks.

I started with another “floor plan” for the upper chamber and laid a 1st layer of bricks which established the structure:

… and then needed to prepare the cleanout door, it came as it set together with the fire door intended to be a door on the ash-pit, but we decided to repurpose it. I fastened it by drilling some holes and created some anchors using some good ol’fashion romanian “wire” work:

… and with that in place, we could continue moving up … until we could finally do a a first test-placement of the chimney:

… and then it was time to start capping the upper chamber:

… at this point we said goodbye to these spaces where warm air would be held, its warmth would transfer to the mass of the stove until it would be cool enough to drop to the bottom of the chamber where it would find the chimney exit.

… and at this point we got a little too excited and decided to do a test burn:

… it went partially well and partially less well … and I was a little concerned about the less well part … even though I had a feeling our experiment was premature and that the results were not indicative of the performance of the stove. We got very good flames:

… but also very good, but undesirable, smoke:

drafting = the way air and gasses flow through the stove is both simple and subtly complex! Eventually I realized that the biggest mistake was the absence of a high-enough chimney which directly affects the draft … which is critical in a masonry stove (compared to typical fire places or metal boxes with fires inside them). Indeed when I added another chimney segment things greatly improved … and when the entire chimney is installed … well … I’ll let you know how that goes 🙂

… and we moved on … completed the stove … this is me working in a tight spot to get the last bricks in:

and did a couple more test firings … still with mixed results … which worried me a bit … but only a bit because there was still some unfinished business which would affect the stove performance. Here you can see the completed stove already partially blackened from smoke from dirty burns (in an ideal clean burn there is no smoke at all since all the fuel burns either in the primary or secondary chamber):

With the chimney in place, we went up to see how it would connect to the upper part of the chimney. My working assumption was that we would just barely make the connection to the top section was wrong … we were too close. The chimney in the stove needed to move a bit. Fortunately, there was some room for “play” in its location and after a bit of dismantling (luckily much less then we imagined would be needed) we managed to shift the chimney and close the stove back up again:

We installed the bottom section of the chimney … and after some test iterations were able to install a frame extension to which the upper section would be attached.

The upper section is double-walled stainless steel with insulation. It starts with a base and a T-joint. We got it roughly located and held in place with clamps:

… and after some fiddling to get it vertically plumbed (so that the chimney would exit properly between two roof rafters … we got it installed … and Iulia is in this picture to give a sense of how big this thing is (we were surprised when all the parts were delivered … on a pallette! … they looked comfortably sized on the website!):

… and this is where we arrived today … and this is exactly where I wanted to be … ready to make a hole in the roof, install the rest of the chimney and integrate it properly into the finished roof surface.

The first bricks were laid on September 25th … so this adventure took a month!

note to self: the mortar (even taking into account the slightly too-thick mortar joints I made) … so much mortar. I counted almost 8 wheel barrows (~85 liter) of sand and 6 wheel barrows (~70 liters) of clay soil … which is … and I still find this hard to believe … just over a metric-cube (1100 liters) of material. When the materials are mixed together into a mortar they lose approximately 50% of their volume … but still … LOADS of mortar went into this.

and … to be continued 🙂

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