Johannes Schwarz

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since Mar 28, 2016
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Recent posts by Johannes Schwarz

Winter might come back this week, most likely killing my fruit harvest (everything is in bloom right now). But it gives me one last chance to use my vortex stove (rocket stove relative) to heat and cook (I posted a vid of the build here before
Over winter I've been getting fat on bread and mini pizzas by putting in some fire bricks at the end of the burn cycle (with coals still glowing). When the fire bricks have absorbed sufficient heat and the walls still give me 350-400 °C, I put in the mini pizzas for 2 minutes and waith 90 minutes for the temp to be right for bread. The chamber is rather small (~ 30 cm x 30cm x 35 cm / 12 x 12 x 14 inches) and hotter towards the back end, so I have to watch things don't burn and maybe turn the stuff around for even cooking.

With summer coming eventually my attention is turning to the outdoors stove I have (I have no electric oven in the house which I could use during summer. And heating up the house is not a desired option)
It is a pizza oven built by the previous owner but I think it has some design flaws (the top part is a regular pizza oven going in deep (1 m / 3 feet; the bottom part is not connected and can be used for bbq, which I don't do much, because I don't eat much meat). It produces more smoke than heat (bad air flow design) and like any full blown pizza oven it takes a ton of wood. Once visiting friends used a quadcopter to supply air through a metal pipe which got things rolling and temps to perfect height. 8 hours later I could have still boiled water. But overall I'm not happy with it. I'm a hermit most of the time. Burning a ton of wood for a pizza and a loaf of sourdough bread for a single person is not economical.

This is why I'm thinking of modifying the existing structure and build a rocket into it looking something like this:

The goal is to reduce the amount of wood burnt (and preferably use stick wood I can collect in my woods), by:
1) making the burn more efficient -> rocket;
2) decreasing the size of the cooking chamber and the mass to be heated to fit my specific hermit (single household) needs.  Essentially I will build a cooking chamber inside the large old cooking dome.
3) Put the (thicker) bottom of the cooking chamber above the heat riser to get bottom heat.
4) let the hot air flow pass through the cooking chamber giving the top and sides some heat. Since the chamber is relatively small it should heat up like the cook plate of my vortex (which reaches 400°C) as air passes out the front opening of the smaller chamber into the bigger chamber (bell) from where it will go the usual route towards the chimney above the oven door.

I know there are some pizza/baking oven threads here and I looked at them. Obtaining real pizza heat is a problem from some in their design. I think I should be able to achieve high temps in the small  cooking chamber. By reducing mass I might have a problem maintaining longer lower heat for bread. I could get around that by going flatbread for the summer months if that is the case.

Any thoughts?

Hi Satamax, neighbor from the the other side of the border, you seem to be active on the pizza oven front. How's it going?
1 year ago
Glenn that is one cool looking stove! Bread from the heart of the dragon.
1 year ago
Hi Thekla,

the stone foundation of the stove is made with regular cement
the parts of the burn chamber are made with a special (and expensive) cast material (up to 2400 °F)
the fire bricks are layered with fire cement.
I guess half the video is mixing stuff
2 years ago
Hi Len,

Over here we use "Kachelofen" improperly sometimes for what strictly speaking should be referred to as "Grundofen" which may or may not have tiles [=Kacheln]. In fact where I come from (or the era I come from) most of these types of stoves have few tiles, and if so, they have them mainly for decoration and that is why they kept the name "Kachelofen", I guess. What makes them special is not the shell but a heavy chamotte core. That is why I put "Grundofen" in brackets (which technically does not refer to the heavy core but the fact, that you light the fire "on the ground" instead of a iron grill atop an ash tray. A Grundofen does not have an ash tray). Aside from Kachelofen types that are Grundöfen, there are also types of Kachelofen that are all tiles (and thus certainly properly called so). But they are completely unlike a Grundofen, since they are relatively light and don't necessarily have to be built on the spot but are in principle (and some in fact) moveable. They are a type of wood burning stove with a metal fire box and no heavy thermal mass (thus no significant heat storage). They use the tiles for optics and heat transfer (instead of a metal design for example). The way you fire these two types of "Kachelofen" is very different. In a Grundofen you put all the wood, kindle the fire, and when all has burnt down (no more flames, just glowing coals) you have to close the door and lock it shut (no more air intake). You must not open it again or add wood. Depending on its weight it will take  hours to get warm on the outside. But then it gives off warmth for 12 to 24 hours depending how heavy the stove is built (well, technically, you must not open the door as long as there is the potential for wood gases mixing with oxygen over glowing once all is ashes, you would be fine). The second type of Kachelofen you heat like a regular wood stove. You keep the fire going and add wood.
A Kachelofen of the Grundofen variety with its layout of "heat channels" will need to be carefully planned (and usually built) by a professional to work. It can easily cost from 4.000 Euro to 10.000 Euro depending on it's desired heat storage capacity. But it belongs to the most efficient wood burning systems out there and is the "heart" of any house that has one. The untranslatable Austrian term "Gemütlichkeit" really is not imaginable without it in the winter season
The other type however may be bought pre-fabricated in a store if it is small and portable or assembled at home (by someone knowledgeable still).

It was mainly the price tag and the practical impossibility of getting a professional Grundofen builder to my mountain hut that made me explore alternatives and landing me here Now I'm happy with my hybrid combining different concepts. But I also did get a CO alarm, just in case there is an issue with the chimney airflow and I have gas coming the other way. I am after all not a professional. And what I was allowed to build here in Italy, would have required expensive certification by a chimney sweep in Austria. Stricter laws over there.
2 years ago
Hello everyone and thanks for the kind words.

I posted the video a couple of weeks ago, so I was surprised to see a big spike in the vimeo view count this morning. I guess, this means it got cold wherever you guys are. Heating season is on

you are right. Looking at my exhaust temps, I could have increased the thermal mass and made the top section (which is one large bell) larger. On the other hand, my place is not very big and I will see this winter how I fare with the dimensions I chose. One of the reasons I did not go bigger, aside from over heating the place, was that I was not sure how much I could alter the plans I had, without it stopping to work (chimney draft and all). It was the first stove I ever built, so I mostly tried to stick to the things I knew were working in the original design.
As for the classification of the stove, this particular design shares properties with different types of stoves and I'm no expert. I put it here under wood burning stoves mostly because it burns wood and the category seemed to me more general, which might just be because I'm not a native speaker. But I see no problem with flame wars. They would appear fitting when it comes to stoves and "things heating up" is a good thing for the approaching cold season Here is how I would describe Trev's vortex design, my stove is based on:
The way the burn chamber is constructed there is some horizontal rocket action going on upping the temps.
The way the thermal mass  is constructed it is a masonry stove.
The way it looks on the burn chamber side with the glass door is like a wood stove.
The way it can be used is like a kitchen wood stove with its cook top and oven.
The way it behaves is like the Kachelofen (Grundofen  - ask google for pics, I did not get a proper translation. It is typical for Austria and southern Germany) I grew up with. It stores and radiates heat for 10-12 hours.   

C Jones,
well, if you live in a really nice place I could consider building one for you. Then again, if the place had palm trees, you would not need a stove But if you are half serious about the idea, talk to Trev over at donkey32. He has actually built several for other people and he is the real pro.
As for efficiency, I will know more after the winter. I made some temp measurements on my third burn with one of these laser thermometers, but it is off ebay and I'm sure it is not industry quality and might be off a little. Better and more meaningful stats I can provide after the winter. Here is what I noted down and recall:
Since I still lack a scale, I don't know how much wood I used in that burn but I would estimate it was:
20 pounds of really dry mixed wood (beech, birch, chestnut, stuff).
Half of the wood to start the fire. Half of the wood added after about an hour
burn time: about 2.5 hours
heat in the burn chamber (pointing in the fire) reaching 1700 °F
insulated walls of the burn chamber reaching about 1200 °F
top cook plate reaches about 830°F (water does get boiling quickly)
glowing coals: about 4 hours in. Burn chamber walls radiate 850 °F inside. A little wait and you have perfect pizza temps.  2 hours later it is bread time.
exhaust pipe temps right out the stove peak at 300°F (i also built a short cut for a better draft, which I use when kindling the fire) and go down to about 170°F. When the fire is out, I flip a lever to put the damper of the pipe to use.
surface of thermal mass reaching 180°F in some parts on top. 150°F in others. Since the surface is not smooth (like metal or tiles) but rough, it can be touched and leaned against, though during the hottest time of the cycle I would not press myself against it for too long
after 10 hours: thermal mass temp is at 110°F
after 12 hours: thermal mass temp is at 90°F
after 18 hours: burn chamber walls (inside) still radiate in the 90s. Thermal mass section has room temp (71°F)

I plan to experiment with a heat sink around the stove pipe to reduce heat loss through the exhaust.
One further modification I plan is a tube for secondary air in the top half of the burn chamber. The burn is clean as it is, but oxygen is always fun to add and should give even better efficiency burning all gasses. At least I think it will.
I don't think I need any of these improvements to make my place warmer (though we will see in winter - I'm in the alps at 4000 ft), but if these tweaks make the stove more efficient, they will save some wood.


2 years ago
Hi Antone,

how's the western side doing? Did you finish your huge RMH?

If you mean the sequence towards the beginning (and the very last frames), this is the SE view from my house down the Val d'Angrogna towards the Po plain with the Rocca Cavour in the center.

Cheers from a little further south-east,
2 years ago
I would like to thank everyone on these forums for sharing and helping others.
After browsing through the RMH section I ended up with something called a Vortex Stove (More about the thing here: which has some horizontal Rocket Action going on, but I guess is a wood stove and thus belongs here.

To give back to this community I wanted to share a timelapse-ish video of the build, to encourage people to experiment. If I, a priest and theologian in training, can do this, most of you will do much better still. So without much further ado, I present you with the "Hermit's Hot Hog"

2 years ago
Ok, it took me a while but I have realized my build using a variation of the RMH called Vortex Stove (More about the thing here:
Here is a short clip about the process:

Thanks for everyone in this Forum to share with and inspire others. It was a great help for me, so again, Thank you!

Piemont Joe
2 years ago
Thanks Erica for your suggestions. Most of the day I was fascinated by the vortex stove. That might be an option. The other thing I had been thinking about is the following:

I told Peter about this design over at the Donkey - judgement pending. But I'm sure some of you have suggestions as well.

Please no-one laugh. I'm no artist with my pointing tool and probably don't know what I'm talking about, but here is my "design" based on what I've read (batch + bell + a little dragon + a little walker). Input is welcome and advice on measurements much appreciated.
If disillusionment is the only way to cure me, then please do not spare me and beat the nonsense out of me.

The proposed name? "Hermit's Hot Hog!"

From what I understand the exhaust pipe diameter is (since I'm not free to chose it in my case) an important factor when calculating the rest of the contraption. Well, I have a standard 12 cm (about 4,7 inch) pipe inlet into the chimney (which is made from brick, not insolated and about 5 meters (16 feet) to the top from where the stove pipe meets it. Total length from the ground up is about 6.5 meters and this heater would be the only thing plugged into it.

*What do you think of my "flatbread oven" (a little central asia in 'da house'). This is what a chamotte pipe would look like:

They come in various sizes - even 12 cm for a heat riser (to be insulated on the outside obviously). Since chamotte retains heat the updraft would help towards the end of the fire, I imagine.

About the dimensions I'm open to suggestions. As I said I have two rooms on top of each other with 13 m² each (about 140 sf each) and a volume of a little over 2000 cubic feet (about 60 m³)
All sides feature 60 cm (2 feet) stone walls currently without insulation. I would put insulation on the inside (wood + wood fibre) if I have to but if the rocket stove output would keep things temperate then I could avoid insulation because it would come at the price of condensation between the stone walls and the wood (which is always better to avoid obviously, rather than trying to dry it out with my solar air collector in the course of a season).

What if I had too much heat? I would channel it to my "out house/bathroom" which is build on one outside wall and otherwise has only minimal spot heating when I take a shower (you gotta be tough).

I'm excited about this, but do not spare my feelings.

2 years ago

Thanks everyone for making this site a great resource.

I just recently discovered the RMS and RMH system and love it. I'm waiting for the books to ship and delve into the matter, but I do have a few basic questions, that people might be able to answer from their own experience.

The biggest challenge over here in good ol' Europe (despite the Irish now having the first CE certified RMS in production: the EirEco) is the regulatory jungle and the fact that in some areas you will need the local chimney sweep to authorize the system. Now most of them e.g. in Germany - a cursory reading in a "Schornsteinfeger" forum suggests - are not familiar with the concept and would not give their "blessing" to an open fire place (which are forbidden nowadays - regardless of how the RMS works with the draft). They want to be on the safe side and they are naturally being very conservative, since a failure of a system they permitted might fall back on them with all ugly consequences.
So if I wanted to build a RMS chances are that I need to do some convincing. Consequently I'm trying to eliminate the main objections, I have read in their forums. Maybe you have some ideas as well.

Some infos about my desired installation location (a clean dry rustico [a hut] in the italian alps):
Concrete/stone floor, two small rooms on top of each other (connected with stairs): together they measure about 2000 cubic feet. The walls are - currently without insulation - are 2 feet wide stone walls.
Only other heat source when the sun is shining: solar air collector facing south for ventilation and some nice bonus heat.

-Img does not work -

What I like about it:
It has a smaller metal radiator area compared to ones using a barrel (only the top of the tower for cooking). My rooms are so small that I fear that a barrel would make them too hot very quickly. I prefer the added mass around the secondary combustion area which could give off the heat slower. I have a lot of Grog laying around that could be incorporated as thermal mass.
Not using a barrel would also help with the first objection of a chimney sweep I read. The whole thing would look and feel more lake a masonry heater. With the barrel he might argue that over time (say in 10 years) the extreme heat would damage the material and waste it away. I could contradict him, but barely convince him, I fear.

Here another mod I think would increase my chances to get the "ok" from the chimney sweep: Outside air supply. With it, I could fill the hopper (which I would make a little taller as some folks have already done) and once the stove is fireing away I could close it with a glas stove stove door. That way it would prevent any harmful gas flowing back in the rarest and most unfortunate of circustances - which is the biggest concern of some chimney sweeps I read on the topic that are not familiar with the trusted working of a RMS: "but weather conditions might....". Naturally I can use a metal pipe for the outside air transport to avoid the potential fire hazard that was described in a fictitious case used in a thread about outside air in these forums.

What do people here think out this?
Anyone here with a barrel-less design?
What dimensions (mass) would people recommend for my application? Anyone have experience with small rooms? Using pipes for leading the gas inside the thermal mass to the unisolated stone chimney I'm stuck with 4.7 inch diametre (12 cm) which is what the exhaust pipe has.
And: Ci sono Italiani qui con una stufa a razzo?

Any input welcome.

2 years ago