Vortex Stove

[Vortex]

If the chimney is about 7" square, I would be inclined to line it with 6" straight stainless, and fill around the outside of the pipe with vermiculite to insulate it. The lengths of straight 6" stainless could be lowered down the chimney one at a time and screwed together with self tapping screws as you go. I don't recommend the flexi-pipe, all those wrinkles create a huge resistance to gas flow.

Maintain the minimum Cross Sectional Area (CSA) through the whole stove, bigger is OK just don't go smaller. The CSA of your chimney can be bigger than that of the stove but not the other way around.

[jojohannes]

Thanks Trev. In two weeks I'll be back in Italy. I will post my progress here.

[jojohannes]

As my misery to find the right materials for the refractory cement in Italy continue (through an Edilizia, that actually will deliver it to my hut), I was thinking about the materials to mix the cement with
I was trying to find chamotte powder or refractory bricks powder.
Now, why would I not go for Vermiculite powder? I mean, if I should insulate the fire box, why not built that part from an isulation material, keep the flames hot and send all the heat to the fire brick heat storage "next door" (well, the other part of the stove)?

Good idea? Bad idea?

Update: Well, I realize it would be a bad idea for using the fire box for baking. So to keep my options open I will still go for a fireclay based castable. If the Italians do not come up with something, then I will use this material from an Austrian Manufacturer: www.rath-group.com/en/products/unshaped-products/rcc-castables/
It is 40 € for a 25kg bag (just add water)


Update 2: Horray. The Italians came through. The found something: Calde cast R 40 IT

[Vortex]

Looks like t should be OK: Maximum service temperature [°C]: 1370
www.unistara.com/catalog/base_deep_info.asp?F_DettCodice=1304&F_IdMarchio=01&Lang=en&S=VETR&F_TipoFiltro=S

[jojohannes]

Hi there,
back from the Italian mountains and internet limbo. This time I did floors, piping and bathroom stuff, so I haven't gotten around to the stove yet. I was waiting for the delivery of the Calde cast still. When I get back there in a few weeks it should have arrived and then I will put those molds to use. (I realize I still haven't posted any pics. I will do so after my next trip when I hopefully do not forget again to take some.

[jojohannes]

Alright,

sorry for the delay. I'm still not finished with "The Hermit's Hot Hog" based on the Vortex stove designs, but I'm using the hail storm outside, a quick break and a painfully slow internet connection to post at least some pics of my progress. I had a few fires now and can do a quick report. I also did some filming during most steps of the build and some timelapse footage that I will post here when I get around to edit it.

Ok. It all started with the molds, which I built according to the plans Trev shared. Thanks Trev! After pouring the castable, as suggested, I used the hammer-drill in reverse on some hard piece of wood to generate vibrations and the air came bubbling out. Worked nicely (though I did have mini bubbles up top that did not pop making the surface not perfectly flat. In the end my 150kg of castable was just a tiny bit to little, which meant that the parts would fit but the back side (middle) ended up 5mm thinner than required to create a flat outside. So I had to fill the space with some fire cement before I put the insulation (I used Promat Promasil plates) 
s


Next, I built a platform, the right side of which would also serve as a bench for my table. From the opening for a new door and making a hole for a stairwell I had broken bricks and stones left that served me well (and reduced my waste pile outside). I opted out of heating the "bench" mainly because I was not sure if it would work as desired (and I did not want to loose too much heat into the bottom of the construction.



Next I assembled the fire box, did some small fires outside to slowly get it to temperature. In this way I could also appreciate the vortex action happening in the top chamber through the hole on the side. When it was dry, I moved the parts inside and assembled them at the spot. (In the pic below the parts are not yet at their final height. I did a level concrete platform that is not there yet in the photo.)




Then I was on to drenching the fire bricks in water to make the fire cement somehow stick to the bricks and build the heat storage section of the stove. It was actually - and unexpectedly - one of the most difficult things I did on this project. The construction felt fragile at first and only when it was dry did it have my confidence. I then did a test fire, examined the construction and moved on to putting cob on the heat storage and calcium/sand plaster on the bottom and left section. Some chicken wire was added for support.

 

Now, I still have to do the fine cob plaster on the right (not sure yet, if I should spice it up with some color pigment). Plus I have to do the stove (and the walls) with calcium paint. Plus... well, the hut is still under renovation, so more work waiting. But I did of course do some more testing - partly to speed up the drying of the cob, partly because I was just to excited to wait for it to be finished. I have to say, I'm super happy. I added a chimney shortcut in the back to increase the draft in the beginning - even though I have the impression that it draws well even without it. After the initial first minutes of a burn there is no smoke visible out of the chimney, which is great and indicates the clean combustion that is desired. I closed most of the slanted "ash hole at the bottom" with a flat piece of fire brick (for making pizza after the burn) with an opening towards the back. From there and from the front it draws air, but I do not have an opening at the top of the door like Trev. Maybe I will yet build something of drill some holes into the cast iron door - which was actually the most expensive single item for this stove (about 200€).

So, as I said, I did have a few fires already and here are some temperature measurements from yesterday which I find promising:
I don't have a scale but I used three handful of very dry wood (10 years in the woodshed). Using the first half to start the fire, the second one added 1 hour later and 3 small logs another hour later, I have fire burning for more then 3 hours with especially bright flames in the second half of the burn (as the firebox gets hot). Then for about an hour the coals are doing their thing. During the hottest part of the burn, the IR thermometer goes up to 750-870 °C if pointed to the middle of the chamber. I had bursts of 920 but I'm not sure if this is accurate, since technically the thermometer should max out at 900. Since this is not industrial quality equipment, it might be off a little, but I'm still impressed. After the fire burned out, I put  some pizza in the burn chamber with the walls radiating +400°C. It was almost too hot, but I can see myself using the burn chamber for a lot of cooking in winter (which is great because my hut does not have an oven only a hot plate). I have a few sweet chestnut trees on my property and this will make for great evenings :-)
The heat storage (thermal mass: about 200kg of fire bricks, 150kg of cob for thermal mass aside from the 150kg of insulated fire box) heats up nicely to 75 degrees and stays hot for about 8-10 hours before cooling down to "warm". But I will have more details on how long it takes to heat up and how hot it gets now that the cob is dry which was steaming during yesterday's measurements.
The coolest thing however was the temp reading of the burn chamber this morning some 20 hours after I started the fire. I measured 35°C (outside temp 17°C). And this even though I removed the door for some fixing after the fire had died yesterday and it the heat had not been "kept inside". I just put the door back now.
The 10mm steel plate was 320, when I measured it (but I was heating up spare fire bricks on top of it to use for drying a section of a wet wall). I then tried so boil a pot of water, which worked well, but I did not check the time it took.
The exhaust pipe was about between 90 and 150 during the burn depending on where and when I measured. From the chimney only some heat flimmer as visible.

Once everything is done I will make more precise measurements and a list of the the material I used and how much it cost. And I will post the video, when ready. :-)

Thanks Trev and the community for sharing. I would never have ventured to do this without the help and support I received here.

[patamos]

Nice build Jojohannes

[Vortex]

Well done Jojohannes!
The bubbles in the top surface of the casts is normal, if you want a smoother surface you can gently scrape the surface with a trowel about 24 hours after casting.

5mm thinner on the back is no problem. You can skimp on the back, top and bottom, as the bottom of the mold is the inside of the firebox. If you don't completely fill the side molds though the firebox cast don't fit together very well because the bottom of the mold is the outside. The back is quite a thick casting anyway, I've left it 20mm thinner before now and it wasn't a problem.

I would have insulated the stove from the floor and outside walls, and made a bench or bigger bell than you have. You can see in your chimney temps that there's more heat that could have been harvested, but you're happy with it and that's what really matters. Any pics of your bell construction?

Does the door have a fire-rope seal around it to make it air-tight? if so you could experiment with seeing how differently it behaves with it removed. Mine has no seal and a 2mm gap around the top and sides of the door which provides heated secondary air to mix with the outgoing hot gasses. It's very effective for such a simple system.

I have the grate slot covered with a thick piece of 8mm steel, slightly longer than the hole. It allows the fine ash to fall through, but stops hot coals falling through into the ashbox and it can easily be removed for cleaning. It sits above the grate slot like this (cross sectional view), so there's 2 thinner slots instead of one bigger one:
.__.
\..../

I look forward to seeing that video when it's ready

[jojohannes]

Thanks Patamos, I was inspired to use loam (as cob substitute) by your "oven landscape". I may yet color it, but we'll see.

Thanks Trev. It is mostly thanks to you and the plans, pics and advice your shared here that this thing could be built.
I actually did insulate the stove on the floor and the outside walls (except the front) following your recommendation earlier.
I guess in retrospect I could have increased the size of the bell (I'll look if I find a meaningful pic about its construction), but I already made the bell taller and longer than yours thinking the reduction of the size of the metal plate would warrant such a change. But - unexperienced as I am - I was afraid too large a bell would adversely affect the performance. I thought if I had any more loops maybe the temp would be to low for the chimney to draw (I barely fit the 6" pipe). If I had to rebuild, I might make it bigger, but then on the other hand, I have to see how it performs in the winter. It gets very hot for the small hut, I'm trying to heat (2 rooms of 12 m2 on to of each other (one 2 the other 2,4 meters high) + plus some heat for the adjoined bathroom, that generally remains without heating. I guess to make it still more efficient with the build I have, I could add a heat sink to the chimney. What would your recommendation for exhaust temperature be?

I hope I get to the video soon. I still have some work in the house before setting up my workstation and edit the clips. But I'm looking forward to sharing it here.

[patamos]

Thanks Jojohannes,

One thought on how to increase the heat harvest before exit from chimney: If any of the walls in your hut are similarly dense mass as the ones behind the heater, you might find value in thinning the front of the bell chamber wall. The heat will radiate more rapidly but will be partially absorbed by any mass within direct line of sight. The closer the mass the more it will serve as a heat sink. I learned this from building a sweatlodge/sauna with fairly dense light clay walls. The energy from the first round of hot rocks goes into warming up the mass of the building. The colder that mass the more it absorbs. So the effect would be much more pronounced in the colder months.

[jojohannes]

Ok. I'll put the "quick presentation edit" of the video together now. I lost some timelapse footage on the old GoPro, so unfortunately there are holes in the sequence and I have lots of non-important footage instead... I might add a longer version with an audio commentary later and some stills that make following the construction easier. Yet I do hope the upcoming clip, even if this does not explain everything, may at least inspire some people out there to give building a stove a try. After all, I'm a priest and theologian by training not a building expert. So if I can do it, most people out there will do an even better job. In the meantime here is a pic of the semi finished living space with the "Hermit's Hot Hog" at the core of the living area of the brand new "Eremo Sant'Onofrio tra i Cinghiali". :-)

[jojohannes]

Ok, here is the Video mash up of the build:

[Deleted]

jojohannes thanks for sharing.

[wiscojames]

Nice work! A pleasure to watch. I bet you will be pleased with your dragon this winter.

[Vortex]

Wow! Superb work, Johannes.

Thanks for sharing that with us it's a delight to watch

Trev