Vortex Stove

[Vortex]

The big oven door on mine is only for show - you'll notice it's not in some of the older pictures, I found it in a scrap metal bin at a recycling center a few years ago. I use the firebox as a 'black oven' after the fire has died down.

You should be able to use your old stove top without any problems, all the ones I've made with metal cooktops have worked fine without airtight seals on the lift out pieces. Old stove doors work well as clean-outs. If they have no seals and you want to make them gas tight, get the flat sticky backed fire-rope seal (that they use around the edges of stove glass) and stick it around the inside of the door.

[fig]

Oh I see...lol. Had me fooled. That's a very nice door. I probably don't need an oven anyway. I use a hot air fryer mostly, even more so now that the cooker is broken. I'm not too particular about making things air tight as long as it's not necessary. I get the feeling it may be beneficial if certain things are a little loose.

[jojohannes]

Hi everyone,

I was tuned out for a while and see, that I will have to do some reading to catch up.
In the meantime I just wanted to report, that  with half the winter over, I love my vortex stove ever more. In the mountains here it has not been as cold as further north, but we do get -6 to -8 °C at night. My hut has dirt and stone walls that have a bad insulation value. Further I still have not been able to replace the two old metal doors. So I have to cover them with blankets to keep the warmth in. Then, I discovered condensation in the minimal attic space (50 cm - a false ceiling really, is what it is) between my wood fibre insulation and the roof boards. Turns out between the stone roof and the wooden boards there is a plastic layer, I did not know about. Condensation was thus an obvious problem on the cold surface. So I drilled three 10cm holes for ventilation. This got rid of the condensation, but naturally meant that the attic temperature would be more like the outside, thus providing no longer a buffer. I'm draining heat faster now through the roof. With all this said, and the challenges of heating an old rustico, the vortex stove is doing a marvelous job. I fire it once a day around 2 or 3 in the afternoon. I fill it half and add some more wood an hour or two into the burn. So when dinner time comes around, coals are still glowing and I do my cooking on the stove or in the burn chamber (putting some fire bricks on the coal, as you see in the left image - and, yes as is evidenced by the pic I had to get rid of some paper...I do not normally burn paper).
I let the fire bricks heat up and then do things like mini pizzas or pide and flat bread - a 3 minute job max. For regular bread I have to wait 1-2 hours until it is cool enough not to burn it. In both cases however I have to turn things around midway, because the side towards the door is naturally cooler + through the incline and hole above it receives also less heat from the top.

 

Then I close things up (flue dampener). Depending on the wood I have measured 90° C + temps for the outside of the thermal mass. So during the hottest part of the cycle leaning against it with your back is not recommended. But otherwise the heat is great. It goes straight to the bones, when you come in from a cold winter hike.
In the morning, 18 hours after firing it up, the thermal mass on the right has between 30 and 37 ° C. The steel plate is warm to touch.
I lack a scale, so I don't know how much wood I burn exactly, but I'd say between 12 and 15 kg of mixed wood.
I still hope to do a more exact heat curve, but I thought I post this quick report to encourage people to build their stoves. As you can tell, I love my vortex stove! The only negative I can see, is that on account of it I'm getting fat with delicious homemade pizza. :-(
 

[Vortex]

Hi Jojohannes, Thanks, for the update. Glad to hear you're pleased with the vortex stove, I wouldn't be without mine. I burn about 10-12KG of wood a day, but I'm in a milder climate and my cabin is better insulated.

If you have a bare stone roof in the attic then the cold surface will condense moisture from the air. I guess the plastic layer was someones attempt at a vapor barrier. If you can insulate under the roof it will stop it.

Your stone slab to bake on is a nice idea. What stage is the fire at when you put it in, and do you wait for it to heat up before putting in your pizza or flat bread?

Guess you'll have to do more hiking to lose the weight you're putting on from all that good food

[jojohannes]

Hi,

[deleted off topic section]

The stone slab is actually a flat fire brick. I've used flat granite type stones from the area, but the quarz doesn't tolerate the heat. I put the bricks in, once the coal gets low and there are no big junks left. In that way the bricks don't settle too much anymore as the coals fall apart and the construct remains relatively even (otherwise I loose the cheese). If I put the bricks in 15 minutes before I start backing they reach a good temperature. They also draw some of the heat from the walls, "cooling" them, which makes the oven usable more quickly, since 500°C will burn up the pizza. When the brick reach 250-300° C and the walls have about 400-430° C I strike a good balance.

[Vortex]

I think the problem is the 50cm air gap. If warm moist air can come into contact with a cold surface the moisture will condense out of the air onto the surface. If you had the insulation between the profiles against the underside of the roof it would stop it happening.

Thanks for the baking tips I'll give it a try.

[Vortex]

Replied by PM so we don't get too off topic here.

[patamos]

Jan 11, 2017 18:50:15 GMT -8 1967gto said:

Hey Vortex (or anyone else),
If you cast this per your plans, would skinning it with brick make the mass too thick? I was reading with a regular masonry heater, that if the mass is too thick it makes the stove inefficient.

Thanks

Hi folks

Glad to see this thread thriving

This question of wall thickness around the fire box (refractory core) is an interesting one.  
The first thing to consider is that the chamber is going to expand and contract no matter what.  So having some sort of buffer space between the core and whatever surrounds it is a good idea.  I usually add 1/2" of ceramic fibre felt sandwiched between the core and outer 4.5" brick facing.  I then add 3/4" or so of cob plaster then finish plaster.  This gives a 8"+ wall thickness which is what the ASTM 1602-03 codes call for if we want to be anywhere near combustibles.  

Many masonry heater builders add a layer or two of corrugated cardboard rather than ceramic felt.  And when it burns away an air gap remains.  This offers slightly better insulation, but i am always a little leery of a chunk of brick or mortar getting wedged in there creating a point load.  I live in a high seismic zone so this concern may be less for other regions.

With the last vortex i built both the downdraft chamber into the bench and the first couple feet of bench get hotter tha i'd like, despite being over 5" thick with 1/4" of ceramic fiber felt in the middle.  I will remedy the downdraft chamber by adding another 1/4" of felt on its inner surface the next time i drop by to service the heater.  This worked well on the previous vortex with bench i built 2 years ago.  

But remedying the bench overheat is a bit more of a trick.  I can add more bricks to the bottom of the flue run to speed up the flow of gasses through that area, bit i also have to be careful not to create a gas flow restriction in the elbow between the downdraft and horizontal run.  Also, much as faster gas flow (through a smaller flue run CSA) will decrease the heat exchange in that area of mass somewhat, adding mass to the bottom does not thicken the top of the run (bench seat).  So it might still want to be a bit of a warmer spot

The next time i build a vortex with long bench i think i will build the first 2 or 3 feet of bench flue run with galvanized ducting encased in thermal cob, much like Ernie Wisner and co do with their rocket mass heaters.  This will make for a slower heat transfer into and out from much thicker mass in that area.

That said, i am not bent on even distribution of heat through out the bench… as i think there is value in variety so that different people can connect with less or more heat as desired at any given time...  I just want to make the whole thing bearable, with about 40% in the butt and 60% in the backrest (bell chamber).



 
 



 

[Vortex]

Hi Pat, Good to see you back, hope you had a good break.


I'm finally starting to make some progress on my new stove. It's taken a lot longer than I'd hoped, due to difficulties getting all the materials I wanted, and unusually good weather keeping me working outside.

Most of the metal framework is made now, I hope to start putting the stove together over the weekend or early next week. I'll post some pictures as I go.

The thermal battery end of the stove is based on dense firebrick and storage heater bricks. As you can see the sizes fit together perfect, so I can easily configure it as a bell, mini bells, labyrinth or channels, and see how each behaves.

[fzurzolo]

I always envy people who can work outside in January. We were down below -30 C for a few days last month. But at least it makes my wife want a masonry heater all the more!

I have a (hopefully quick) question regarding the vortex heater firebox vs a standard batchbox rocket. In the vortex, you are suggesting using dense fire brick (retentive not insulating) to get the firebox up to temp over time while most rocket designs suggest insulative brick (in riser I realize) to keep the heat in the gas stream for secondary burn purposes. Does this suggest that the vortex is not designed for secondary burn? There was some earlier discussion on this thread about air leakage around the door providing "accidental" secondary air and burn. No testo work has been done but would you expect this to have less thorough combustion as a batch rocket? Or does it just take longer to get there because the firebox has to get up to temp before really efficient burning, not just the gases like in a rocket?

I recognize this is not apples to apples comparison and there are other design aspects not usually considered in rocket stove design(fire watching, functionality) that were considered for the vortex stove... but any clarification on this is appreciated. Thanks!

[Vortex]

I always envy people who get a real summer. The West coast of Ireland gets very mild winters, but the summers often aren't much better. It can be 12*C any day of the year, and some years midsummer's day has been colder than midwinter's. The damp climate can often make it feel colder than it is.

I've only ever built stoves with dense firebrick. The dense/insulating question is one I hope to understand better myself. My new stove build is designed to make it easy to switch from one to the other, plus various combinations of the two, to see how each affects the burn characteristics.

All firebrick will absorb and retain some heat, but highly insulating firebrick can mostly only reflect back the heat directly coming from the fire, so there is going to be a period at the beginning and end of the burn where the efficiency is lowered. Dense firebrick takes much longer to heat up to the temperature of the fire, but from that point it assists the burn by radiating the stored heat back into the fire, so the period of lowered efficiency at the beginning is longer but the stored heat keeps the burn efficient right to the end. As the saying goes, what you gain on the swings you lose on the roundabouts.

In the Vortex stove secondary combustion can be seen happening around the top of the door and throat. I'm sure this can be improved upon though, so in the new build I'm going to make an insulated secondary burn chamber above the firebox and experiment with various heated secondary air supplies.

[fzurzolo]

Too true. We do get killer summers here (albeit short ones). The +40 C highs to -40 C lows over 12 months makes for exciting times for sure

Thanks for the quick response. That makes sense over all. I think the benefit of the hot and radiating firebox for slowing down the fire and still getting a clean burn is one of the big factors I am interested in. I'm looking forward to seeing how your experiments go and will be continuing with some of my own once weather permits which may come as early as March this year according to Canadian groundhogs. But they were wrong last year, so who knows.

[matthewwalker]

Feb 3, 2017 10:50:35 GMT -8 Vortex said:

All firebrick will absorb and retain some heat, but highly insulating firebrick can mostly only reflect back the heat directly coming from the fire, so there is going to be a period at the beginning and end of the burn where the efficiency is lowered. Dense firebrick takes much longer to heat up to the temperature of the fire, but from that point it assists the burn by radiating the stored heat back into the fire, so the period of lowered efficiency at the beginning is longer but the stored heat keeps the burn efficient right to the end.

This is the standard line, but I'm wondering what has formed your opinion in this case Vortex. You've observed lower efficiency at the beginning and end of a burn with insulated materials? You've experienced better efficiency with dense materials? I'm curious, as my experience is otherwise, and I would like to explore this common belief.

[Vortex]

Hi Matt,

As I said above I've only ever built with dense firebrick. I wasn't even able to get any IFB until recently, so it's only what I've read and seen online. I'd be very interested to hear what your experiences are. Have you used the 2 types in the same firebox and observed the differences?

In different situations they're going to behave differently, for example; If you have a dense firebrick firebox that is well insulated on the outside, that's obviously going to behave differently to one that has a huge mass of cold masonry around it, so I don't think it's as simple as just 'dense vs insulating'.

I suspect there is a perfect balance point of just enough dense firebox lining, well enough insulated from the surrounding masonry to act as a heat reservoir, but not too large to heat up fast enough at the start of the burn, but holds enough heat to tide it over to the end.

[Vortex]

Feb 3, 2017 11:01:32 GMT -8 fzurzolo said:

Too true. We do get killer summers here (albeit short ones). The +40 C highs to -40 C lows over 12 months makes for exciting times for sure

Thanks for the quick response. That makes sense over all. I think the benefit of the hot and radiating firebox for slowing down the fire and still getting a clean burn is one of the big factors I am interested in. I'm looking forward to seeing how your experiments go and will be continuing with some of my own once weather permits which may come as early as March this year according to Canadian groundhogs. But they were wrong last year, so who knows.

Today is the first day of spring in the old Celtic calendar. The mid point between the Winter Solstice and the Spring Equinox. My pond is full of frogs and frogs spawn, and the Daffodils are just staring to bloom, so hopefull the Groundhog was right