Any Experience with Kuznetsov Stoves?

I'm surprised of all places to find so little talk of Kuznetsov stoves here. Then again, it's a Russian design, which I recently learned from a Russian speaker here in East Europe. If there are any native Russian speakers who could translate, this video explains in great detail, otherwise for the Anglophones, I came across this.

What I gleaned from the video after a slow translation process, it's a stove that achieves double combustion and a ~93% efficiency by separating the gases released from the combustion, light gases (C + O2) from ballast gases (H20 and N) which are heavier, and when mixed with each other, the maximum temperature isn't reached. Furthermore, the separation of gases and the separate chamber allows for a buildup of oxygen that when in contact with the carbon, from the fuel, causes a complete combustible reaction. One major flaw in traditional stoves is the lacking ratio of oxygen to carbon, hence there are apparently no carbon monoxide reactions within this stove because the oxygen is able to build up. Furthermore, it claims that there's no need for a draft (or hardly any draft, In case I misunderstood).

Here's how it's built layer by layer.

I feel like this should be a separate topic of its own, as the variations are just as boundless as they are for rocket mass heaters.

*Edit* I've added some actual photos from the stove

Hi Maruf;
Did you happen to notice the name Vandenberg on your illustration?
I think that might be one of Peters stoves.
I have heard of the Kuznetsov stoves.  Always good reports.
I think building one of Peters version of a batch rocket and plumbing it into a brick bell.
Would be my choice. As I can build it to fit my space.  

The essence of Kuznetsov's "free gas movement" is incorporated in the "bell" heat exchanger design that is becoming increasingly popular in the RMH world. There are numerous possible ways to configure a highly efficient "reburn" combustion core, one of which is Kuznetsov's. Peter van den Berg and collaborators have developed a simpler form that achieves the same results, verified with professional grade instruments.

I am skeptical of the notion that "combustion gases" and "ballast gases" can be separated in a common scale heater; the gases are thoroughly mixed when entering, and I think all would be heated simply by being in close proximity and the active molecules bouncing off everything in their vicinity. What I do agree with is that allowing the hot gases to rise to the top of the bell and relatively slowly settle to the bottom as they give heat to the container is a very effective method.

No, I'm pretty much a newbie and I wasn't aware Van den Berg is a known variant. I presumed the image was just one of the larger Kuznetsov variants, as it's really complex visualizing a cross-section of a Kuznetsov stove as the latticework and chambers hide other important visual aspects in a 2D photo, compared to this Vandenberg one.

@Glenn, if I understand correctly, I think it's an *effort* to separate the two by allowing the gases to recirculate until they find their way out.

The first image is a Kuznetzov stove, I believe. Peter's batch box design is significantly different in details.

My recollection of the free gas movement discussion is that the "ballast gases" are actually separate. I believe the effect of the coolest gases dropping gets to the same result. There is not a shortage of oxygen in supply air, but generally as the "primary" air supply mixes and starts burning the wood gases, a shortage develops. The "secondary" air supply provides a burst of preheated oxygen-rich air just at the point where a port or constriction causes turbulent mixing, allowing efficient combustion. The same principle happens in both Kuznetzov and batch box combustion cores.

The first picture is from one of my earlier developments, in fact one of my own drawings, years before I adopted the batch box rocket idea. Around 2009 or 2010 I'm inclined to say. Its firebox isn't the same as Kusznetzov's, there's no lattice work at the firebox' ceiling, but a J-tube like afterburner behind it instead.

The heat extraction part happened to be based on what Kuznetsov and Podgorodnikov before him were building, bell-like constructions. In this particular experimental heater I tried to verify Igor's theories, it didn't made any significant difference. Efficiency-wise, as well as for quality of combustion. At the time, I used a Testo 327 to measure what the output of the heater was. The only difference which was evident happened to be the fact that with the so-called "dry slots" open, the chimney temperature went up much more rapidly as compared to closed slots.

On Donkey's forum there's a quite longish thread about what I did and how. In case anyone is interested, here's the link:
https://donkey32.proboards.com/thread/40
and another thread following the above since it was hyjacked more or less by some eager people.
https://donkey32.proboards.com/thread/113

So is the batch rocket burn just as clean and hot as the Kuznetsov per se?

I'm looking for a way to combine: a heating + cooking stove with a narrow stairway and a cuddle nest in a 3x4 meter ovular tiny house. I'm wondering what type of stove design would allow that, while requiring minimal cleaning due to cleaner and fuller burning.

@Peter, thanks for sharing your knowledge! So much information :D

Also, are there any mentions of air intake systems? I heard of designing an air pathway from the outside to warm up as it flows underneath the house before it enters the burn chamber, though I haven't found any information on that.

Yes, a batch rocket is just as clean and hot as a Kuznetzov stove, as long as both are built correctly. It's a matter of which design you find easier to follow.

You can definitely build either style as a stacked double bell, so that there is a warm (but not hot) solid top surface to base a cuddle nest on. Any bell design would want cleanouts so that ash can be removed from the floor once a year or so.

Air intakes are a subject of discussion. Some people think that stoves and heaters should have fresh air piped directly from outside to the firebox, while others think that the firebox should use stale room air and allow fresh air to go into the whole room.
Either way, running a fresh air channel under or past the heater so it is warmed before it leaves the channel is a good idea.

Maruf Miliunas wrote:So is the batch rocket burn just as clean and hot as the Kuznetsov per se?

Kuznetzov's heaters are generally larger than mine, another marked difference is this: my designs are checked over and over again. I spent years and a substantial sum of money in order to be able to come up with hard numbers and test results. Igor's designs aren't measured at all, as far as I know of. In my opinion it's highly unlikely his heaters and the underlying principles are tested at all, it seems to be all theory and told over and over again.

So the answer to your question would be more like: my batchrocket designs are burning hot and clean, my test data are there to back up such a claim. A small number of builders have had their implementations tested and approved for sale within the European Union.

What the numbers and results of Igor Kuznetsov's heaters would be remains an open question.

Maruf Miliunas wrote:Also, are there any mentions of air intake systems? I heard of designing an air pathway from the outside to warm up as it flows underneath the house before it enters the burn chamber, though I haven't found any information on that.

In my experience, outdoor air supplies other than a small open window at the wind side of the house would provide more problems than being solved.
Have a look at this website:
https://woodheat.org/outdoor-air-supplies.html
Reading "The Outdoor Air Myth Exposed" is highly recommended.

Hello, I wanted to build a Kuznetsov stove this year and now read a few negative comments about the dry seam. It seems though that in Russia quite a few of these sometimes huge stoves have been built . You indicate that it will not work properly or you just have not seen test figures?
Thank you.

Probably 30 years ago I ran into one in Mt. Vernon Illinois.   It seemed to work fine.  The owner loved it.

Hi Michael,

Welcome to Permies.

John F Dean wrote:Probably 30 years ago I ran into one in Mt. Vernon Illinois.   It seemed to work fine.  The owner loved it.

Thank you. Good to hear, if anyone has links to discussions of problems with the Kuznetsov design please share. I guess there is as in everything different "schools"...

Rather than discussion of Kuznetsov stove issues, this forum concentrates on rocket mass heater ( mostly J-tube and batch box) designs which are fairly simple and quantified as to what works best.

Back in 2008 https://donkey32.proboards.com/thread/40, I tried to mimic the so-called dry slots in one of my early rocket(ish) experiments. The slots in several sizes left and right, larger and smaller, higher and lower in a multitude of combinations or completely closed.

To the naked eye, compared to no open slots at all, there wasn't much of a difference. The Testo gas analyser could find some though, chimney temperature consequently did rise somewhat quicker with the slots open. And the carbon monoxide content in the exhaust gasses rose to alarming levels, which is a sure sign of incomplete combustion.

Without a gas analyser one could conclude combustion was more complete because of the higher exhaust temperature but in reality it wasn't, rather the opposite. The ballast gases weren't separated from the combustibles (CO being one of the latter) and some amount of the hot gasses produced went straight through the chimney into the great outdoors.

My conclusion at the time: the theory is probably flawed in the sense that the predicted effect was neither repeatable or provable.
The hallmarks of a good experiment are that it is provable, transferable and repeatable. Given the absence of two of these necessarily parameters, it's unlikely it would work according to the theory.

Just my two cents.

Thank you. So it is about claimed efficency and not about faulty planning as far as clogging up or creating other dangerous effects, in comparison to an open fire or standard stoves.
The problem I see with rocket heaters for my purpose is that they are said to be for smaller stoves in comparison to the Kuznetsov types and I want to heat a larger farm house with only one stove. To replace the cast iron stove that is filled every few hours....

Michael Var wrote:Thank you. So it is about claimed efficiency and not about faulty planning as far as clogging up or creating other dangerous effects, in comparison to an open fire or standard stoves.
The problem I see with rocket heaters for my purpose is that they are said to be for smaller stoves in comparison to the Kuznetsov types and I want to heat a larger farm house with only one stove. To replace the cast iron stove that is filled every few hours....

Rocket Mass Heaters can be sized to heat a small warehouse. The real limiting factor with mass style heaters is not the heater itself, but the structure being heated, specifically the structure's energy (heat) loss characteristic, which comes down to how well the structure is insulated, including the R-values for doors and windows.

Mass heaters do best in well insulated structures with an open floor plan. First thing I did, when planning on moving from a steel box stove to a mass heater for my house, was to improve the insulation values and open up the floor plan. Once that project was completed, I then planned and built my Rocket Mass Heater, a 6" system size Peter Van Den Berg batch box. Best stove I've ever run! Very clean burning stove. Cut my firewood consumption from 3.5 cords per winter down to 1 to 1.3 cords per winter, and I'm heating (depending on whether doors to back rooms are open or closed) between 900 ~ 1300 sq. feet.

Michael Var wrote:The problem I see with rocket heaters for my purpose is that they are said to be for smaller stoves in comparison to the Kuznetsov types and I want to heat a larger farm house with only one stove. To replace the cast iron stove that is filled every few hours....

It depends on from which side you are viewing it. Biggest batchrocket mass heater to date is a 25 cm (10")  version and there's a 30 cm (12") double riser contraption in Argentina. That latter one isn't a pure mass heater, built specifically for a community builing. This isn't occupied permanently so a real mass heater would be far too slow for this purpose.
There are some limitations what a mass heater of whatever size could heat, above a consize explanation is offered. Thanks Byron!

In short: to date, the design of the batchrocket combustion unit has proven to be fully scalable. One could wonder what the upper limit would be, assuming there is any.

Peter wrote:

In short: to date, the design of the batchrocket combustion unit has proven to be fully scalable. One could wonder what the upper limit would be, assuming there is any.

Thanks I will take another look at the batchrocket site  to see if I can find a mass heater example that would fit. We have about 170m2 to heat on two levels and we rarely get below 0 degree Celsius outside but the temperature in the farther away rooms has to stay above 14 degree Celsius 😁
Reading about people melting the interior of their rocket stoves or having cracking issues in the fire chamber seems to indicate you really have to find a good plan with mass heating option or know what you are doing.

For anyone contemplating building their own RMH, i.e. especially those that do not have experience working with refractory materials nor woodstove construction, The Rocket Mass Heater Builder's Guide is highly recommended: https://permies.com/wiki/57365/Rocket-Mass-Heater-Builder-Guide