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Rocket stove mass heater smoke reburn problems...

Radu Marius


Joined: Jan 31, 2013
Posts: 3
Location: Bucharest,Romania
Hello. My name is Marius, and after discovering the concept of a Rocket Stove Mass Heater and all you wonderful people here, i was determined to try to make such a stove in my workshop (because it's wintertime and i have no means of warming up the place, so i can't really work as much as i want to). Before anything, please read all of my post, because i will try to give you as many information about my system as possible. I started up gathering all that i would need, and got cracking. I even bought Ianto Evans & Leslie Jackson's book "Rocket mass heaters: Superefficient wood stoves YOU can build". So far so good, right? I built a mockup heater outside, following the advice of many people here, and after i lit the fire, i was glad i was doing this outside I'm glad to report that all was working well, the draft was good, the wood was burning ferociously, nu smoke coming up the wood feed no matter what kind of wood i burned or how the wood was positioned. I followed the ratio of the tubing, and all is as it should be (concerning all the pipe lengths and diameters). BUT! the smoke doesn't seem to burn as it exits the heat riser! There is a video on richsoil.com, where someone burns the paint off a barrel, and then puts a simple pipe inside the burning barrel, and the gases REALLY burn like a rocket! Is this how the gases are supposed to burn inside the rocket stove mass heater as well? These are my dimensions: The heat riser is a 6" metal pipe, 35" tall. It has a 10" metal pipe on the outside, and in between it has as an insulator, compacted pulverized refractory bricks with a little bit of clay, just to act as a bonding agent (i had a lot of refractory bricks that weren't good anymore, they would break fairly easily). The thickness of the insulator is roughly 2", equally distributed between the pipes. The burn tunnel is 3 bricks width long, roughly 14", and the inner dimensions are 4"x 4", the wood feed being also 4"x 4"x 7" tall. I've tried making the burn tunnel longer, then shorter, like 1 brick or 4 bricks width ( 4", respectively 18"), and nothing changed, by this i mean that the fire would still burn very well and with no smoke coming back through the wood feed no matter what, but no smoke would burn through the heat riser! There was a lot of smoke... The heat riser makes that rockety sound to some degree, but to no use. I have tried making the heat riser longer,up to 39", but still no improvement. I should note that all these tests were done without the barrel on top of the heat riser. These being said, there are a few questions that i want to ask: First, the heat riser insulation. I've read that in order to burn efficiently, the heat riser must get very hot and stay that way. That's the role of the insulation. But my heat riser gets hot, on the outside, kind of slow. To get so hot that i can not touch it at the bottom, it takes as much as an hour of good stoking and fire burning. To get equally hot in the upper half, it takes as much as 2 hours. Could the insulation cause this? Could this slow heating be the cause of not burning the gases? I remind you that all this was tried without the barrel on top (by the way, i have a 55 gallon steel barrel). The smoke wouldn't burn even after 3 hours of wood burning. Second, the 6" pipe was manually made by me, because i wanted a pipe that was made out of fairly thick metal, the ones that i can buy are really thin and i thought that the metal would burn if it was that thin, especially in the heat riser. So i made the pipe out of sheet metal, and it came out pretty round i should say, and i bolted it with 3 bolts to keep it's form. Now, my question is, could the 3 bolt heads that are on the inside of the pipe influence the burning of the smoke? I don't know what else to do. Does the barrel influence in any way the burning of the gases? I don't know. And i won't be able to test it with the barrel until the day after tomorrow. So, please, help a little fellow that wants to build an efficient stove I want so hard for it to work at it's maximum capacity, because if it works in my workshop, then i can start building one in my house, and stop wasting so much wood with my current crappy wood burning stove (it's my sole heating source and it does a really crappy job)... Thank you and sorry for this extremely long post


"Faithless is he who says farewell when the road darkens..." J.R.R.Tolkien
Peter Berg


Joined: May 27, 2012
Posts: 130
Location: The Hague, Netherlands
    
    4
Radu Marius wrote:BUT! the smoke doesn't seem to burn as it exits the heat riser! There is a video on richsoil.com, where someone burns the paint off a barrel, and then puts a simple pipe inside the burning barrel, and the gases REALLY burn like a rocket! Is this how the gases are supposed to burn inside the rocket stove mass heater as well?

Hi Marius, your post is overly large, and too much questions at the same time. You won't get much answers on that one. I'll answer some questions but you have to follow the book much closer in order to build a succesful stove.
Here's the first answer.
No, a stove of this size will only purr, it should make some friendly noise and shouldn't emit smoke. Forget that video, please.
Radu Marius wrote:These are my dimensions: The heat riser is a 6" metal pipe, 35" tall. It has a 10" metal pipe on the outside, and in between it has as an insulator, compacted pulverized refractory bricks with a little bit of clay, just to act as a bonding agent (i had a lot of refractory bricks that weren't good anymore, they would break fairly easily). The thickness of the insulator is roughly 2", equally distributed between the pipes.

Clay and crushed bricks won't count as an insulator, at all. You have to use a real insulating material, like vermiculite, perlite, very light vulcanic rock, expanded clay (leca) or expanded shale.
Radu Marius wrote:The burn tunnel is 3 bricks width long, roughly 14", and the inner dimensions are 4"x 4", the wood feed being also 4"x 4"x 7" tall.

Both tunnel and feed are far too small as compared to the riser. Maintain the same cross sectional area throughout is the mantra. The tunnel at 14" is too long, make it shorter. The burn tunnel csa of 4"x4"= 16 sq.in. The riser's 6" will add up to 28 sq.in. Tunnel and feed should be at least 25 sq.in., that would be about 5"x5" or 4"x6.25", but not any larger than the riser. Stick to the proportions as mentioned in the book, this isn't gonna work, at all.

Real insulation will slow down heat transfer but won't stop it entirely. The whole of the tunnel should be insulated as well.

Those bolt heads inside inside the riser won't make any difference.
My advise: dismantle your stove and start again, using the right proportions and materials.


regards, Peter
Radu Marius


Joined: Jan 31, 2013
Posts: 3
Location: Bucharest,Romania
Hi Peter! Yes, i'm aware that the long post might scare people off, but i wanted to avoid the situation where people would ask me "did you do this?" or "did you do that?", and me having to respond to every single question, and the topic going unresolved for a good while. I wanted to tell people exactly what i have or have not tried, so that they could get a better idea of the situation. I just thought it would "speed" things along, if you will. Now, about your suggestions, i guess that concerning that video on richsoil.com, that is a whole diffetent story, the pipe was longer and, i think, bigger, the barrel was full of pieces of wood (i think?) and it burned quite furiously, and i don't think it has much relevance to what i'm building. Secondly, the insulation was crushed fire (or refractory) brick, and from what i can remember, Ernie and Erica Wisner showed in a video the rocket mass heater that heats their house, and their heat riser was made out of fire brick. So, i guess that it's really not very different from what i have, the only difference being that my heat riser has also an inner metal pipe, beside the insulating fire brick. Also, the burn tunnel area is all built out of fire brick. I bet that the problem lies with the dimensions that you mentioned. Re-reading the book, i realize now that i didn't really listen to what the authors were recommending (sorry, my bad, as an impacient reader). I will reassemble the stove tomorrow, using the right dimensions. I hope that this will fix the problems, and once finished, maybe i will post a video with the end result. Fingers crossed and thanks for the reply! p.s. : maybe i should stop writing such long novels as posts and stop abusing the comma!!!
Chris Sturgeon


Joined: Nov 13, 2012
Posts: 91
Location: Yukon Territory, Canada. Zone 1a
    
    2
Hi Radu,

Sounds to me like you are on your way to getting your RMH in order.

As a somewhat verbose poster myself, I've found it useful to use the return key to start new paragraphs - neither the tab key nor multiple spaces register when you submit a post.
If you post a dense block of text you will have people reading your info with about as much care and attention as you gave to Ianto.

Speaking of density: be aware of what kind of "fire brick" you are using. Some firebrick is made to add thermal mass to wood stoves. The other, insulation, "fire brick" (more properly kiln brick) is used for insulating kilns or brick ovens. The insulating stuff is very white, very light with large bubbles throughout.
Radu Marius


Joined: Jan 31, 2013
Posts: 3
Location: Bucharest,Romania
Chris Sturgeon wrote:Hi Radu,

Sounds to me like you are on your way to getting your RMH in order.

As a somewhat verbose poster myself, I've found it useful to use the return key to start new paragraphs - neither the tab key nor multiple spaces register when you submit a post.
If you post a dense block of text you will have people reading your info with about as much care and attention as you gave to Ianto.

Speaking of density: be aware of what kind of "fire brick" you are using. Some firebrick is made to add thermal mass to wood stoves. The other, insulation, "fire brick" (more properly kiln brick) is used for insulating kilns or brick ovens. The insulating stuff is very white, very light with large bubbles throughout.


Hi! I agree with everything that you said, and will put it to good use!
See?
Now, the firebrick that constitutes the heat riser insulation was actually not white, nor very light. It was dense and pretty heavy.
Guess it was the wrong kind to use, as you and also Peter said.

But i will give the stove one more try tomorrow, if i have the time, with the burn tunnel and wood feed at the right sizes, but not change the heat riser insulation (i can't afford vermaculite or perlite, it's kind of expensive here, unfortunately ).
If it still doesn't work, than i'll try to somehow switch with other tipe of insulators.

Ok, thanks for the info, i'll post the results as soon as i can!
 
 
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