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Post by dirtcraft on Dec 15, 2011 14:29:11 GMT -8
I'm having some issues with my 6" system (I'm only heating about 100 sq ft in Canada) and I'm hoping you can help. A little bit about the system:
- it's 6" with about 20 feet of horizontal run with five 90 degree elbows in it. It goes up about 4 feet vertically before exiting the building. - there's a 6" steel heat riser, surrounded by a 12 inch steel pipe, which is filled with vermiculite. - I'm using a 30 gallon drum, which has a diameter of 18.5" - I have a 3" gap between the top of the heat riser and the drum (I increased it from 1.5" because it really backed up). - I recently increased the manifold size and ballooned it out to give more room (see picture). The initial tests seemed promising but this is what I'm noticing:
1) The "brick trick" over the feed tube is an absolute necessity on the system, otherwise I get fire climbing into the room. I usually cover 1/3 to 1/2 of the feed tube for it to calm down.
2) The system works best when it's stone cold. I get good suction in the first hour (a nice rocketing sound too) and then things taper off. After the first hour, I usually have a nice bed of hot embers but the wood seems to combust so rapidly and violently that I either get copious amounts of black smoke from the chimney, or the flames simply want to come back into the room. Why am I getting black smoke at this point?
3) Just beyond the manifold I have a T, which faces upward for inspection and clean out and I also cut a 4th opening which leads down into an ash pit. This ash pit always seems to be full of water and, in fact, quite a bit of water seems to be accumulating throughout the system. JSYK, I've fired it about 15 times for a few hours each time.
I took a workshop at Cob Cottage Co. last fall with Ernie and Erica and to my knowledge I've done things fairly well. I'm humbled by these things and would love any ideas people might have. Thanks in advance for your help! Thanks for reading!
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Post by dirtcraft on Dec 15, 2011 19:18:41 GMT -8
Here are a few more photos to give a bit more perspective. Any feedback is very much appreciated. Thanks!
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Post by josephjcole on Dec 17, 2011 20:18:54 GMT -8
There are a lot more knowledgeable people around here than me... but my guess would be that the water is your issue. Could be that the stove is getting hot enough that the water is turning in to large amount of steam and effecting the draft? Even if the water isn't causing the problem it seems like a good idea to find out the source of it and keeping your stove dry. Best of luck, and let us know what you come up with.
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Post by peterberg on Dec 18, 2011 3:12:33 GMT -8
Maybe josephjcole is right. My first thought has been water, still in the bench etcetera. But after stoking it 15 times for several hours the bench should be dried out sufficiently. So, it has to be the moist still in the fuel. Even with bone dry wood, there's water that's bonded into the cells itself. So, your fuel is too wet and/or the bench run is long enough to cool the gases below condensation point. My guess: the fuel happens to be the culprit. The layer of embers you'll get after running the stove for an hour do point in that direction. Ideally, there should be only a minimal build-up of embers. With water inside the fuel the combustion temperature is too low and you'll get a pile of glowing charcoal. The fresh wood on top of that pile is too high in the feed tube and the fire will creep out. The hot charcoal will light the fuel right away, in fact it is cooking the volatiles out at high rate, sending it into the burn tunnel where there's not enough oxygen to react with it. The black smoke you've seen is the result of incomplete combustion. Maybe, just maybe, you'll be able to achieve a better balanced system with the use of a channel plate. Like Donkey's implemented as described in some detail in the small scale development thread. My suggestion: buy a simple moisture meter, split a piece of wood and sample the side which is just split open. The moisture level should be as low as possible, 15% would be nice. The 20' bench run isn't excessively long for a 6" system, but it might be with 5 elbows inside. One 90 degree elbow is the equivalent of 2' straight run, some sources suggest. That could be another cause of all the condensation fluid in the system. Too much condensation is capable to stall the stove altogether. Mark however, apparently not within minutes but after a considerable time of healthy running.
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Post by dirtcraft on Dec 18, 2011 12:10:52 GMT -8
Thanks for your input. I've been primarily burning scrap softwood lumber from the local lumber yard, which I thought would be relatively dry since it is kiln-dried, though, as you said, the excessive amounts of hot embers does seem to indicate that it might not be as dry as I had thought. I think I'll try running some hardwood through it and see how it behaves. I'll let you know how it goes.
I'll also look into the channel plate. Is the purpose to close off some of opening that connects the feed tube to the burn chamber? Does this have a similar effect to covering part of the feed tube?
Thanks so, so much for your input. It means a lot.
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Post by peterberg on Dec 18, 2011 12:40:27 GMT -8
I'll also look into the channel plate. Is the purpose to close off some of opening that connects the feed tube to the burn chamber? Does this have a similar effect to covering part of the feed tube? No, and no. It's sole purpose is to provide a non-interruptable stream of heated air along the ceiling of the burn tunnel. In effect, the situation where there's too much volatiles and too little fresh air in the tunnel would occur not as often. But I'd suggest you read the topic, all the information is there.
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Post by waynem11 on Dec 21, 2011 10:55:10 GMT -8
dirtcraft, Your problems sound almost exactly like mine. It is a fairly new 8 inch system, only about 6 burns. I had a 3 inch air intake 2 feet above the feed tube and it wasn't enough, when it started smoking I would have to open the door to get it going into the burn tunnel. I have enlarged the intake to 4 inches and it has helped, although it seems to me that it could be bigger. I was burning new packing material lumber, 2 x 3 nice looking stuff but it really cracked and popped and there was lots of water drippinng out the cleanouts. I using dried wood now and it helps but I'm still not satisfied. I may try really dry Oak, but I'm still hoping I can use all the scrap lumber laying around. Even with the 4 inch intake I still have to keep the lid on the feed barrel and open just enough to pull any smoke downand still allow a vigorous burn. I also went from 12-14 inch wood to 9 - 10 inch wood and this has cut down smoking some also. I look forward to reading about your efforts.
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Post by canyon on Dec 22, 2011 10:22:23 GMT -8
One thing that happens for the first few weeks of firing a rocket mass heater is that it runs condensate. It really concerned me until I heard that that is normal. Since my first worrisome experience every rmh I have built has run condensate for about two weeks. In fact, when I cleaned the flue runs with a stack brush (after two years) it ran condensate again for several firings. It appears that the light fuzz that builds up in the flue is necessary to prevent the condensate. Just my two cents!
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Post by dirtcraft on Jan 19, 2012 11:47:11 GMT -8
I've done some experimenting over the past few weeks and it appears my main problem was not enough height on the chimney. I've since added 4 additional feet of chimney to clear the roof line and it has made ALL THE DIFFERENCE. I initially had it side vented but now seeing how the smoke clears with the additional chimney length, it appears my structure and the neighbours garage nearby were interfering with things. I guess I never considered just how important the chimney and its location were in creating good draft. I'll be monitoring condensation levels over the next few burns but so far so good. Thanks to everyone for the suggestions.
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Post by rectifier on Jan 19, 2012 19:27:20 GMT -8
This appears to be one of the most common rocket stove problems and it happens all the time. I often suggest more chimney, ESPECIALLY in the case where draft stagnates after time. Read the 'drive behind the drive' thread! A freshly-lit rocket generates a powerful draft in a way that will not be sustained after temperatures equilibrate! The only thing this initial draft can do is prime the horizontal section and push warm exhaust to the final stack so it can start the main draft. The powerful initial suction seems to encourage the view that rockets are "magic" and don't require a proper chimney. Unfortunately, all stoves are powered by draft - and that comes from chimneys. A lot of problems can be solved with a bit more vertical stack.
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Post by spiderstone on Jan 21, 2012 17:13:01 GMT -8
dirtcraft looks real good your finished bench....what are you sealing it with?
Thanks Spiderstone
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Post by dirtcraft on Jan 22, 2012 16:51:59 GMT -8
dirtcraft looks real good your finished bench....what are you sealing it with? Thanks Spiderstone The top is darker only because the plaster is still wet. We hadn't sealed it with anything. Since the photo was taken we finished the face with a fine clay finish plaster and a friend had a futon mattress she wasn't using, so we modified it for a custom fit. We're doing an earthen floor in the space in the spring, after which time we may paint the face of the bench with an alis clay paint to brighten it up. We're sure happy that its running well now though!
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