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Post by D. Anthony Dayringer on Dec 22, 2018 11:23:48 GMT -8
I did not put it in, but I would be EXTREMELY surprised if it was real wool.
Is anyone going to comment on anything other than the carpet? I am thankful for the care, but it seems to be the only conversation.
This is my first one, I got all my info from youtube, this forum, the permies forum, and Paul Wheaton's better wood heat videos.
Is it typical for the draft to put out the fire on these things? I have trouble getting it to burn down to coals. It runs great when its stuffed full, but when it gets low it tends to go out. Even if I partially cover the opening with another brick. If I completely cover the opening with a brick... sometimes the last piece of wood will burn to coals, but not always. I guess I havent tested it, but I feel like it would be smoldering and smoking at that point since i am cutting off almost all the oxygen. Dry bricks dont make the most airtight seal, but fire needs oxygen to burn clean.
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Post by D. Anthony Dayringer on Dec 22, 2018 11:52:14 GMT -8
On another note. (I am thinking about starting another thread for this one, let me know if you think I should)
Because of the space this thing is in. The mass that would make most sense for the room, I believe would be considered oversized for the heater. I do not think I will have trouble keeping the draft going. My heat riser is a few inches taller than the 3x the feed tube that I have seen recommended, and my vertical pipe is right next to my heat exchanger. I also feel like I have too much draft now. Even when cold it can blow out the newspaper I am using to light it if I am not careful.
Any calculations I see rely on the temperature of the exhaust. My vertical pipe is about an inch away from a 300 to 750F+ heat exchange(its def been hotter, but my IR thermometer just says HI over 750F). As long as the heat riser inside the heater combined with the vertical (heated) exhaust has enough power to keep the draft going.... is there anything I would need to be concerned about with an oversized mass?
It seems like as long as I have enough flow, the mass would heat up at the beginning, and as the beginning got warmer the heat would travel further into the mass. Unless there is a really long burn the entire mass might not heat up, but as long as I have flow... I don't see why that would cause a problem... other than being unnecessary mass.
Is there something I am overlooking? or do I just need to make sure I have enough power to keep the air flowing through the system?
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Post by DCish on Dec 25, 2018 6:59:52 GMT -8
Watched your video, fun build! Carpet comments aside, here are some thoughts:
- I've only done a few experimental J tubes, and have never lived with one long-term. Disclaimers aside I, too, found that the airflow through the narrow burn area is quite robust as compared to the flow through a batch box or standard box stove. I think that your experience with it blowing the paper out when starting is not an anomoly.
- re: cracking: it is caused by temp differential, so I would expect there to be cracking in the transition between insulated and non-insulated areas, regardless of material used. I agree with your comment that you should have insulated the entire burn area.
- re: not burning down to coals: the j tubes I've made have had no trouble with that, even the ones that were completely uninsulated. The high air flow through the coal bed had them glowing completely through the coaling phase until they were totally consumed. If you are having leftover coals, I would start first with running a test with wood you know to be dry, then insulate the entire burn area (which you need to do anyway) and compare the results.
- re: mass: a 4" J is a small heater. If you over-cool the gases in an over-sized mass, then re-heat them at the chimney, it should still run, though. The only complication I can think of would be that it might be hard to start, and you might have condensation accumulating in the mass. If it never gets warm enough to evaporate it, it could pool and cause problems. There is a remarkable amount of water in combustion exhaust.
Again, there are lots of folks out there with much more J experience than I, but hopefully these are some useful starter thoughts.
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Post by D. Anthony Dayringer on Dec 25, 2018 13:05:56 GMT -8
I already think the 4 inch is a bit small. Any future rocket stoves will probably be 6 inch minimum. Even if the biggest reason for wanting it to be bigger is so I can get my hand in the burn tube to clean it out.
I think I am going to build the oversized mass one as a test at minimum. But it will be set up so I can easily shorten the pipes if I have trouble. I am going to have a cleanout at the bottom of the vertical pipe, so if I have trouble getting it started cold, I will be able to light a small fire in there to get the draft going.
I think my problem with it not burning down is more to do with the wood than the draft now that I think about it. It was pretty bad with the last batch of wood that I brought in the house. I think it was just too wet.
If it burned enough to turn into coals the coals would be completely consumed.. but if it was still wood it would blow out the flame. Which is why I am thinking it might just be too wet. I really wish I had some wood that was dryer, but this is all I have. Some of it is dryer than others, and I am getting better at spotting what is better.
This thing has already saved us $ and I can't wait until I get the mass built so I am not just pumping heat outside all the time.
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Post by DCish on Dec 25, 2018 14:44:22 GMT -8
My rule of thumb is the wetter the wood, the thinner it has to be in order to burn halfway well -- more surface area helps. My grill conversion (http://donkey32.proboards.com/thread/2301/gas-grill-rocket-conversion) is a 4" J. It is made entirely of insulating materials, but it is still sensitive to wood quality. Once it is good and hot, though, I can put in lower-quality stuff and it will usually have enough residual heat to power through drying it out and burning it, if the bits are not entirely green and not greater than 1" in diameter. Smaller fuel is definitely better with my J-tube.
You might try stuffing insulation into your existing burn box to help hold in the heat that you generate. It will cramp down your already-small burn area, but if you split a 2" piece in half (might be doable, I've played with that stuff before... I always use a respirator when I do, though), you might be able to insulate at least two sides of it and see if that helps. Keep in mind that, for all practical purposes, half-inch ceramic wool doesn't pass heat any more quickly than two-inch wool. The only difference is that two-inch wool means that the heat has to spend four times as long travelling before it reaches the other side and begins transferring to whatever is outside the wool. So a half inch of wool is basically as good as 2" of wool at supporting high combustion temperatures during a burn.
As for mass and tubing, have you considered a dead-end bell bench? Mine (http://donkey32.proboards.com/thread/1448/adding-bell-bench-standard-stove) performs amazingly, I couldn't ask for a better heat harvest setup. You seem to like concrete - you could make a bell out of concrete block with no worries, since only the burn core is subject to high and rapid temperature fluctuations. I'm in my third season with mine (made of salvaged brick), and there is nary a crack to be seen in the joints. If you made a long bell with a removable top it would be super easy to tune it by dry stacking an interior wall and moving it closer to the inlet / outlet end until you hit the sweet spot. Then if you eventually rebuild your core to a 6", you could remove the interior wall and use the full bell. For reference, the internal dimensions of my bench are 14"W x 15"H x 64"L, fed by a standard box stove. I can push the stove as hard as I want (I am sure it puts out more BTUs than a 6" J, though likely a bit less than a 6" batch box) and the exhaust temps coming out of the bell generally coast at around 150-200, with a flat-out, burn-all-day-24/7 record high at or under 250F, if I recall correctly.
As for draft and mass, there will definitely be less draft once you add mass and dump more heat. I can't light my box stove without a bypass (though, to be fair, the exit from the mass is 4-6 inches below the floor of the stove, so it's not too shocking), and there is a definite damping of the draft when I flip the damper to run through the mass.
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Post by D. Anthony Dayringer on Dec 27, 2018 12:37:58 GMT -8
I like the bell bench idea, but it will not work for this build. I already have plans for at least 2 more rocket heaters(and possibly a third). One for my shop, and one outside for cooking... If my plans go correctly the one outside will be a flat top grill, and built so you can make some quick changes and use it as an oven. I think I am going to do a bench in the outdoor one like you are describing. Also my dad is talking about wanting me to put one in his house.... So I will have opportunity to play with some other designs!!
Got some dry wood in it... My problem with it not burning down was wet wood. Burned down to ash even after there was only one fairly large piece left.
The second part of the build will be online tomorrow. I will update the thread when it is.
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Post by D. Anthony Dayringer on Dec 28, 2018 15:40:54 GMT -8
Part 2 of video is up
I also added it to the first post.
Let me know what you think. If there is anything I am flat out wrong about, or anything I should have added, I still havent edited the rest of the build so I can add comment on it in a future video.
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Post by drooster on Dec 28, 2018 16:16:40 GMT -8
Part 2 of video is up I also added it to the first post. Let me know what you think. If there is anything I am flat out wrong about, or anything I should have added, I still havent edited the rest of the build so I can add comment on it in a future video. Love the video! You have very long arms. But ... ...the carpet ... THE CARPET!!
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Post by D. Anthony Dayringer on Jan 8, 2019 13:46:22 GMT -8
Finished the third video, its the heat exchanger. Updated the first post, and here is the link.
The videos seem to be taking longer to finish than the heater! lol
Hopefully I will get some time soon to build the mass. Life continues to get in the way tho!
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Post by D. Anthony Dayringer on Mar 29, 2019 20:04:16 GMT -8
FINALLY finished my last video on the heater build. I still need to build a mass. Its been VERY LONG, VERY HARD few months. Let me know what you think!
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