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Post by daniel on Jan 4, 2016 8:29:09 GMT -8
I want to emphasize what the other have said, choose a rocket or a batchbox design, do not combine the two designs at this point, choose a heat accumulation system either bell or flues (do not combine). If you choose flues do not make that many bends under any circumstances since you will loose draft. If you choose bell design keep the basic principles; total internal surface area, entry and exit to be system size and entry a bit above the level of exit to avoid hot gases being sucked right into the exit, entry and exit should be as much opposite to each other as possible. A cheap easy way to make a bell, I have just read here on this forum of a half barrell design covered with mass, clay stones,etc. I would raise that half barrel higher from the floor level to have more separation space for the gases. Peter has designed a bell system with two (or more) barrels over the raiser if you want to go vertically, you could cover this with mass partially or whole. It is important to understand the difference between a flue system and a bell. Keep it simple and efficient. Good luck
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Post by peterberg on Jan 4, 2016 9:40:00 GMT -8
OK Dustin, I get it now. I think. Your pictures didn't show a complete heater so people get the wrong impression of your build.
The biggest problem is the riser which is coupled with a bare pipe to the base of the bell. This isn't the right way to do it, it acts as a restriction. A barrel over the riser is a much better solution to steer the gases over a 180 degree direction because it'll give much more space. I would suggest you place a barrel over the riser with a really generous top gap, skip that downdraft pipe and use a hole like that bell base as a spaciously manifold.
But first and foremost, install a decent chimney stack. 99.9% of rocket heaters need that vertical chimney in order to create a high enough gas speed. I expect it'll work when this is implemented.
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Post by dustinmattison on Jan 4, 2016 15:10:41 GMT -8
Thanks for all your help. I am glad I found this forum. Otherwise I would be really lost. I will make some modifications and try again!
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Post by dustinmattison on Jan 4, 2016 16:39:06 GMT -8
peterberg at what barrel height would a system be considered a bell rather than a barrel? The 2 seem to overlap in function, for example if my barrel is 6 or 12 inches above the heat riser, is that a bell or is it still a traditional barrel set up? Could you build a hybrid?
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Post by peterberg on Jan 5, 2016 2:54:03 GMT -8
Tough question. Actually, only the part which is above the riser qualifies for a true bell. Whether or not the rest of the barrel works like that is depending on how much space is left between the riser and the barrel. More space means lower gas velocity so more heat is dissipated to the wall of the barrel.
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Post by dustinmattison on Jan 5, 2016 4:11:28 GMT -8
peterberg Should I put a 6 inch 1 meter tube at the top of my chimney, or just leave the whole thing as 8 inches? The stove is 6 inches and the flue is 8 inches.
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Post by dustinmattison on Jan 5, 2016 4:14:34 GMT -8
daniel With a bell can you also get benefits from heating a bench with a flue, or is it mainly only for radiant heat into the room? I want my bench to accumulate heat using the thermal mass. That was my dream all along, to have a warm bench that lasts for hours after the fire has gone out. I already built the bench and it has several turns in it. I can try only using half the bench if I find there are too many turns. Dustin
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Post by daniel on Jan 10, 2016 4:22:21 GMT -8
Hi Dustin.
Of course you can have a bell configuration that continues with a bench built as a bell to accumulate heat in its mass but you have to understand that there are very important differences between a bell configuration and a flue and combining them without understanding the principles could result in a heater that does not draw and thus have poor combustion etc. Like Peter said, in a bell the bigger space around the riser makes your velocity of gases slow down so by putting a long flue with many bends after the bell you will lose draft and you might not have proper combustion. I would not put flues after the bell. I understand that you want a bench and I think is a great idea, here is what I would do: put the bottom of a barrel 30 cm (or higher) above the riser, cover it in thermal mass, leave around 10cm (4") or more space around the riser to the bell and continue with two half barrels laid horizontal (as a bench) which are installed on a row of standing bricks raised from the floor and cover the half barrels in thermal mass. The floor should be very well insulated especially if you have a concrete floor. The exit to the chimney should be system size 6" or 8". You should not have a chimney which hase a sectional area smaller than your system. Insulate the riser and if possible I would enclose the firebox into the bell. The most important thing is to understand that the combustion is determined by all this arrangement, firebox, heat accumulation area, chimney and they all work absolutely toghether.
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Post by daniel on Jan 10, 2016 4:24:39 GMT -8
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Post by dustinmattison on Jan 10, 2016 17:03:58 GMT -8
peterberg and daniel I did another test this weekend. Not a bell, but the barrel and flue set up. I have 2 or 3 inches of space above the heat riser (the space between the heat riser and the barrel). The flue is about 25 feet long inside the bench. The bench has one 180 degree turn, one 90 degree turn, and about 3 turns which are about 50 or 60 degrees. The chimney is about 12 feet above the heat riser. But still it isn't running well. I assume there is not enough draft. In order for some draft to occur I have to open the batch box door and only fill the box about 1/4 full. Even then, there is still some smoke coming out of the p-channel. There is a lot of ash accumulation and incomplete burning. The barrel doesn't get that hot. After burning for 2 hours the room doesn't feel any warmer and the thermal mass is still cold. How do I troubleshoot this problem? 1. Am I burning the wood properly? Is there a special method for burning in a batchbox? How much should I fill it? 2. Is the flue too long with too many turns? My next test should be to exit the gasses directly to the chimney without going through the bench. If that solves the problem, then I will have to settle for not using the flue and instead put a half barrel on one side of the bench and get the benefits of a warm spot, rather than a complete warm bench. (my bench is 12 feet wide) 3. What if I installed a fan somewhere in the system? 4. Would adding more space above the heat riser help? Dustin
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Post by dustinmattison on Jan 10, 2016 17:28:56 GMT -8
Hi Dustin. here is what I would do: put the bottom of a barrel 30 cm (or higher) above the riser, cover it in thermal mass, leave around 10cm (4") or more space around the riser to the bell and continue with two half barrels laid horizontal (as a bench) which are installed on a row of standing bricks raised from the floor and cover the half barrels in thermal mass. The floor should be very well insulated especially if you have a concrete floor. The exit to the chimney should be system size 6" or 8". You should not have a chimney which hase a sectional area smaller than your system. Insulate the riser and if possible I would enclose the firebox into the bell. daniel I am trying to visualize this. Do you have any pictures or examples?
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Post by daniel on Jan 10, 2016 21:53:09 GMT -8
Hi,
First I want to say that your flues seems to have too many turns and perhaps too long. What is the flue size? I would try it without the flues first like you said and determine if you have enough draft. Do you have a chimney, how wide, how long? Is the riser insulated and what is the space between the barrel and the riser?
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Post by dustinmattison on Jan 10, 2016 22:54:49 GMT -8
daniel the flue is 8 inches and the batchbox is 6 inches. The flue is made from cardboard which was used to mold the cob without straw. Inside the flue it isn't perfectly smooth because where I connected different cardboard tubes there is a rough area. The chimney is 8 inches. It is 12 feet taller than the heat riser. The heat riser is insulated. The heat riser is a little taller than the recommended specs, about 4-6 inches taller. There is about 2-3 inches of space on one side of the barrel (between barrel and heat riser, and about 6-8 inches of space on the other side. Dustin
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Post by daniel on Jan 10, 2016 23:16:01 GMT -8
Now I suspect the main problem is the length of the flue and the bends, altough the there are many thing here that should have been done differently ,like keeping the same CSA throughout the system and perhaps keep a 2" space around the barrel, despite all this I think now the problem is in the length and bends of the flue. If you try and connect it directly to a chimney I suspect it would work but you have a very short chimney (mine is 8" for a 8" system and about 24' high) for this arrangement. There are other questions about the batchbox construction as far as the dimensions, port size. As far as starting the fire I tried different things and the best that worked for me is to stack from smaller to bigger pieces of wood on top and try to light it underneath and toward the port, after this you should try not to open the door too much until the batch is burned and you reload. This would keep the temperature up.Also the primary air through the door I found it better to be somewhere in the middle at the bottom of the door.
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Post by daniel on Jan 10, 2016 23:22:54 GMT -8
I don't know how hard it is for you to change the flues but I would reccomend you try to change that to a half barrel bell, you will get rid of the bends maximize the heated internal surface area and benefit from the stratification of gases inside since you have already slowed the gases down a bit by introducing 8" flue after a 6" system. The half barrel system is simple put 2 or 3 half barrels in a row horizontally and cover them with mass like in a bench, the entry into the barrels a bit higher than the exit and both entry and exit to be system size. Before you do any of this connect the heater directly to the chimney to see if you have the draft, I have not seen your heater and there might be other problems with it.
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