tmac
New Member
Posts: 3
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Post by tmac on Oct 4, 2014 14:50:35 GMT -8
build a rocket stove , in high winds i get a lot of back draft and the house fills with smoke also a lot of water drainage . Lay up a 6.5"x6.5" J burn chamber 13"deep x 32long 49.5 tall witch is only 2.5 " to the top of a 55gl. barrel exit in to 6" round duck work lay in concert bench. Duck work is 24"to a clean out, u around runs 5' along a back wall 90 turn TO 7' run to a 90 turn to a 2nd clean out 24 " to the up turn to exit the room.
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Post by byronc on Oct 4, 2014 16:36:18 GMT -8
A typical 6" system will have a CSA of approximately 30", whereas your 6.5x6.5 J's CSA is 42", slowing the venturi effect of the gases through the J, when coupled to a 6" exhaust. The burn tunnel length of 32", if that is the interior length front to back, is a little longer than one would normally use. Typically the burn tunnel should be 1/2 the riser height, or 24" tunnel for a 48" riser. But yours is only a little longer, so it may be okay. Partially closing off the feed (use a brick slid across the opening to partially block it) to adjust the combustion air may improve the drafting characteristics. What is the inside diameter of your riser? How tall is your chimney? Generally, you want the chimney taller than the tallest part of your house, or any nearby objects, by 3' to 5'. A really good chimney system will force even a problem stove to draft well, in most cases. Moisture is normal in any new RMH that has yet to dry out all of its masonry and or cob. Depending on how it is built, the stove may have to be fired daily for several days to a week or more to completely dry it out. If the stove is fully dry, moisture is then an indicator of either an inefficient burn, or excessive moisture content in the fuel (wood), or both, or too cool of an exhaust to force moisture up the chimney (to much heat being extracted by the thermal mass). Also have a look at the following info concerning the "manifold" area, to be sure it is large enough: donkey32.proboards.com/thread/337/helpful-hint
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JJ
Junior Member
Posts: 56
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Post by JJ on Oct 4, 2014 22:03:15 GMT -8
At the end of your burn chamber, do you have a sharp 90 degree turn between it and the heat riser? If it's curved, back draft can occur. Also, at the end of your flue outside, have you tried a curved elbow joint that points downward?
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JJ
Junior Member
Posts: 56
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Post by JJ on Oct 4, 2014 22:07:02 GMT -8
Oh ya - also, your heat riser should be at least twice the length/height of your burn chamber. So from the bottom of your burn chamber to the top of the riser, it should be at least 64 inches tall. You really need that "rocket" suction and the riser is the most crucial part of that function. The higher your riser, the more suction you will get.
Also - right out of your combustion chamber, have you used a manifold before running your line to the thermal battery? On my first rocket mass heater, our suction wasn't as good and Kirk gave me some advice on getting a manifold on it and it worked out beautifully after that.
Do you have a pic you can link here?
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Post by gerald on Oct 5, 2014 14:52:06 GMT -8
build a rocket stove , in high winds i get a lot of back draft and the house fills with smoke also a lot of water drainage . Lay up a 6.5"x6.5" J burn chamber 13"deep x 32long 49.5 tall witch is only 2.5 " to the top of a 55gl. barrel exit in to 6" round duck work lay in concert bench. Duck work is 24"to a clean out, u around runs 5' along a back wall 90 turn TO 7' run to a 90 turn to a 2nd clean out 24 " to the up turn to exit the room. I know that the 2.5" is about the size that all the books call for but they do not account for the laminar flow of the gasses as they exit the riser. you need to add about 6%or more to the gap. A large gap 2 drums high works well. you can see the same effect with a water hose that has an open end if you turn it up with the water running the water will rise a few inches before there is a loss of the profile and the water starts to fall back any restriction before the apex will create back pressure. also the exit under the drum must be larger then the exit pipe to allow the gasses to turn without running into the gasses coming from the other side of the drum There is a post that tells how to calculate the opening.
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tmac
New Member
Posts: 3
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Post by tmac on Oct 5, 2014 16:45:06 GMT -8
Thanks for all the fed back . I used 2.5 x 4.5 x 9" fire brick butting them upend to end to make a square box which 11.5" out side and 6.75" in side. J tunnel inside tunnel length or (I.T L) is 13.5" down the front 34" cross the bottom and 49.5" up the other side. If i understand correctly the (i.t.L) of the up run need to be a min. of 68" tall. I'm only 18.5" short. right? i also will move the chimney up passed the roof line. i cant seem-to up load pic. at this time. thanks again.
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Post by gerald on Oct 6, 2014 8:53:50 GMT -8
Thanks for all the fed back . I used 2.5 x 4.5 x 9" fire brick butting them upend to end to make a square box which 11.5" out side and 6.75" in side. J tunnel inside tunnel length or (I.T L) is 13.5" down the front 34" cross the bottom and 49.5" up the other side. If i understand correctly the (i.t.L) of the up run need to be a min. of 68" tall. I'm only 18.5" short. right? i also will move the chimney up passed the roof line. i cant seem-to up load pic. at this time. thanks again. no no the J needs to be a ratio of 1,2,3 feed 1 burn 2 riser 3 the gap above the riser needs to be more then the books say by about 6% based on steam profiles. what I ment is that you will most likely never get to large of a gap several feet will work well. to short you get smoke back up.
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Post by Donkey on Oct 10, 2014 9:40:44 GMT -8
1:2:3 is a minimum value and can be used IF every other part of the stove and heat distribution supports it (bench/heat use above fire box, tall well heated chimney, etc.) What is emerging as the more fault tolerant and resilient ratio is 1:2:4. There is certainly room for wiggle in between those figures, but as a general rule the taller riser is more desirable.
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tmac
New Member
Posts: 3
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Post by tmac on Oct 10, 2014 12:28:30 GMT -8
Thanks again for all the feed back!! I broke it down and shortened the run to only 24.5" keeping every thing the same. j tunnel is 13.5 down 24.5 across 49.5 back up burning very well . the next one i will plan a little better. now its time to stone it.
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Post by gerald on Oct 12, 2014 1:21:38 GMT -8
1:2:3 is a minimum value and can be used IF every other part of the stove and heat distribution supports it (bench/heat use above fire box, tall well heated chimney, etc.) What is emerging as the more fault tolerant and resilient ratio is 1:2:4. There is certainly room for wiggle in between those figures, but as a general rule the taller riser is more desirable. Thank you Donkey as I missed the updated ratio.
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Post by erikweaver on Nov 21, 2014 9:34:38 GMT -8
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