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Post by patamos on Jan 9, 2014 22:58:36 GMT -8
Thanks again for your advice Matthew. Deeply appreciated
I hear you about taking it one step at a time re upstairs modifications. Makes sense to err on the hot side heading up. Clarification re bypass location. Planning to T it off the tube leading from down draft into first flue run. Aiming the T upward at 11o-clock to line up with primary and return flues heading towards ceiling. Will place damper in between where it makes sense as the body of the heater shapes up.
love the video definitely a day of discoveries.
A input flue within the bell flue to the far end. Then let the gasses mingle their way back. Very interesting. Thinking about how to sequence the build... maybe set the galvy pipe down on the ground in the belly and cobb it to completion. Then set barrels over top... Definitely worth a go some time or another.
ONe issue coming to mind with the barrels is how to equalize the dispersal of heat through the cobb covering. Seems the crest of the arch is where i'd want the most insulation (say an inch of clay perlite) sandwiched in the cobb over... But this is also the weakest/thinnest cross section of the arch. I think the basic shape is a winner, and i have tremendous faith in the strength offered by a layer of burlap embedded 1/4" to 1/2' from the bench surface. Together they ought to be more than enough. Have your experiences shown you any trouble here?
Thinking now about a rectangular (L-shaped in plan view) bell made of cob and old bricks (of which i have many on hand). And creating a 36" CSA channel along the inner front face going from downdraft exit to far end of bell. It would involve buying a dozen or so 2'x2'x1.75" concrete pavers and building an internal column or two in the L-corner. Slower and pricier to build than the half barrel to be sure. But could be a good way to get the ISA closer to the 40sq.ft. range. Long vertical surface radiating into the room at leg level would be a plus. With the double flue bypass i'm sure i could prime out any cold slugs. How do you think those pavers would hold up with the highish bell-top temps?
That said, I really like your idea of the bell at far end of the bench with flues coming and going. Totally makes sense to let the gasses linger there. Presuming it would be wise to have the return flue exit lower down in the bell... Looks like 6' of horizontal from downdraft chamber to bell with one 90 elbow. Then about 7.5' coming back (further back to the wall and under the stairs) with another elbow. How on earth to calculate ISA?!?!? hybrid shenanigans...
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Post by patamos on Jan 9, 2014 21:26:34 GMT -8
Hi All,
Found this relevant thread after wondering aloud in earlier post elsewhere. Am thinking of a (2) half barrel bell set up in a shortish bench. I've noticed elsewhere Peter VDB recommending roughly 43sq.ft ISA (sans floor) for a 6" J feed with a more vertically oriented rectangular shaped bell. I wonder how the shape of the barrels with the cuts facing down might vary such an equation... If anything reduce it a bit? Or am i just over-sweating the details? I will have a flue bypass from the downdraft exit into 20+ feet of vertical, so am feeling safe in setting my exhaust from the bell right at ground level and tweaking the damper as necessary...
Apologies for a day of mega posting. Feeling a bit twitchy as i just arrived onsite away from home and am needing to adapt in response to a few layout surprises.
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Post by patamos on Jan 9, 2014 18:35:19 GMT -8
No warping so far. And it has run full tilt many times, once for 8 hours at a stretch. I was quite surprised actually. If you cover with fire bricks the metal will not be able to radiate heat as easily so temps will go up. Might be better to go with thicker metal in those layups. 3/8" or 1/2". Oxy-acetaline/propane for the cutting.
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Post by patamos on Jan 9, 2014 16:11:53 GMT -8
Thanks Matthew, Well, after all my mental preparations and lengthy writing, i have arrived on site and found the walls have been framed up differently than anticiapted. I now have no more than 5' of bench space under a stair well for a mass bench before it butts intoa big post, and therefore no way to clean out the intended runs in the backrest. (The post in the right of the pic protrudes 6" form the lath wall to the right and 14 from the wall to the left. I had anticipated the whole wall being flush with the post. So...Your split half barrel approach is now coming strongly to mind and i am wondering how far you got in experimenting with that, and conclusions you have drawn of late. If i recall correctly, you set the infeed port from the downdraft chamber close to but higher up than the exit to vertical. ANd this worked well(?) I can see how i would T- off the infeed port to create the double flue set up. It would occur about 18" behind the flue in the existing temporary set up. The flue would then dog leg forward higher up to go through the hole that has been cut through the ceiling. So long as i place cobb in layers with drying intervals and burlap or fiberglass mesh closer to the bench surface, i think i can build it air tight and strong enough to hold up over the longer term. Might there be any point in extending the infeed channel deeper into the bell area to enhance the heat dispersal? Also i will have 25+ft of vertical flue pulling from above the exhaust port, so i wonder if i may need to slow things down in the bell? .Maybe a smaller bell upstairs (if the ISA needs boosting), or a bit of horizontal routing there if the whole thing wants to pull too fast... Perhaps this should go into a thread titled 'indoor split barrel bell' But for now any feedback will be much appreciated. Attachments:
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Post by patamos on Jan 9, 2014 15:20:43 GMT -8
Further refinement of my P-channel question: Would cutting vertical notches in the side walls of the feed tube nearest the heat riser, and sliding a slab of 1/4" metal down into it to create the P-channel be an effective strategy? Or are the width/depth proportions of the channel more crucial?
Also, does the P-channel need to be covered when the door is closed? I will have 18+ ft of vertical flue above my heater, much of it wrapped in cobb, so it will likely want to keep pulling a fair bit.
many thanks
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Post by patamos on Jan 9, 2014 15:04:17 GMT -8
I am getting ready to do something similar and have been researching back through old to determine what conclusions were reached about Peter's channels at both the front and rear of the feed tube, most appropriate heights of each, and the value in preheating the front (closest to the heat riser) but have not yet located the info. Can anyone shed light on this and how it may or may not be affected by the trip wire in the first or other bricks?
Many thanks for all the experience folks are sharing on this amazing forum!!!
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Post by patamos on Jan 9, 2014 14:47:58 GMT -8
Hi All,
I did a grittle over a 4" L-feed last summer. Searched everywhere for old cast iron stoves with removable plates. Couldn't find them in time (for deadline), so went with a 1/4" mild steel plate roughly 18"x22" set on a ceramic gasket sitting on a rim of firebrick. I left 1/4" of space around the edges for movement, and welded a tab 1"tall by 3" wide across the back corner of the grittle deck. When i want to lift it up for inspection/cleaning i crimp the tab with a pair of sturdy vise-grips and carefully lift the back up with the front acting as a fulcrum. It does take some care to not disrupt the gaskets, but when they do peel up they are easy enough to set back down again - at least so far.
The ISA wasn't anywhere close to a full bell, but the exhaust routing does drop down 3" before entering an area of horizontal flue mass with a surface for pot warming and dough rising.
It is working well so far and is nice to have the more and less concentrated areas of heat in the grittle deck...
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Post by patamos on Jan 9, 2014 8:43:58 GMT -8
I'm looking to build a 6" J-feed system with a non-metal downdraft chamber, and am pondering the best way to go about it. I've seen many pictures of such units operating and am wondering if anyone has experiences/feedback/advice to share. ?? B.T.W.: In an effort to free up photo space for more recent builds, I have moved all photos of this build to: s895.photobucket.com/user/patamos/library/?sort=2&page=1BEWARE of pop ads on that site. Even minimizing them can freeze your computer into a no exit situation. well being pat
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Post by patamos on Jan 9, 2014 8:37:49 GMT -8
Hi All,
I'm interested in anyone's opinion on whether widening the horizontal flue in 90 and 180 bends really matters in a well designed rocket system. Many years ago a grundofen builder/restorer from the Weimar told me to widen the turns so that the flow rate remains as constant as possible... ANd yet i've heard Earnie and Erica say that even 90 degree T cleanouts in the corners 'don't make a difference in flow'. Would it be more accurate to say 'don't make enough of a difference to bother modifying galvy tubes?
The old grundofens tended to have rectangular flues with lots of friction. Round flow way better....
A good rocket heat riser pushes harder than a bigger masonry heater fire box...
Is there anything i am missing here?
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Post by patamos on Jan 9, 2014 8:04:58 GMT -8
Catching up on older threads here as i explore about core options... Carving up an old kiln shelf would be bomber. I did this last summer for the suspended deck of a rocket beehive black oven. On the down side, cutting it eats up diamond tip blades like all get out.
p
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Post by patamos on Jan 9, 2014 7:54:38 GMT -8
Thanks Matthew,
That makes sense. With the intended configuration of things i will have to think of a way to T the two flues from a common down draft. ONe benefit of this idea is that the damper can be further away from the hot gasses, so i can feel more at ease about a standard in-flue unit. The testo numbers from your experiment would be good to see.
I still have a burning question about how best to construct a durable and/but quickly heat shedding non-metal/barrel down draft chamber. And another about whether widening the 180 turns really matters... I think i will load these as separate threads so the time/energy in reading and responding is not so daunting. Many thanks for your help on this. I'll send pics as it takes shape.
p
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Post by patamos on Jan 7, 2014 16:52:01 GMT -8
Thanks Mathew.
I hear you on keeping things simple. So your are suggesting sending all gasses from the heat riser into 6" flue to start with, then T the longer secondary flue off of (and back onto) that. My only thought here would be to cast it all around a sacrificial pipe and use a sliding refractory damper for longevity's sake.
So with the thermometer feedback from higher up the flue stack, the operators can tweak the gas paths as necessary. With the longflywheel sub floor heating system also in the building i don't think things will get too cool. But there will be some seasonal and situational fluctuations. Good to know this is an option in keeping it dialed.
I might look for robax and the like in an old woodstove door...
btw, had fun viewing a bunch of your you tube posts last night. The chickens sure know where it is at...
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Post by patamos on Jan 7, 2014 11:24:59 GMT -8
Hi All,
I am getting ready to build a 6" J-feed rocket system for friends. It will be in a light clay and log post and beam house we built with year-round microhydro that feeds all off peak surplus into a boiler that supplies heat to the bottom and near the top of a 7ft deep sub floor sand bed... So am hoping this heater will be the icing on the cake.
The cabin is 900sqft on the main floor and 500 on the upper floor. Very well insulated with a long flywheel radiant heating system that should take care of most heating needs. The RMH will be there as a more tweakable secondary heat source, a back up cooking system, conductive (bench) heat source and aesthetic comfort.
More than anything i want to make sure it pulls well and is generally easy to operate with as little maintenance/repair as possible. Thinking of high temp firebrick splits for the feed tube, burn tunnel and riser. Maybe a circular cast refractory riser. Question: i have seen and done circular risers with smaller CSAs than burn tubes, eg 6" square burn tube and 6" round riser - does this work because some of the CSA in a 6" square heat riser is redundant? Also, are the 1-2-4 ratios primarily a minimum guideline for riser height? In other words, if i add another 10" vertical to my riser i am assuming i do not need to boost the dimensions of the feed and burn tubes...
Optimizing fast radiant heat delivery is not important so i am looking to skip the barrel and have the flue gasses go from heat riser to a cast iron grittle about 4" above. From there gasses will drop down under 1 or 2 cast refractory joists (supporting the grittle). One route will be up into a primary flue that runs 20+ feet vertically through the rooftop. This will be for a good start up, and possibly for quick cooking tasks.
Sliding a cast refractory damper closed will divert gasses down one side of the stove body with a relatively thin cobb outer wall so that some heat can radiate quickly into the living room. As this small wall surface (2'x3' approx?) will be one of the more thermally dynamic layers of mass i am wondering how best to construct it. The idea taking shape so far is firebrick splits on edge glued with refractory cement. Then 1/2" of cobb plaster. let it dry, check for cracking then another 1/2" cobb plaster with loose weave burlap or fiberglass mesh embedded for mechanical strength. Suggestions/cautions are most welcome.
From there gasses will drop into a zig zag zig zag bench flue with 4 runs. We want the bench for a sitting/lounging/quick conductive warming space... but have only about 7' horizontal area to splay it out. So i am thinking of a run and back in the bench then another 2 in the back rest to tie back into the vertical flue above the damper. I have read that i can expect 30' to 45' of horizontal push from a 6" system. That a circular heat riser will push better than a square. That each crimped 90 elbow reduces that by 3'. But then, the tall vertical flue (mostly uninsulated) run will enhance the pull so long as it still has a fair bit of heat in it. My sense is i will be going for about 30 feet of horizontal. I understand that i need to keep some heat in such a long vertical run otherwise condensation could become an issue. MHA guidelines saying 90c at exit, but that may be overkill. I am planning to wrap the uninsulated flue in 3" of cobb (except where going through floor and roof - insulated double flue there) to make it safe to touch, and to keep drawing heat that can radiate where it is 360 exposed in the upper floor area. So all in all i have a whole bunch of variables at play. I am planning to make my transition from riser to up and down draft chambers much bigger than riser CSA. I am also thinking about widening out the CSA in the 180 bends to even out the flow rates and cut down on eddying. Also making sure the tie ins to the vertical flue are on a 45degree angle. Planning to use 6" sacrificial galvanized pipe so there will be some slicing taping and riveting there... Cleanouts in recesses at bottom of first downdraft chamber, 180 bends at end of bench, and bottom of vertical flue.
The questions most in mind at this stage are:
How much push will i lose/gain by not including the fast cooling downdraft of large radiating (barrel) surface immediately after the heat riser?
What is the best kind of glass for a window in the burn tunnel? Is there a maximal size and optimal placement of this window so that i do not rob too much heat heading into the riser core? How low can i hope to bring my exit temperature without fear of condensation creating resistance?
What might be the simplest ways to tweak the system if i find my exit temps too high/low? One thought is to place the first horizontal flue run about 3" from the front vertical surface of the bench. If gasses are too cold on exit then replace those 3" of cobb with clay perlite. Maybe do the same with areas of cobb that surround the vertical flue upstairs. If gasses are too on exit... then, maybe some sort of mini bell near the the first 180 return.
I realize this has made for an epic read with many questions at play. I had hoped to read/absorb as much of this forum as i could before launching into this next build with not much experience. But man, the rabbit holes are everywhere!!!! So, with the deepest respect and gratitude to all of you who share your knowledge so openly... i cast my wishes into the ethers.
well being
pat
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Post by patamos on Jan 7, 2014 9:54:57 GMT -8
Thanks Donkey
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Post by patamos on Jan 4, 2014 22:43:56 GMT -8
Hey Y'All
Thought i'd chime in on this one as i have been in the business of making finish plasters from scratch of late. What may be common knowledge for most (but not all?) of us is that any type of organic fibre placed that close to the heated surface will burn out sooner than later. The reason for including it at all is to prevent the plaster from cracking while it is setting up. If using jute/burlap you had best slip it first as Donkey suggests and then sandwich it in the belly of the plaster. Also of note, the jute/bulap comes in different grades of fibre thickness and weave density. And the denser thicker fabric is a definite NO for this kind of application as it will leave a layer of separation within the plaster sandwich once burned out. I always go for the looser weave thinner fibre. Coffee shops and distributors are good places to source discarded burlap sacks (from around the world!). When using horse manure or chopped straw i think sifting it through bug screen makes sense. Takes time but gets the manure clumps and straw knuckles out of the mix. Cattails can get clumpy - especially if picked before the seed pods are starting to disintegrate late in the fall.
I checked into this thread because i am researching the prospect of using a whole lot of left over plaster (recipe: 1 part fire clay, 1 part 20/30 grit silica sand, 2 parts 50 grit silica sand, 10% boiled flour paste, 1/4part fine straw...) as the first layer around the horizontal flues i am setting in a 6" J-feed rocket grundofen. Wondering what people think of such a recipe for said application. Also, much of the plaster has gone off (rancid flour smell), which is why i'd sooner bury it deeper in the cob. Any word on the smell getting through 3+" of that much material?
well being
pat
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