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Post by patamos on Nov 14, 2021 18:36:40 GMT -8
Hi Folks, I'm well into a variation of Trev's 4" cookstove. This may be more like a 5" The fire box is changing shape with standard brick size differences, and it is longer cuz folks around here just don't wanna cut their firewood shorter than 16" vftshop.com/Video/IMG_3184.MOVTowards the end of the video (after I've done waving my hands around about having to beef up the firebox cuz its gonna get abused...) I pose the question of what other builders would do with the heated backrest we are squeezing into a 2' wide footprint (very small cabin...) Please chirp in and let me know what ya recon? And thanks again Trev for uploading the imagery
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Post by patamos on Nov 8, 2021 17:41:08 GMT -8
Thanks Trev
Think I'll try that coin biscuit technique to use 1.25 HHD splits in the fire box. I've seen metal pins in pretty high heat areas of flue runs so could be in safe range. The key will be having a contingency plan if it doesn't work...
Might move the throat forward by however much i lengthen the box from your specs. That way fuel at front isn't too far away. Will keep you posted.
Also, this will be a cook top version with quite a bit of heated bench downstream. So my back pressure equation will have to be adaptable.
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Post by patamos on Nov 7, 2021 10:57:23 GMT -8
Hi Trev, Great to see this thread humming along. I've been out of the loop for a long while (too many projects on the go...) but am now getting ready to do some sort of tiny heater in a friends cabin, so thought i'd check in. And 'voila' here you have the specs for a 4" system. A couple of questions though: Around here people are not interested in chopping their firewood shorter than 16", so i wonder what effect a longer firebox (say 42cm) would have on the overall dynamic? Would you perhaps recommend a longer narrower firebox ceiling port? Or maybe set it forward a little? Also, many stove operators are not as interested in fine-tuning their air supplies mid burn, so my thought is to make the sloping firebox floor as you have, with 1/2" gap down the centre, but also notch in a bunch of small air ducts along the outer/upper sides of those sloping floor slabs... and then have all of that be the primary air supply. I am sure the constant bottom air supply is going to increase the potential for over-fuelling, but with operator error and/or disinterest an inescapable factor... I am inclined to make things as simple and stable as possible. Maybe implore them to lay a big wedge shaped piece of wood into the bottom of that V will help. I look forward to hearing your (and everyone's) thoughts on this. On another note, the other Pat from BC was asking about refractory suppliers in our area. Once upon a time Clayburn based in Abbotsford offered world class HHD and MHD fire-bricks, but they were bought out by a big TExas corporation a number of years back and no longer produce locally. Truth be known, their 110 year old factory/quarry site was subsumed by urban sprawl, and they may have been running out of raw materials anyway. Dave at Improheat in Vancouver is a helpful fellow. And there is another fellow, Heinz Weiduwit at 'Alliance Refractories' who knows his stuff. All three of those companies are importing materials from US, Chech, and China. IMHO, the best people to deal with are 'Alphatherm' back in Ontario. A fellow there named Elvis is super switched on and happy to scurry up anything you may need at a reasonable price. I get all of my MHD firebrick (Alseys from mid west US), 12"x24"x2.5" AL-43 slabs, calcium silicate board, and various other stuff from them. All of the masonry heater builders I know recommend him highly as well. And one more note (seeing as it has been so long): On the matter of how much mass to have in the firebox walls, one advantage of thicker (up to 2.5" say) is that once the fire is out you can pre-load the next day's fuel and the residual warmth will thoroughly dry it out overnight. Makes a huge difference on startup efficiency. thoughts for now
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Post by patamos on Feb 8, 2021 19:47:13 GMT -8
Sounds like a fun experiment in many ways. During the rebuild I think you could also add a lot more harvesting mass without any trouble. Maybe inside the barrel, maybe a surround bench... maybe a steam powered water park... all kinds of possibilities
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Post by patamos on Feb 5, 2021 12:41:10 GMT -8
i also wonder why my barrel and mass is not getting that hot, perhaps the ceramic glass is shedding too much heat, I might try placing some insulation over it .... When i want to shed less heat off the ceramic glass top i sprinkle a 1" thick layer of 3/8 coloured pebbles. This slows the radiant harvest/loss somewhat and makes for a nice aesthetic. Some of the rocks pop the first few times it gets hot but eventually they stop. Of course, this method depends on having a perimeter that is a bit taller than the cook top. I've never tried putting the cooktop-glass in the shoebox innards, but I know that clear ceramic glass starts to crystalize and destabilize pretty quickly at those temperatures. You might get a season out of it before it crumbles. But no harm done...
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Post by patamos on Jan 25, 2021 22:13:12 GMT -8
Trev that is crazy that your kiln shelf has cracked. I have been using them as cook-decks atop 6" L-feed rocket ovens for years now without a problem. Sometimes seriously over-firing for hours at a stretch. And they are of course meant to take a lot of heat.
Could there have been some weird mechanical pressures at play in your set up?
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Post by patamos on Dec 11, 2020 9:12:46 GMT -8
Just last week i opened up a L-feed rocket stove i had built for a tiny home the year prior. I had installed a 5-minute riser using 1/4" ceramic felt lining the inside of 5" dia. 26-guage metal ducting as part of a 4.5" system. The bottom 5" of the riser was in bad shape with the metal disintegrating and the ceramic felt sloughing off. Could be that the metal started going first and then turbulence etc battered the felt. The owner had been running the stove daily through October to April last year and then again this Fall, usually with 1 or 2 reloads. So it was getting pretty hot at the riser base.
Anyway, I replaced it all with I.F.B.s
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Post by patamos on Nov 23, 2020 19:30:40 GMT -8
I could be wrong about the straight application of sodium silicate. The stuff i have used is quite thick, like a syrup, so it didn't soak in much at all. maybe the deep penetration makes a big difference
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Post by patamos on Nov 22, 2020 11:03:03 GMT -8
nice experiment in my experience, adding a coat of sodium silicate or furnace cement to the inner surface of CFB only last a short while. The hard material wants to expand and contract and soon delaminates from its softer substrate, taking a thin layer of fuzz with it.
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Post by patamos on Nov 17, 2020 12:12:18 GMT -8
Ya I think a lot depends on how much heat you have shed upstream. I like to think of worst case extended firing scenarios. Case in point being the Quebec ice storms a few winters back. Durning a cold multi-day power outage people were firing their wood stoves 24-7. Quite a few houses burned down due to chimney overheating nearby combustibles. Perhaps you could test with a concrete slab floating on CFblanket gasket. Otherwise, as mentioned prior, I think brick outer walls with flue liner core is simple enough: www.mha-net.org/docs/v8n2/wildac16f.htmMaybe even running 26guage (or thicker) metal ducting to the far end of the bench will cool things down enough.
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Post by patamos on Nov 14, 2020 18:34:37 GMT -8
No worries Above paving slabs i just apply brown coat (with fibre mesh) and then finish plaster. To get a desired flywheel/lag time for heat delivery, i add straw clay material under the slab, in the space between the flue liner and slab. The further from the fire box, the less straw in the mix to decrease insulative effect.
Concrete holds up okay so long as it does not experience a rapid change in temperature. I vaguely remember Karl saying 1c per 5 minutes. And of course there can be the usual stressors like part of the slab heating more than another area of it...
So, somewhere in any heater there is the point at which you can transition to cheaper materials. I would not use anything other than firebrick or castable refractory an areas above 500c. General rule of thumb with bigger (more powerful) fireboxes is the first 4 or 5 feet downstream from the firebox. Below 500c most any clay brick and flue liner work okay. I'm not sure at what point one can go with straight concrete in contact with the hot flue gasses. But i tend to make sure I am at least 8 feet down a flue run first.
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Post by patamos on Nov 3, 2020 16:40:13 GMT -8
Yes I've done a number of benches with heated backrest. I like to run gasses through the bench to the far end first, then back through a narrow bell chamber backrest. Otherwise the top of the bell closest to the fire box can get pretty hot and there is not much you can do to tweak it. The bell can be built as narrow as 4" and still achieve the desired free-stratification. This works well when using 4.5" x 9" x 2.5" firebrick shiners. For bench materials check out what Max Edelson did a few years back at MHA gathering: www.firespeaking.com/masonry-heaters/rocket-mass-heaters/rocket-mass-heater-cookstove/www.mha-net.org/docs/v8n2/wildac16f.htmThe trick is partially insulating above the flue liner closest to the firebox. If you use concrete slabs to cap you can do it initially with 1/2" ceramic felt as temporary gasket so you can remove the slabs at will for tweaking.
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Post by patamos on Nov 1, 2020 18:03:51 GMT -8
James, ya that should help. I'm curious to hear how it affects the flow.
Martin, Trev is correct. I used stove glass as the roof of my main firebox for a year. Then replaced it with CFB when i reconfigured the set up. I have continued using two small pieces of stove glass (6" x 4") as the shelf between the upper shoeboxes. After 3 years they are getting brittle and starting to flake. Kind of like they are degenerating to silica sand. I also had a 1.5" x 8" stick of ceramic glass protruding into the throat (inverse aryan set up). But under those conditions it only lasted 1 season.
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Post by patamos on Oct 31, 2020 12:02:27 GMT -8
Pat, there's no way to tell whether this artful construction of yours would help or not without rigorous measurements. One can only view, smell and listen and interpret those observations. And as I learned in a very early stage, in the cases I expected a real improvement the Testo didn't agree about 90% of the time. My score is improving over the years, presumably through experience but most of the time I haven't been right in 75% of cases. As an aside, my goal is to implement an excellent working core without much frills, bells and whistles. If I was working on a commercial implementation the story would probably be different. Not a whole lot, but investing a lot of time and money in the finer details of a core that is to be produced in multitudes might be worthwhile. The very devil is in the details, I know that all too well. Oh ya, I understand your point. My only real observational data are signs of smoke coming and going on the glass in front of my upper chambers, and any signs of smoke exiting the chimney (with green forest as the backdrop). That said, both of those indicators have improved as i have found ways to tweak the post-port micro-turbulence. The glass now only ever soots up a bit if i do something silly like try to reload mid-burn and not crack the door to boost O2. I totally appreciate the work you are doing. Just throwing in a few thoughts on shapes related to stream patterns. Wondering what the difference may be between a uniform weir spanning the width of the channel, and a stream bed with boulders protruding. Just one of the ways I tend to nerd out
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Post by patamos on Oct 31, 2020 11:33:38 GMT -8
Hi Patamos, I have been running the stove with about 10% bypass recently which can bring flue temps up to 95 C . I have also made a rookie error in assuming that once the flue gases go past the first exit port that once it stays above csa it will be ok . Recent posts have made it clear the second exit is important as well. When I correct this I am hoping that I will be able to keep the bypass closed. There is also a pinch point where the main body of the stove meets the bench which I hope to improve. James.(cork). James, I'd still guess it is due to the pinch point you mentioned. I say this because the last vortex i built with a massively oversized ISA (see: amosclayworks.ca). 12' of 6" x 9" flue run, opening into 90sq.ft. of bell chamber. It has the low bell exit port as usual, but also an adjustable bell-exit port near the top of the bell into the chimney. The idea was to experiment with major oversized harvesting mass, and be able to tune it back down. At first i had to keep the bypass open about 10%, and the upper bell exit at 40% but after adding another 3' of chimney flue and some pebble rock atop the cooktop surface it can now run with bypass closed and upper bell exit at 20%. All this to say, tuning the downstream gas flow dynamics can be a major factor...
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