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Post by northriver on Nov 16, 2010 16:32:19 GMT -8
Hi, I am new to this forum and hope I am posting this question in the right place! I am planning to build a rocket mass heater for my FINALLY closed in house starting later this month (details of our building project can be found at http://www.darfieldearthship.com). I am trying to lay out a basic design for the heater before we start. My question ... is the feed tube/burn tunnel/heat riser assembly more efficient made up as a single welded unit? I found this blog post during my research that describes a steel core for a rocket stove at blackearthrocketstovesblogspot.com/.. Below is an image from this blog. As you can see, the core of the stove is a single welded unit. Does anyone have any experience doing this? Does it increase the efficiency of the stove due to smooth surfaces and no potential leaks? From reading the blog post it seems refractory bricks are fitted around the core. One question I have is how long the steel would last? Also, despite the reduction in flow efficiency would it make sense to oversize the metal core and fit refractory bricks inside the core? That way bricks could be replaced as they fail and hopefully the steel core would never fail. (I suggest this because the Pacific Energy wood stove in my old house was built this way.) Does anyone have an opinion on this?
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Post by canyon on Nov 17, 2010 10:43:47 GMT -8
I hope we eventually hear from someone with experience with one of these blackearth units. I am building my steel/firebrick rocket unit this winter and am glad your question came up. I think it is much better for longevity to have the firebrick on the inside. That is how I am doing mine although it won't be a continuous welded unit. I think that the black earth design will run into some issues with expansion/contraction. It is important in high temp areas that the components can move at their own rate and not break itself apart/warp/deform to the point of problems. I will have a welded steel down and horizontal (with a door with window) feed section lined with firebrick on the inside followed by a firebrick burn tunnel (short) and then a steel schedule 40 pipe heat riser. I will share my experience when I actually do it. Right now I am busy snowmachining in the firebrick so it won't be for a month or two. My temporary unit has worked well but I am looking forward to the more permanent unit with more whistles and bells (the bake oven is what I'm particularly looking forward to). Please share your experience too!
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Post by northriver on Nov 17, 2010 10:53:07 GMT -8
Hi Canyon,
I'm glad to hear other people are thinking about this too!
When you put the firebrick on the inside will you loose fit it, or mortar it in place? My idea would be to simply fit the pieces with no mortar so that damaged ones can be replaced. Any issues that you can think of with this?
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Post by Donkey on Nov 18, 2010 8:17:14 GMT -8
I've only got one comment.. One of the, oh so sweet aspects of rocket stoves is that they can be built for very little money, even totally free (except your own time). Those Black Earth welded jobs look great, and I imagine that they work REALLY WELL.. BUT.. If the guy that makes those values his time, I expect that they are NOT cheap.
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Post by Donkey on Nov 18, 2010 8:20:26 GMT -8
Umm.. as to efficiency, I'm not sure you would be getting more out of that system than any other, besides convenience. The Steel DOES have less thermal mass than a brick system, so if it was well insulated, it would get up to temp MUCH faster.
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Post by canyon on Nov 18, 2010 8:49:02 GMT -8
Northriver, I will fit loose as well in the section that I will line. Loose is the key word, it is important that it is not too tight for movement through the large temperature range.
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Post by grizbach on Nov 18, 2010 11:12:03 GMT -8
Canyon, I'm not sure if I understand your "welded steel down and horizontal (with a door with window) feed section". It gets red hot at the bottom of the feed tube. There will be warping. I have mine made out of stainless and it has a slight buckle to it. I'm on my second season with it, might have to replace it next year?
Northriver, about the picture. I have my doubts about the burn tunnel/grate area lasting. The rest might get many years of service, but this area is under severe heat-stress.
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Post by canyon on Nov 18, 2010 20:49:12 GMT -8
Canyon, I'm not sure if I understand your "welded steel down and horizontal (with a door with window) feed section". It gets red hot at the bottom of the feed tube. There will be warping. I have mine made out of stainless and it has a slight buckle to it. I'm on my second season with it, might have to replace it next year? . I am lining the steel on the inside with full fire bricks with the exeption of the grate which I expect to replace most often. Probably will make more sense when I actually build this and get pictures to post, so stay tuned...
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Post by grizbach on Nov 19, 2010 1:26:21 GMT -8
Makes perfect sense. Looking forward to the pictures!
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Post by Donkey on Nov 19, 2010 8:55:32 GMT -8
huh.. Why line the inside with brick?? I'm not following.. Is it to avoid metal warpage? or.... Usually, I use metal parts to lighten the internals, that is reduce thermal mass inside the burn area for faster heat-up. I use pearlite/clay or some such light-weight insulation to protect the metal..
Well, I think it'll work.. And talk about airtight!..
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