reip
New Member
Posts: 2
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Post by reip on Oct 27, 2014 3:44:30 GMT -8
Hello everyone, it is my first post at this forum and i am really glad that i found it. I live in absolutely off-grid and tiny (6m x 2,5m) trailer in Poland and I decided to build a j-tube rocket mass heater in it. I started building it in late september, because i was busy during summer, using Evans' and Jackson's book and stuff i found in the web. I already know about several mistakes i have made: not so much space for gathering exhaust below the barrel, 4" (12 cm) system and pretty scruffy attitude have led me to several problems, similar to this thread: after few hours, fuel loading place is full of wood coal, there is no roar, smoke is just regular smoke, not even close to steam and mass heater is just a little bit warm in places close to the pipe (this might be also due to the fact it is still not dry, but pipes are just warm even after few hours). Anyway, stove works and heats the trailer, but it's definitely not what i wanted to accomplish. I'm gonna use it this way during this winter, but i want to rebuild it when spring comes. So here are my questions: - is there a way to make 4" system effective? i really don't want to dissasemble whole mass heater, it took me so long to build it... - i tried to search for some easy schemes of simple batch box stoves on this forum, but i couldn't find any stuff to start reading about it and find out how it works. Do you have any suggestions from where to start? - what would you recommend to do with this stove? any suggestions are welcome. I'm gonna post some pictures in the evening, but it's an almost ready stove, so i don't know if it's going to be helpful. Thank you and have a nice day!
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Post by matthewwalker on Oct 27, 2014 8:12:11 GMT -8
Try rebuilding your combustion core/riser with as little mass as possible, and insulate it as best you can. If you don't have access to fancy materials, you could cut your bricks into as thin sections as you can, and rebuild the core, then pack around that with insulative cob, made with clay/sand/perlite-vermiculite-pumice, or whatever you have that's light. Just that process should get the thing going much better, right now it's trying to heat all the mass around the fire and it can never get hot enough to function properly. While you are in there you could enlarge the manifold.
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reip
New Member
Posts: 2
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Post by reip on Oct 29, 2014 3:08:29 GMT -8
thanks for your reply!
That makes sense, if only someone told me this before... If it comes to insulative cob, I have a lot of straw and leca, will it work? Does it still make sense to insulate the parts of combustion core that are outside? I mean fuel injection place, it's getting really hot and works well as a heater, but will insulation of it increase effectiveness? Also, i have another question: Is there a way to cut firebricks without special machine other that angle grinder? It's horrible task to do with it.
Cheers!
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Post by photoman290 on Oct 29, 2014 5:56:25 GMT -8
insulative fire bricks are the light soft ones. it sounds as if you have the high density heavy ones. the light ones are easy to cut with hand saw. it will blunt the saw so don't use your best carpentry one.
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Post by Donkey on Oct 29, 2014 7:26:15 GMT -8
You can use a brick chisel which takes practice to learn and doesn't guarantee a clean cut. You will need to build a "banker" which is a box full of sand to put the brick in for cutting. It insures that the entire underside is evenly supported and the brick is more likely to break where you want it. IF the brick you are working on needs to have a clean finish face, it can be ground or rubbed on another brick.
Old-time brick layers had a way of cutting bricks by whacking them with their trowel. I have NEVER been able to make this work for me, no matter how hard I've tried. There is some kind of trick involved that takes a LOT more finesse than I can muster.
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Post by matthewwalker on Oct 29, 2014 8:15:59 GMT -8
Does it still make sense to insulate the parts of combustion core that are outside? I mean fuel injection place, Yes, it's very important to insulate everything in the system that comes before the end of the riser, so wood feed, burn tunnel, riser. All of it, as best you can. This keeps the heat of combustion on the burning fuel and insures complete combustion. Only after everything is burned do you want to start extracting heat for the home. I don't know what Leca is? Anyone? If cutting bricks isn't going to happen, you can try to create a cast core with your insulated cob mix. It will be fragile in the wood feed area, but if you are handy, once you've used it a bit you will come up with something that works for you to protect that area, or just keep patching it as you use it. It's not a perfect solution, but it does give you good burning performance without investing much.
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Post by PNW Dave on Oct 29, 2014 9:22:44 GMT -8
I found this page, describing LECA- www.leca.ae Leca is initial letters for : Light Expanded Clay Aggregate. Leca consists of small, lightweight, bloated particles of burnt clay.The thousands of small, air-filled cavities give Leca its strength and thermal insulation properties. The base material is plastic clay which is extensively pretreated and then heated and expanded in a rotary kiln. Finally, the product is burned at 1100 °C to form the finished Leca product. Entirely Natural Product Leca is an environment-friendly, entirely natural product incorporating the same benefits as tile in brick form Leca is indestructible, non-combustible, and impervious to attack by dry-rot, wet-rot and insects.
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Post by matthewwalker on Oct 29, 2014 9:59:13 GMT -8
Wow, okay, that sounds perfect. Thanks David.
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Post by smarty on Oct 29, 2014 10:00:17 GMT -8
Sounds like you have come up against the same problem as I did a while back with a 4" system that I was trying to retrofit into an old cast iron cooker. The thing clogs up with charred wood and basically stood working. I built mine out of insulated ceramic shell in the end, and insulated all around that as well, but still without success. The thing just doesn't seem big enough to burn all the unburned wood charcoal before becoming clogged with it. If you find any answers to this problem I'd love to hear back. As things stand I'm thinking of trying to do a kind of 4" batchbox style thing. One thing I haven't tried is building a grate into the bottom of the feed tube, sealed off by a door in the bottom that can be periodically opened and the coals raked out. That would be the only thing I could think of doing. Insulation didn't cure my problem.
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Post by matthewwalker on Oct 29, 2014 10:54:24 GMT -8
Smarty, what type of wood were you using, and do you know it's moisture content? Oak and similar hard woods are notorious for being both difficult to dry and building large coal beds. Oak should be seasoned three years at a minimum, and RMH's are very picky about moisture content. Not doubting your skills, just pointing out something we don't talk much about, but is a major factor in coaling and performance overall.
Edited to add: Also, yep, 4" systems are just plain tough, there's no doubt about that. A small side chamber off the feed like I had in my 8" J makes a good spot to stuff the coals as they build up.
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Post by Dan (Upstate NY, USA) on Oct 30, 2014 1:13:41 GMT -8
@ Donkey, It wasn't the wack as much as the hold with the hand, just like the sand you have to support it just right. That being said I can't do it with a trowel either, but I can with a hammer. Those masons didn't care if the inside was rough they just wanted a clean edge for the outside.
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