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Post by swizzlenutz on Oct 28, 2009 11:52:18 GMT -8
I have plans to make a rocket stove in the very near future. I have a few obstacles to face though. First the land is rented so nothing permanent. The whole thing will most likely be built using mainly bricks.
Brick Question: Fire bricks are needed due to the higher temperatures that will be created, but how do they hold heat compared to regular bricks?
My idea here is to use fire bricks where the most intense heat is and regular bricks for the rest. My original plans were to heat water and release the heat from the water at night, but that requires special plumbing skills that I lack and potential freezing issues or a lot of antifreeze so I think I'll stick with brick.
Another brick question: Would the secondary bricks be better as whole bricks or the ones with holes? My thoughts are that they would heat up quicker with the holes but also lose their heat faster.
For an outdoor setup I plan on making the stove and then around it a cinder block house. Nothing cemented together and probably all less then 5 feet tall. Around that would be a mini shed with the chimney.
My idea is to heat up a mass of bricks and then take the heat that is created between the cinder block wall and the rocket stove and pump that into the house. Maybe through an open vent pipe with a fan or even possible through the dryer vent. Right now the dryer hose is pulled up to add heat in the house when we do laundry and I plugged the hole in the wall with a little insulation. The idea here is to add a little extra heat in the house especially when it starts to hit the negative digits. I am pretty good at finding free wood here and there all year long and I thought that this would be a good way to save money on fuel and keep the house just a little more cozy at night. It'd also be nice to have a backup system in case of a power outage. Swizzle
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Post by Donkey on Oct 28, 2009 18:22:50 GMT -8
I have plans to make a rocket stove in the very near future. I have a few obstacles to face though. First the land is rented so nothing permanent. The whole thing will most likely be built using mainly bricks. Brick Question: Fire bricks are needed due to the higher temperatures that will be created, but how do they hold heat compared to regular bricks? Depends on the firebrick. The more insulative, higher heat variety tends to heat-shock more than others. In fact, I've found that old, red brick heat-shocks less and crumbles less than almost any kind of fire brick. The hottest part of the stove, where you need more heat resistant materials is the back of the burn tunnel and the heat riser. These parts need to be as insulated as possible. It's hard to put a definite R value on any kind of brick. Just to say that the lighter the material, the more insulative. Dunno about the bricks with the holes.. Interesting. So, since yer renting, your idea is to build an impermanent, removable furnace shack and pipe the heat into the house. You want to build as heavy an internal structure as possible to act as a heat battery. Cinder block can work, though personally I'd build it out of adobe brick with a VERY high sand content and use cinder blocks as foundation (lay foundation blocks on their sides and pack their voids with something insulative or leave them open and cap their ends, air trapped inside will insulate) . Through the adobe structure you would pipe the exhaust from the rocket stove and the air pipes for moving heat into the house. Around this structure, you will want to insulate as much as possible. You can use a fan to pump air into the house. With an active heat mover (fan) it would be best to pipe heat to the lowest possible place inside, near the floor somewhere, it will then rise in the home, heating as it goes. You can create a passive thermosyphon arrangement, for times when the power goes out. Arrange your ducting so that air moves outside and into your heat-shack from a low place in the house, to a low place in the shack. A second pipe, from a high place in the shack to a similar elevation (or better yet, higher in the house would return heated air into the house. When the power is on and your using the fan, you could blow out the bottom pipe, taking air from higher in the house and returning it low. When the power goes out, heat would still get to the house, it would just flow in naturally through the higher connection. Huh.. Thinking about this has me a bit excited. It's always fun for me to puzzle out stuff like this. Maybe I'll do a drawing of what I'm thinking and post it...  |
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Post by swizzlenutz on Oct 29, 2009 4:03:40 GMT -8
You know I never thought about using this as a passive system just like you would with a solar thermal grabber. That only makes sence since I used the power outage as a real possibility (10 times last year). It would really suck to have a backup stove and no way to push the air into the house. The place I'm heating is about 1,100 square feet. I would definitely want a way to close and open it so that I'm only using it during the coldest part of winter. I don't want two big holes going in and out of a colder outside room open all the time. I do plan to insulate the shed as much as possible. If I can get enough of the styrofoam blocks I'm using for the skirting I can cut them up into 4" thick chunks and use great stuff foam in between the cracks. I'll post a pic a little bit later with a steel pipe that I got from my last job. I'm hoping to use it but it may be too big. I believe its 10"x 4'. Swizzle
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Post by Donkey on Oct 29, 2009 7:39:33 GMT -8
Would the pipe be for the heat riser? Cause a 10" system would put out MAD heat!!
Seems dangerously large to me..
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Post by swizzlenutz on Oct 29, 2009 8:25:59 GMT -8
I probably won't use it for this system. I used a short piece for a small L tunnel rocket at my old place and I had flames from 3 to 4 oak branches 5 to 6 feet in the air. I'll more then likely do this one all in brick. I bought ten blocks today for the base. Its a start. Swizzle
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Post by swizzlenutz on Oct 29, 2009 9:07:29 GMT -8
I just went and measured it. It's at least 1/4" thick steel water pipe made for industrial sized sprinkler systems. Its 8-3/4's inches x 46 inches. It's also really heavy. I'd say about 80lbs. As much as I'd like to use it I think this would be better as a riser for a water heater set up with the copper coil wrapped around the pipe. How do I find the adobe bricks? I've checked lowes and homedepot and they don't have it. I'm thinking about building the base out of 4x8x16 block. I'd like to have a small feed tunnel as well as a larger firebox for those bitter cold days when I don't want to go back out every half hour to push the wood in. Another thing I was wondering about is the small chamber that holds the primary fire before it enters the burn tunnel. I saw one guy (I believe Larsmith217) loading his with little wood chunks. Why wouldn't good dry mulch or wood chips work for that? I'm just trying to think of cheap or free sources of wood. I also saw another design that had a hoop above the primary burn chamber for holding large sticks up to 4 to 5 feet in length. What's your thoughts on that? I'm just trying to think of ways to load the fire and go for an hour or two at a time before re-stoking it. I know I got a lot of thoughts. I was also thinking about another chamber in front of the riser that would be big enough to place a bigger chunk of wood. Say 6 to 8 inch blocks. This chamber I would add a bigger block and then completely seal the top. The block would rest on a grate and be in the burn tunnel about an inch. Would this extra chamber create extra drafts that would effect the flow or do you think it would work? I might even be able to use the same grate but block the hole completely with wood chips or mulch. If you can't picture it then I can draw it out. Swizzle
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Post by swizzlenutz on Oct 29, 2009 12:16:29 GMT -8
Ok after reading about wood chips being used as fuel I'm going to attempt to create a large cement box above the burn tunnel and use that to put my wood chips in. My only question now is where to find a good piece of steel grate. It has to be at least 8 inches wide so I think an 8"x8" piece would be fine. Providing I can find a piece that can take the heat. Any suggestions on where I can find a nice little bit like that? I'm thinking barbecue grill but I think the rocket stove would get a bit to hot for it. The weight of the wood chips and the heat would probably warp it pretty quick. I might even take short bits of rebar or something like that to make a small grill. Swizzle
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Post by swizzlenutz on Oct 30, 2009 11:43:28 GMT -8
I got some more brick today. So far 22 4x8x16's. Once I figure out the size of the base I plan on taking some white paint to the grass, moving the block and starting the dig. I'll probably just take off the sod layer and tamp it down good. I want it as level as possible. This one may end up being closer to 6 feet high. My one neighbor is being friendly again so I know she'll be asking me what I'm building soon. Hopefully it'll be all built and running before she gets too nosey. I do have a construction question on the riser. How much of a gap between the top of the riser and the top of the heater. In most cases its a 55 gallon drum. I'll be using all brick. Should it be the same size as the rest of the design? This is going to be a very short run unless I re-think the design a bit. Its gonna be a lot of wasted heat. Should I try to make a brick tunnel that zig zags back and forth across the 40" pad and then maybe up to a second level of zig zags before I have an exit pipe? The exit pipe might end up being all brick too. How long should I try to make the tunnel and how many zig zags is to many? The whole pad is going to be small no more then 5 feet and probably closer to 4'x4'. Right now I want to get the basic stove and pad done and then start adding mass as I go. This is going to be next to the house so I'll need a roof for falling snow. Hmmmm. I could put it where our burn pit is now but I'd have to insulate an awful lot of pipe before it comes into the house. I could probably bury it next year and get a bit more elaborate I suppose. Swizzle
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Post by Donkey on Oct 31, 2009 9:48:36 GMT -8
... Adobe brick needs to be made, you can't buy them at home depot. Takes a little effort at first and time for drying but they are VERY inexpensive (like the cost of some sand, a little straw and some dirt.) and really useful for this kind of project.
The long stick with holders thing is good theory. But in practice, I've found that long sticks will occasionally hang up in the feed, the fire will then crawl up and out or the stick will topple over. It's a fire hazard.
Wood chip fuel. I haven't played with that yet.. Seems like a good idea though. Biomass fuel pellets can be made out of just about anything. What would be nice would be some kind of passive way to feed in more pellets when they are needed. Something that doesn't use electricity.
Firepath, zig-zag.. If yer runs are short(ish) and you want to squeeze as much heat out as possible, make em go DOWN, not up. Run the heat riser to the top of the mass, then do all the zig-zaggy runs back down to the bottom and chimney out from the bottom. It'll take fewer runs and you'll get more heat out of it.
You know, there's a lot to be said for rocket bell stoves. You might want to go look at peterbergs designs. The feed box can be done several different ways (a couple right off the top of my head). That bell chamber is VERY efficient at distributing heat. It's pretty easy to build too.
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Post by swizzlenutz on Oct 31, 2009 10:28:46 GMT -8
The sand I can get for free, what about fully dried grass clippings in place of straw? The landlord's son mows all the side yards in the park and dumps the clippings where I can get to them with no trouble. The clay is the tough part. We have clay in our soil no doubt about that but a lot of it is dirt and other organics. Is there an easy way to separate the clay? The first thought that came to my mind was a class room experiment where you add soil samples to a jar of water and mix it really well. Mix it until nothing is on the bottom and its all in motion. Then when it settles you measure the different layers to determine your soil type. If I could do that on a larger scale then I could easily get pure clay but that's a lot of extra work.
I was wondering about the stick hoop and how much of a potential fire hazard it could be. I was planning on making sure the sticks they were used would be very straight and place the big end down so the branches don't hang up as much. More then likely it would still happen even on rare occasion. I think if I was to do a set-up like this it would have to be with stick 3 to 4 feet with only about a foot sticking above the hoop. Then try to use a loop that is smooth and less likely to catch the sticks.
Wood Chip Fuel: I read somewhere that if air is going over the top of your wood then you're defeating the purpose of the rocket stove. My thoughts on that statement with the wood chip burner s that the rocket stove would have to be purposed for burning wood chips. A heat resistant grate of some sorts would have to be formed into a basket that would fill the top half or 2/3rds of the burn tunnel. With the top 1/2 or 2/3rds completely blocked with wood chips the air flow underneath should be adequate enough to ignite the wood chips and as they turn to ash more would fall in place. i think I would put a solid plate at the entrance of the basket to keep the air flow underneath as tight as possible. I have my doubts a BBQ grate could handle the heat for long. I would want 1" to 1 & 1/2" mesh for the basket. The mesh size would need to be adjusted or changed depending on the size of the wood chips or mulch even. Any thoughts on this idea?
A big thanx on the downward zig zag. That does make much more sense.
I've been looking at the bell design as well. I still like the idea of a Rocket Stove Mass Heater a bit better. Probably because they are so much more common. I'm not through checking out the bells though. A lot of good info Donkey. Thanx a bunch. Swizzle
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Post by Donkey on Oct 31, 2009 20:04:17 GMT -8
You don't want pure clay. In fact, clay soil with LOTS of sand and other stuff is best.
Just get the dirt wet, make a loaf out of it and let it dry. If it crumbles, there isn't enough clay. If it cracks, there's too much. Too much clay can be fixed by adding sand, to little really can't be fixed, though your idea sounds interesting.
Ideally, your dirt loaf should be good and hard when dry, not crumbly, not cracking. That's PERFECT, as you don't need to do any works besides get it wet, add straw, mix and apply.
Grass clippings won't work (I don't think). Grass has food value, even the dry stuff, and it's fiber content is kinda low. Straw is better, though just about any fibrous material will do.
The "no air over the wood" theory is about Aprovecho style, horizontal feed tubes. With the downdraft feeders, ALL the air is coming down over (and through) the wood.
Maybe a stainless steel bowl (or restaurant food container, stainless of course) with holes drilled in it would work. You would start a fire in the bottom of the bowl and after it's going, (maybe) add chips over top. The bowl would need to fit the downdraft feed tube fairly well so all the air is forced through the chips. Some kind of shaker arrangement would be needed to shake out ashes and clear the holes. There would need to be an ash drop below to keep it from clogging, just a shallow well below the feed that can be easily cleaned.
The bell stove is a mass heater. The bell itself is built of brick, or cob, adobe, any heavy stuff. The advantage of the bell is it's excellent heat distribution, just about as even as can be.
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Post by swizzlenutz on Nov 1, 2009 6:57:20 GMT -8
Clay Bricks: Would it be best to let it dry or to try to bake it?
I think I could find fibrous materials easy enough.
I don't think you would need a shaker system if the holes were big enough. An ash pit would be a must and probably a fine(r) grate over the ash pit to catch unburnt bits and let the ash fall through. I may play with a design a little later with just the BBQ grill. I have some chimney blocks I can play with for a makeshift mulch holder. The mulch I have here now will need to be sifted. It has quite a bit of dirt mixed in with it. If I can get something going and actually working to my satisfaction then I'll take some video of it. It'll take some measuring, cutting, and bending to get the grate in the shape I want it in. I'll probably start a fire under the grate once its full of wood chips and see if that will be enough to get the whole thing going on its own.
The bell I would think would be a much better design for inside of a house as far as the heat distribution goes. Right now I'm gonna try to get some heat through a single pipe in the house. If I'm happy with the results then next year I'll be cutting the underbelly and redoing all of the duct work and maybe even figuring a way to hook up a thermostat. Right now wood chips or mulch is about $25 to $40 a ton. A lot cheaper then $249 a ton. The cheapest I've seen for pellets this year. Swizzle
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Post by Donkey on Nov 1, 2009 16:16:28 GMT -8
Just let it dry. The bricks will become somewhat fired when you use them. "Bisque", I believe is the term.
Yer probably right about the bell. Though a thermal mass can placed inside with the outer skin of the bell being insulative. The thermal mass then would be heated very evenly... In case it really matters, which it probably doesn't and adds a certain amount of unnecessary complexity.
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Post by swizzlenutz on Nov 2, 2009 11:32:40 GMT -8
I may do a test brick with the grass clippings unless I can find something a little better. Is there any good sites with info on different materials that can be used to make cob? I looked before but didn't find much. Then again I might be able to just ask a few farmers until I find a small bale of straw. I'm not sure what the difference is between hay and straw. Always thought they were the same, just a different name depending on location. I'd like to be able to use this stove for the purpose of burning other materials as well. Paper's and cardboard for free heat. Would I need to add a screen of some sort or can I actually burn cardboard for a season and clean it out in the spring? I'm pretty sure I can get cardboard by the bale.
A thermal mass inside the bell is kinda what I'm doing isn't it? A rocket stove, mass heater, surrounded by a cinder block shell? Maybe a redneck bell? Swizzle
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Post by Donkey on Nov 2, 2009 19:14:35 GMT -8
A redneck bell.. I like that If you want to burn a lot of paper, cardboard, etc, you will need to figure out a good way to clean it out. Too much paper is a HUGE problem with most rocket stoves I know. It creates lots of fine, flying ash that is normally blown down into the pipes. The stuff tends to find the most inconvenient place to pile up and plug up flow. Though It's my thought that a wide spot, perhaps off to one side of a run with a drop and a clean-out, might create a low pressure area where ash may be sucked in and allowed to settle out. I really haven't done any testing on this but it seems logical to me. |
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