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Building Rocket Stove / Heater for Small Trailer Conversion  RSS feed

 
Dan Cooper
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Hi All, First post. I am in the process of changing my lifestyle from 9-5 Computer Guy, to going on the road to look for my homestead. I am planning the conversion of a 16' x 7' trailer to be my home for a few months maybe a bit longer. I want to build it as self sufficient as possible and learn as much as possible about sustainable living in the process. First Project. rocket stove/Heater. I would appreciate any feed back on my plan. I wanted to make a smaller rocket stove than the usual 55 Gallon or even 25 Gallon.

Using an up turned Cooking Pot as the Heat Riser outer Barrel.
The feed and Burn chamber will be made of Rectangular 1/8" steel or aluminum same as the Exhaust chamber.
The Inner Heat Riser will also be made of 1/8" Steel Circular Tube. With an vermiculite insulation section.
There will be firebricks around the feed, burn and exhaust chamber too.


Anyway take a look at my plan and break down if you feel like it. Many Thanks.
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Plan / Dimensions
 
Glenn Herbert
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Location: Upstate NY, zone 5
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The heat riser is nowhere near tall enough in proportion to the burn tunnel and feed tube. As the standard recommendation is to keep the same system cross section, the riser so much bigger than burn tunnel may be a problem. I don't think the proposed design would work even tolerably well.

You are proposing a truly tiny unit, and the design does not scale down the way you might think. First, a 3" system is not 1/2 of a 6" system, it is 1/4 of the size in terms of area for combustion, and there are surface effects which reduce the effective flow area that do not scale down. Thus, subtracting say 1/2" from all surfaces for friction/drag effects (purely an example, not proven quantities), you have a 5" diameter compared to a 2" diameter, or 19+ square inches vs. 3+ square inches. Given the low insulation values of most trailers, you probably want more than 1/6 of the heat you could get from a 6" system.

I would suggest at least a 4" system, with the caution that a system even that small is considered very tricky to get right. You would probably want to use longer lengths proportional to a large system, as wood flames take a certain amount of time in the hot part of the combustion zone to finish burning, and a small system scaled directly would have less dwell time and poorer combustion. I would keep the burn tunnel as short as you can make it and maintain functional access, with the feed tube 1/4 of the heat riser height. This should maximize the positive chimney effect. For a minimal compact 4" system, I would try a 9" feed tube, about 14" burn tunnel, and 36" heat riser (all measured at the outer edges). A taller riser is not going to detract from the space, as you can't use the space directly above it anyway.

I would try a 2" insulation jacket around the riser (8" o.d.), a minimum 1" air space all around (airflow will be slower in this zone so the surface effects will be lessened), and a minimum 10" diameter "barrel". Given the space constraints, I think putting some thermal mass on the barrel sides would reduce the hot surface danger while still allowing radiation. Maybe split firebrick (4 1/2 x 9 x 1 1/4" thick) bedded in cob around the barrel and wired/banded in place would work.

A small system is more susceptible than a large one to surface conduction and radiation losses, and I think metal, even aside from the fact that it will have a short lifespan in the combustion zone of a well-functioning RMH, would rob more heat than you want. Weight is also a consideration for a trailer. You want everything but the mass to be as light as possible. Water heat storage is desirable but can be dangerous, so I wouldn't try that unless you have an engineering background and understand the safety factors thoroughly. I would suggest a castable insulating refractory combustion core, cast inside a metal box for rigidity in traveling. The small quantity needed for a system this size shouldn't be too expensive, probably one bag at around $50. Make an inner form of thin wood that can burn out, and the casting process shouldn't be too hard.

Lots more can be said. What are your thoughts at this point?
 
Fred Hayes
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This is about the same thing I'm doing. And I honestly have no idea what you meant on that reply. Not toale myself seem stupid but could you dumb it down for me?
 
Dan Cooper
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Well, the term 'back to the drawing board' certainly fits here. Thanks so much for the thorough reply, and for explaining my false assumptions. I will re-read, explore digest and rethink.
 
Douglas Pohl
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Here is a spreadsheet with dimensions - EZ - http://donkey32.proboards.com/thread/734/peterberg-batch-box-dimensions
 
Greg Harvey
Posts: 28
Location: Columbia, Missouri
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I posted a request in the innovators wish list for a tiny home model. Someone else already had posted some ideas for that already. What I'm wanting is a batch type with a glass door that sits outside the trailer so you could sit and watch the fire most of the year and not take up precious inside space. Next, it could be used to cook on top of the barrel, maybe with a Webber grill modification. That's two uses. It could also heat a tank of water and have a copper coil going through it for heating your hot water needs year round. That's #3. The unpressurized tank of water could then be used for radiant sub-floor heating with only one pump. That's use #4. If you want a hot tub you could also use that hot water for that too and not have the heater right in the water with you. That's use #5.

The mass in this would be the water and empty tanks will not be that heavy when you need to move. The tanks could also be disconnected from the rocket stove as well to make it more manageable to move in two pieces.

I think the whole shebang could be outside your front door under a porch roof so you could enjoy your fire making/water heating even if it rains or snows.

What do you think?

Greg
 
Douglas Pohl
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If you can imagine it you can have plans made and build it... http://tiny-project.com/

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http://tiny-project.com
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