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Rocket mass heater with "old" cast-iron wood stove

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I don't remember where I once read that the burn tunnel was one of the first parts of a RMH that had to be replaced. And, since people give away cast-iron woodstoves for free where I live, I decided on this design. It will eventually be on the inside of a polytunnel facing west. I intend to use it mainly in early spring to protect/grow seedlings and late autumn on nights where we expect frost. Apart from that I will probably just use it when I need to heat the polytunnel to work there.

My plans are as follows. To dig a small trench and make a French drain under the bench, since the bench is at the bottom of a sloping hill (facing west.). Then I will fill with stones and gravel, to separate the bench from the soil. I will dig holes to plant tomatoes behind the bench, and make a small stone path in front of the bench.

I want to insulate the rising pipe, that will be on the outside of the polytunnel (approximately one meter away from the wall) and make a small fireplace so I can heat this chimney before I light the stove on the inside - especially in winter. The stove, even as it is now, is not that hard to light, since the cast-iron wood stove have an extra opening in the middle of the burn tunnel - makes it easy to clean as well.

There are many issues with this design. When I have a strong draft due to wind, the oven burns very well. But, on days with no wind, although I have a strong enough draft to keep a satisfactory burn, I'm not getting the strong burns I want. That's also part of the reason I want to insulate the rising chimney, and probably as much of the cast-iron oven as possible. I assume that insulating the exhaust pipe with a bench will also help the draft.

Any inputs are very much appreciated.

best regards

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Should I insulate the rest of the cast-iron stove with cob?
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Posts: 3124
Location: Upstate NY, zone 5
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You say you have used a cast iron woodstove for the burn tunnel... what kind of liner or insulation do you have? What are the internal dimensions - width, height, length of the burn tunnel, and of the feed tube and heat riser? Those all need to be in proportion for the combustion to work optimally.
Oystein Tandberg
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I don't have the exact measurements; the cast-iron stove is insulated on the inside though. The gap between the pipe and barrel is about 5 cm.
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Posts: 4154
Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
hugelkultur fungi books wofati solar woodworking
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Oystein tandberg : Please tell me if i and seeing correctly what I think I am seeing in you pictures !

You have lain a conventional old wood/coal stove over onto its back and now from left to right the ash pit door is on top, in the middle is what originally

the door for access to the Shaker and Grates; And what would have originally have been the original wood feed door is completely covered by the Cob

Structure you created to be the Heat Riser !?!

This is at least as different an application of using what you have on hand, - However You are still very much in danger of your success, as being able

to generate the high temperatures that a working rocket can create requires a great deal of insulation to protect Your Combustion Core*, and the outside

of your Heat Riser needs to be insulated to increase its efficiencies !

Please , more pictures! Like glenn i want to hear/see more of this build !!! For the Good of the Craft ! Big AL

For more information on the rapid destruction of un-insulated iron and steel in the area of the Combustion Core you can do a google search for " High -

Temperature Hydrogen Attack !

O.K., You posted some more pictures while I was Typing ! Again very interesting use of the materials you have on hand - It would be nice if you could

borrow a Pyro-meter and get a series of temperatures off of the surface of your Wood/ Rocket Hybrid ! A.L.

Oystein Tandberg
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Here is a link to one of the test-burns -
There will be plenty of time to discuss your objections when and if you return. The cargo is this tiny ad:
Greenhouse of the Future ebook - now free for a while
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