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.
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.
posted 4 years ago
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.