I am new to the batchbox and would like to build an 200mm system with two bells, one inside the house and one outside. Connection of both will be done through a 300mm hole in the wall. A 200mm Pipe surrounded with 50mm ceramic fibre blanket insulation will go through that hole. The wall is a strawbale lime plastered wall. This is why I am using 50mm thick fibre blanket insulation.
The back of both bells will be against the wall with a 50mm ceramic fibre blanket in between.
I have built the box out of 50mm ceramic fibre boards. The box will be lined inside (bottom, left and right) with 25mm fire bricks and the internal dimensions of the box will match that of an 200mm system as specified by Peter.
The heat riser will be octagonal and also built out of 50mm ceramic fibre boards. This will seat on 75mm of ceramic fibre board so as to be in line with the inside of the fire box.
The bells will be built out of clay bricks, 230mmx115mmx75mm (from a dismantled chimney), not firebricks as they will not be in direct contact with the fire.
Questions I have:
- What can I use to cap the top of the inside barrel? I was thinking about using 6mm steel plate to have immediate heat release.
- The bottom of the box will be 150mm from the floor seating on a steel frame. The top of the heat riser will be at 1665mm (150+50+25+1440). With the bell being 2200mm high, that will give me a 535mm clearance to the top of the steel plate. That way I hope to avoid having the steel plate exposed to too higher temperatures. Does that make sense or should I raise the bottom of the box by 235mm to have 300mm between the top of the heat riser and the steel plate cap?
- What temperatures can I expect at the transition between the two bells and will the 50mm fibre blanket around the pipe connecting both bells and between the back wall of the bell and the house wall be enough not to affect the straw bale wall? The straw bale wall and the wall penetration have a 30mm lime plaster on top of it.
- The floor is a concrete floor with ceramic tiles. Do I need to add an insulation layer on the floor or will the temperature be low enough as to not affect the tiles and the concrete below?
- I will be adding a clean out opening at the bottom right back of the inside bell and bottom right of the structure supporting the chimney. Is that enough?
Inside bell: width=970mm, height=2200mm, depth=590mm. ISA = 7.4sqm
Outside bell: width=670mm, height=600mm, depth=370mm. ISA = 1.5sqm
I have already got suggestion regarding adding a bypass hole up in the first bell directly into the chimney to avoid problems with cold starts.
But instead of a second hole in the wall I would rather just use the clean out opening near the chimney bottom to get the draw started by burning a piece of paper there? I have been advised that this could not work very well.
The big bell is in the living room. The small bell is in an enclosed outside area. We could call it greenhouse as well
I was looking to get enough heat so that we can seat outside comfortably in the winter. It does not get really cold here (Kerikeri, NZ) in the winter at night, lowest is around 6deg celcius outside at night. During the day around 14 deg celcius. But I guess because of the greenhouse effect and the massive outside lime plastered wall that is heated the day, we should get around 12deg celcius inside the greenhouse at night without heating.
I am happy if we can get this up to 18 deg celcius with the second bell.
The room is about 30sqm in total.
Here is videos of my first burn:
I haven't run it with full load yet.
I intend to run some more tests to make sure that the firebox and heat riser are all air tight.
What should I look for to ensure that the whole system is properly working? I do not have all the tests instruments that Peter has.
Will it be enough to measure how hot it gets at the top of the heat riser?
I know those are lots of questions, so please feel free to answer even it is only one question.
Hi Nono; Welcome to permies!
Very nice looking build you have there!
I have built several J tubes but have not built a batch box as of yet. I will try to answer a few of your questions. All are just my opinion.
#1) I would increase your top gap to at least 300 mm, possibly more as it gets very hot under that riser.
#2) a 2"(50 mm) thick ceramic fiber blanket should provide plenty of protection for your bale wall....
#3)I would think your floor would, with ceramic tile and concrete would be fine. Although under your core could get over heated, was your batch box bottom ceramic fiber board ?
That is all I can try to answer for you Nono, perhaps an experienced batch box builder may have better answers for you.
Not all who wander are lost... J.R.R. Tolkien
posted 1 week ago
Thanks thomas rubino!
#1) The top gap is planed to be 535mm from the heat riser. So that would align with what you've suggested. In addition I think I will fix around 25mm of ceramic fibre blanket on the steel plate cap in the area just above the heat riser, maybe 400mmx400mm to minimize heat impact on the steel plate.
#3) Yes the batchbox bottom is also 50mm ceramic fibre board as on the picture below. In addition the firebox will be 160mm away from the floor on a steel stand
I will update with pictures and videos as I make progress.
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