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Rocket stove - riser using fire brick questions

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Hi all,

This is Michael from Sydney.
I am new to this forum. Nice to meet you all.
I have built a cooking rocket stove using a 20L oil can and insulated it with vermiculite mixed with concrete in 4:1.
The burning chamber is another tin can. I attached a picture
It served well for the last 2 years. It has been very rocket. (I used it less than 10 times a year, mainly for BBQ using fuel of garden waste, twigs and small branches)
But, tin burning chamber is not durable. It started rusted off and the insulated layer exposed and fell bit by bit every time I use it.
I decide to build another more durable one using fire bricks as the heat riser.
Although Sydney is not very cold in winter, I would like to extend it to an outdoor mass heater still.
Basically, my idea is using a removable cast iron BBQ hot plate. The hot plate can be used for plate cooking. Or, I can replace it with grate if I want charcoal BBQ.
If hot plate is used, most hot air will be forced to go thru down the exhaust pipe and warm up a bench and then to a chimney.
So the hot plate need to be relatively fit to the openings.
Please give me some comments on this idea.
I am not very handy. I need to think it thorough before start.
And I will build it by phrase.
If the above idea does not work, I will still build one for cooking.

I have a few general questions.
1. When using fire bricks for the heat riser, should I use refractory cement?
2. I have heard that the heat riser must be insulated as well. If so, I plan to mix refractory cement with vermiculite in 1:6 and apply about 3cm on the heat riser more less like render. Am I correct? (I planned to do a 4" [10cm] system only )
3. As a J-shape heater riser is quite enclosed, how do I clear the ashes? I mean, how to design my riser/heater being easy to clean up ashes? For a J-shape, I can only think of mounting a small front metal door. But it could be dangerous as someone might touch on it and it is close to the burning chamber. Can some one shed me some light?
4. Do 38% alumina content fire bricks good enough? There are 38% and 45% available in Sydney I have found.

Michael Cheung

[Thumbnail for 10423969_10152078178312714_1712302047686196983_n.jpg]
Rocket Scientist
Posts: 3958
Location: Upstate NY, zone 5
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1) Yes, you should use refractory cement.

2) 3cm will probably be adequate for your modest use. More would be better, but don't worry about it. For a home heating application you would want more insulation. Use the firebricks on edge so you get the thinnest wall you can; this will minimize expense as well as the amount of mass you have to heat up.

3) For a 4" system outdoors, I think the easiest method would be to put in a brick at the bottom end of the feed tube that is just loose enough to slide out for cleaning access. As long as the joints are small, you should not have problems with air leakage.
Posts: 86
Location: Northeast - 5B
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i wont comment on the particulars ... ill leave that to Glenn and others as I am a noob.

I am interested in what you got cooking on the grill.
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