Having read so much on here, I wanted to actually share my own experience. I'm prepared to be told I don't have a rocket stove, and i've probably done lots of things wrong, but I'm pretty pleased with my results and learnt a lot on the way so wanted to share in my first ever post.
So i stumbled upon the design of my water heater by using what i had around me. I had made a patio chiminea years ago based on a 13kg gas bottle and lorry exhaust for a basic chimney. This was stolen, so i made another, but wanted to extract more heat, so I essentially split a large 45kg bottle in half, and put a 13kg bottle chiminea inside it with vermiculite and cement insulation between the bottles and on the riser, then put the 45kg bottle back together hey presto i had a device that could heat the bottle and radiate much more heat out. The air inlets are swirled to try and create some turbulance inside the burn chamber. (didn't really work TBH)
Then came my water heating requirements based on heating an above ground swimming pool.
So i decided the throw a 110litre open drum over the top of the heater i had built and then fabricate up a basic exhaust, back out past the drum. See evolution picture below (hopefully)
I wish i could get a thermosyphon going, but this arrangement would be tricky with the height of the pool at ground level and trying to get heat extraction after burn chamber in a small foot print.
This thing burns hot! the central steel bottle, glows red, and so long as I don't block the air inlets with wood it burns without any smoke. It burns so hot that after two summers of use the central steel bottle has collapsed and the heat riser is now showing through the door (sad face). I'm amazed anyone could build a RMH with steel burn chamber and it last any length of time. I'm amazed the amount of pool heaters you see people throwing copper coils into a woodburning stove - this must be so smokey and inefficient as the temperature i guess does not got nearly as hot as a well insulated burn chamber, that is aloud to burn hot.
Now some questions/discussion, having seen the potential of this kind of combustion and heat exchange system, i want to do it properly. So I'm thinking i need to build a fire brick burn chamber - is this necessary or is there experience of steel combustion chambers with something i am missing?
I don't want to have to baby sit a J tube style and like to be able to chuck good sized logs, i guess you'd call this a 'batch box' style?
Something my system does not have is a horizontal burn area, just a steel door i open and close
I'd like the idea of a vortex - and it looks like this can be acheived with some simple plates inside riser, - is there good advantage in this?
Any other thoughts?
Even if no one replies, I hope this encourages someone to build their own attempts at efficient burning, even if they dont get to RMH levels, you'll learn a lot.
Hi Neil; Welcome to Permies!
Well you learned a basic truth about rocket stoves.... Metal can and does work but ultimately is doomed to fail.
A batch box stove properly built will scare you with how hot they can get.
I just built my first bb recently. In five test burns it completely destroyed insulated firebricks! They were rated for 1750 + F continuous....
The new version has 2700 F hard firebrick and it seems to hold up.
Ceramic fiber board and ceramic fiber blanket are the newest innovations in rocket building.
The five and six minute risers are super easy to make.
Heating water with a rmh can be safely accomplished. Just keep an open (non pressurized)system.
Steam can seriously hurt a guy when it feels trapped, and wants some space....
excellent, thanks for the pointers. I'm happy i can construct a decent burn and feed chamber - just need to research the type of mortar/brick, however i'd really like to use my existing heat exchanger, which is quite simply the gas bottle welded to the 45 gallon drum. That doesn't leave me much 'thickness' for a riser - when my bell chamber(?) is only 315mm wide, i wouldn't be able to construct the riser from brick and fit it in the 315mm bottle for a bell I don't think. I did look at a chimney pot for a riser (any experience of this?), but not sure how long that would last in the heat? My existing build had approx 5" inner steel tube, vermiculite/cement mix 8" outer tube, not sure what sort of temperatures I should design for in the riser.
I understand a conventional bell would be larger, perhaps with piping coiled in it, but that feels quiet expensive difficult to make and very easy to get a boil in the pipework. My system worked, i just need some unobtanium to make it from!
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