Yet another RMH? Not really.

Dear ladies and gents of permies,

I am from India. And I have been looking up RMH build processes etc for some while now.
My resources have been;
The famous Peter Berg's site and posts on permies and donkey
The scots or was it welshman Mr Loz harrop
Most other videos about this subject have been nearly useless and so also the posts.

Let me give you a background about my understanding on the subject:-
•Best RMH diy-able involves a firebox connected to a bell by means of an L tube. And the exhaust exitong from the bell bottom. Also the air intake, exhaust exit and riser cross sections should be of comparable dimensions "performance" wise.
•Firebox needs to be made of refractory stuff or it will rot from heat. A pre-heated air supply would create hotter burn.
•Cheapest and easiest way to build fire tube and riser would be using ceramic fiber board.
•Bell can be a used oil drum, but would need some shielding using ceramic fiber paper or some such thin insulation to protect the top part of barrel from heat and resultant rot (corrosion).
•Exhaust needs to have as fewest turns kinks as possible to maintain proper uniformish draw. So even if there are turns should be executed earlier on and maximum straight path given to the last segment to provide the best draw possible.

Now my situation isn't that great, it's India!!! Every piece of scrap is as valuable as New stuff. Labour is expensive and tools hard to come by. Refractory etc is exotic stuff I'm told. Besides we don't have a culture of doing stuff like this. Last year nearly killed my self burning bituminous coal in a sheet metal square cylinder I managed to beat out of a 0.5 meter by 0.5 meter piece of steel sheet managed to pilfer from my hospital.   ;P

So my first choice will always be saving munnnny.
Btw 1USD is like 70 INR (Rupees).
I'm putting cost of material.
Mild steel- 45-55 rupees per kilo
Fire brick IS8 - 25 INR per piece
Ceramic Fiber brick ICFB9 - 22 INR per piece
Whyt Heat A castable refractory- 80 INR per kilo
Basic ramming mass - 60 INR per kilo
Acidic ramming mass- 10 INR per kilo
Ceramic fiber board- 1 meter X 0.5 meter X 2.5mm- 700 INR per piece.

Shipping could be cheap if I manage to haul it myself on some public transport .

My plan is to build something like Mr Loz Harrop (ppotty).
One tall steel box acting as bell. One small box acting as firebox. Big box would be 1 meter high and 0.5 meter square section. Small box would be cube 0.5 meter. Each made with either 3mm or 5mm MS sheet

Firebox would have gaps on sides and actual firebox made of refractory. Please recommend what to use, I'm leery of experimenting due to high costs involved.
My major issue is that almost everyone said their thingies failed when made of perlite + refractory castable. I don't know what to do.
Should I use firebricks sliced legthwise and then make some plaster type mix with whytheat + zircon sand or perlite or something else. I don't want it splitting and falling apart after 2-3 uses.

Now should I instead opt for a oil drum as bell and a non metal completely made only of firebrick lined inside with some recommended plastered refractory material that is held in a sort of cage made of Angle iron like a frame.

For fire tube and riser I'm inclined towards Mr Berg's design where he uses a slit to create the turbulence by suction, and for that I plan to use Ceramic fiber board of 1200°C rating.

Oh oh I could manage to score used motor oil, and I plan to use wood primarily but can supplmemt the wood like every 10 minutes with some pulverized coal (from handling transport etc) of which I have half a sack remaining which I have left over from my debacle last year. So I plan to use a squirter to squirt some oil every few minutes or so. Just because I can get that used motor oil for cheap, although used oil is big business here. Also thinking to use cut up tyres, not primarily only as a garnishing.

I would be highly obliged if some of the experts on board share their experience or recommendations. I would be very thankful.

Especially about the firebox!!! Oh and should I make some thin liquidy runny solution from whytheat castable to coat the fire tube and riser made of ceramic fiber board?

My humble regards
NK

Hello Neelesh and welcome to the Rocket Mass Heater forum.
From your description, its sounds like you have never built a rocket stove before. If so, I would highly recommend building one outside on a non flammable surface and experimenting with its basic operation. You can make one straight from clay or regular brick to start with. Don't worry about adding any heat storage, barrel, or other gizmos until you get a good feel of it. It can be made from scrounged materials and constructed in an hour. What you learn will be very valuable information and will lead you in the next direction from your own experience. Take pictures and post them so that we can help you out and give feedback. Hope this helps..... :)

Ceramic fiber board is the latest and most efficient material for building heat risers and other parts of the hot core, but as you noted it is very expensive, not the cheapest method. Perlite-clay, if mixed to the most insulating ratio (little clay), is weak but will work fine as a heat riser if contained in a sheetmetal outer shell. It is probably too weak for use in parts of the firebox that can be reached while feeding or cleaning. Firebrick, and especially insulating firebrick, is an excellent material for building the combustion core. Use the strongest material at the feed tube where wood can scrape it, and possibly for the near parts of the burn tunnel if you may be handling it roughly.  What works for a person who places wood gently in the feed may not work for someone who throws logs in.

You do not need any metal at all to build a good RMH, aside from the P-channel for a J-tube or the floor channel for a batch box. If old barrels are expensive but common bricks are cheap, you can build a brick box instead of the barrel.

What part of India do you live in? The degree of cold, and how long it lasts, makes a big difference in what will work best.

I agree with Gerry, build a J-tube outside and see it burn to get a good idea of how it works, before you try to design a system for your house. The J-tube is simple to build and has only a few important dimensions and rules, while a batch box as Peter van den Berg describes must be built precisely according to plan and is more technical. They are both around the same efficiency; a batch box holds more wood at a time and needs to be fed less often. You cannot open a batch box in the middle of a burn and toss in a few bits of fuel, you load it completely at the start and let it burn down. A J-tube can be fed with bits of varied fuel as desired.