Working backwards

Hi everyone,

I've been admiring rocket stoves for some time now and would like to build one to heat water for my small dairy.

The reason I named this post working backwards is because I have owned an old cast iron wood chip water heater for years and want to get it going.
From what I've read the dimensions of the intake, burn chamber and riser are all important in making it work.
I'd like to use the heater as the the riser and need some advise on whether this is practical and then what dimensions other sections should be.

Think of the heater as a cast iron water jacket tube, originally the fire was burnt in the centre and flued straight out.

The burn chamber dimensions are 240mm internally at the bottom with a very slight taper reducing to 220mm at the top with a height of 240mm, this is the proposed riser (I can add more height by mounting a small barrel sitting on top if need be)

Are these dimensions too big for it to work? If not, what intake, burn chamber, barrel (I have a 44G drum on hand for the outer) and flue is recommended?

I'd be very grateful for any guidance...

Cheers
Chris

Chris Cansdale wrote: (I have a 44G drum on hand for the outer

Cheers
Chris

Just a clarification since you haven't any location listed, Are you outside the US and talking Imperial gallons? What we call a 44 gallon drum the Yanks I know call a 55 gallon drum. Something to do with the early Yankees missing a few fluid ounces when first standardising their pints and quarts. 3.8L per Gal vs 4.5L per Gal

Are you thinking of using the water jacketed part as the riser? It sounds like the original unit had water immediately surrounding the fire chamber, which would effectively heat water but cool the chamber walls. A rocket mass heater requires a highly insulated, extremely hot combustion chamber including riser, and then puts its heat through a mass to be absorbed.

220/240 mm is close to 10" diameter, which is a very powerful system. The typical house heater is 8", and I haven't actually heard of someone building a bigger one. So the question here is, how much water do you want to heat, and by how much?


The burn chamber is only 240mm high? This sounds not like a part of the combustion core at all, but something you would mount above the riser so hot gases could go all around it, perhaps fitted inside the top of a barrel.

Yes, I'm outside the US in Australia so imperial gallons.

The heater can sit wherever I like really. I just figured it would be easy to have this as the base of the riser, immediately after the burn chamber. The original heater only has a 240mm high burn chamber, a plate sat on top and it had the original flue drawing off that. This is why I said I can build on top of the original unit to increase the overall height.

I need up to 200l of hot water at it needs to be at about 90 degrees c.

The short answer is that you can't use this water jacket element as part of the combustion core and have good combustion efficiency. It will suck heat out of the fire and make it smoke.

You can use it above or after the combustion zone where there is only hot exhaust to handle.

Thanks Glen,
so the top of the riser would be ok?

Yes, above the top of the riser should be okay (not as part of the riser).