8" RMH

Hi all!
First time poster so be nice 😊
My wife and I are renovating a run down double brick home at the moment on a 20acre block.
The combustion heater was absolutely useless so we pulled it out of the old chimney and are covering over the space.

We planned to install a new combustion heater on an internal wall with an exposed flue but have decided to install a rocket heater instead!

I have read two of the books and watched everything that I can find and believe that I am ready to start planning our own.

So far I have acquired two brand new 210L oil drums for free and have found a supply of 230x110x76mm (9x4.3x3")  fire bricks for $3AUD each which is reasonable here.

Still trying to find some suitable stove pipe.

I'm having trouble understanding the floor insulation layer below the fire bricks. It is not well enough explained in either book for me.
I have also noticed that both the Ianto and Leslie book and the Erica and Ernie book use an ash pit which is no longer recommended which is fine.

The heat riser is also shown using half thickness bricks but I'm hoping to be able to use the full size brick if there is no problem with that?

Lastly, for brick layout is a little hard to decipher for me. He Ianto/Leslie book has a decent set of diagrams but I believe I Erica in one of her videos mention that she now makes a taller burn tunnel to leave room for ash!

Using that sized brick would give me 110mm + 76mm which can make the burn chamber 7.3 inches tall and making it 7 inches wide will give me 3/10" free to leave a layer of ash whilst maintaining ~50square inch cross section area to match the 8" pipe.

Benen, when it's mater to heat a house, i often advise to switch to batch. Except if you are really fond of the J tube, or want to go the extreme scavenging route.

http://batchrocket.eu/en/

Thankyou for the reply 😊
Why do you suggest the batch rocket instead? I believe I have access to a friends brick cutter so the construction would not be a problem.
My wife and I like the idea of having visibility of the flames that you lose when switching from a combustion to a RMH.
The sidewinder option looks like it would potentially fit the space that we'd like to use.

Well, to me, a batch rocket is more powerful. Needs less tending. You can see the flames. Has less smokeback. Mind you, it might consume a smidge more wood. And in my huge one, i find i deal with ashes a lot more than with a J tube. Tho, i have never had a J of this size. My workshop batch is a 220mm one. The sidewinder, i have never tried. It needs to be built properly. No deviations from the design.

I would say, i preffer this one to the sidewinder.

http://donkey32.proboards.com/post/16159/thread


In Dutch, but the pictures are self explanatory.

http://www.ecologieforum.eu/viewtopic.php?f=3&t=4610

It looks extremely complex to build in comparison to a regular rocket heater!

If i can build a normal batch rocket, it must be not that complicated.

Haha. Well our space to heat is quite large. Where did you get the plans from? I would like to try building one from old bricks outside to test.

Benen Huntley wrote:Haha. Well our space to heat is quite large. Where did you get the plans from? I would like to try building one from old bricks outside to test.

Well, no plans. I have embarked at first, when Peter was in the last stages of development. There were no plans. For my first one. Then, for the range rocket, i went along what i had. I had to fit it withing the existing shell. Then, for my workshop one, i had to go along with the parts i had scavenged over the previous months.

I draw my own plans with sketchup. But it's often hard for me to follow these. There's always a last minute adaptation to be made etc.

But it's pish easy. Once you know the way to make your core. You can fit it in pretty much anything.

Mind you, if there is no plans per se. There's measurements.

http://donkey32.proboards.com/thread/734/peterberg-batch-box-dimensions

I've spent some time this afternoon learning sketchup and started to draw out the core for a 200mm system.
What I've just discovered is that standard bricks will require an 'n' shape to be cut out of one of the bricks in the heat riser to get the correct port height. Or am I missing something?

I just realised how bad that image came out.
Also, three bricks on their sides for the box falls 11mm sort of the required 432mm height

Benen, 11mm is nothing.

When i do the port, i use full bricks or cut bricks for the sides, and a brick across on top if possible.

Have you seen this http://batchrocket.eu/images/rockets/files/BrickSidewinder.skp

That 11 mm is just 2.5% of the port's height. Ignore it, it's well below the tolerance of say, 5%. In case you feel unsure about it, compensate for this in the width of the port, but again the difference is absolutely minor.

Thankyou both. You've been so helpful. I will continue playing with sketchup layouts for the 200mm size.
I did notice that it appears that using 230x115x76 bricks takes up almost the entire interior of a 55gallon drum for the heat rises.

Do you still feed the exhaust through a bench before exiting the building?

The octagon riser looks like it would be very difficult to build precisely?
I calculated around 80-81mm for each of the 8 sides to get the correct cross sectional area.
Is it really that much better?

If you have 3" thick bricks and a square heat riser, I would be unsurprised if you ran out of space between riser and barrel. In that case, I think the octagon would be not only more efficient but fit better in the barrel. If you are using hard (ordinary) firebrick, you do need to insulate around them for the riser, which will add an inch or two to the thickness on all sides.

The 3" hard bricks will have significant mass which will take longer to heat up and get to a really efficient burn. Thinner bricks or other ways of getting a lightweight riser would be beneficial.

Yeah that makes great sense. I can get bricks much thinner but they are $6 each instead of $3!

Maybe I can split 3" bricks down the length with a brick saw.

Benen, forget about that! It will take you a lifetime.

Keep the firebricks for the box. Buy some ready made castable refractory.  Usually runs in the 25€ per bag, in euroland. You would need two bags iirc, for a full 8 inch core.

Ah really? How did you go about casting the core? I've never done anything like this.

Benen Huntley wrote:Ah really? How did you go about casting the core? I've never done anything like this.

Sorry, me neither. I think Peter has good explanations on his website.

Myself, i just go to italy, and buy pizza oven slabs, and chimney refractory tubes. Pish easy i would say!

Haha. Well that's not fair!

Argh! I just read that the internal surface area of the bell needs to be 9.4m2! My barrels are about 1.77 each only. I can't stack 5 or 6 barrels end on end in my living room!

Maybe I should be looking at 6" instead. I just assumed 8" because that is what I have been looking at with j-tube options.

Benen,  usually,  you replace a eight inch j by a six inch batch. For equal power.

And most of  the bells are made out of mass, not metal. Métal, as in the barrel, is a direct heat radiator.  If you have top much metal radiator, you will overheat the house before you warm the mass.


Check this,  
http://s65.photobucket.com/albums/h228/mremine/NYC%20Rocket%20Stove%20Build/

It could of some interest.

Ah is that right? I feel like I'm learning so quickly but missing huge chunks of important information!
That's a lot of fire neighs to build a bell!

Well, i i understood correctly, you said that's a lot of firebricks to build a bell.

Not necessarily. Here's how i built my workshop one.

http://donkey32.proboards.com/post/19233/thread

This might give you ideas.

Impressive. I looks enormous!

I think one or two guys have donne bigger. It's a 220mm, with 4 tons mass.

Not something I can fit in my house haha.

Well here's where we are at. I've done a quick mock up of the house living area and a couple of heaters. The one sitting in place is a sidewinder option win a bricked up bell. Internal surface area is 5.7 square meters excluding the floor.

A couple of remarks:
It looks like a 6" version, judged by the size of the riser. If it is, then the ceiling of the firebox is too high, that would influence the workings of this design quite a bit.
The ceiling of the firebox is done with bricks on edge, introducing too much material, coming up to working temperature will be unnecessary long this way.
The exhaust pipe is far too small, it appears to be a 4.5" diameter pipe. This should be 6"as well, plus in order to avoid stream problems, it should be at least half the diameter of the pipe from the floor and the corner, preferably more.
The top deck of the bell and the walls above the riser should have a liner of refractory material, split firebricks would be sufficient.
The ISA of 5.7 m² is a tad too much, you should expect problems starting cold. And it will be a drama getting the thing dry.

Hi Peter. Thank you for the prompt reply!
I have changed the top of the box to be a 30mm thick piece of material. Refractory concrete with reinforcement bar perhaps?
The box is 21mm higher than your specification due to the wish to use full bricks. The port is also 8mm shorter for the same reason.
Are you saying this will be a problem?
I will post an updated version 😊

Is this getting closer?

Oh I forgot to mention! I have the ISA almost 5.4m2 by making the bell 1/2 brick narrower along the longer side.

OK, this is much closer now.
The whole of the thing is within tolerances, so no  new problems here. Please leave out rebar in hot refractories, the steel will expand faster, cracking the refractory.
The p-channel as drawn won't work, I'm afraid. It would be much better when you switch to floor channel, it looks complicated but that isn't really the case.
And you are aware of the fact that an octagon riser is much better aerodynamically? More complicated to build, I admit that.

Ah I see. I think I can do the octagon riser. Cutting isn't a problem but working out how it is connected to the box might be. OK have a play tonight.
Why won't the pchannel work as is? Air too hot if it is passing through the bell?

Benen Huntley wrote:Why won't the pchannel work as is? Air too hot if it is passing through the bell?

A p-channel should be situated right above the port with a small overhang. Yours is against the back wall in the drawing, beside the port. The secundary air should be fed in front and above the port itself where the lowest pressure area begins, not somewhere in the firebox, even the general vicinity of the port won't do.

This is a very tight design, I have to stress that again and again. The whole of it looks deceptively simple to build so people tend to think its workings are also simple. But you'd better believe me when I say it isn't, far from that. It took me a couple of years to even understand what laws of physics are in play and how.

The p-channel passing through the bell isn't a disadvantage, rather the other way around. See my three barrel workshop heater, that's more or less the same setup. The main reasons for me to recommend a floor channel is because it is easily replacable and it works really excellent.