Which Aluminium pipes can i use inside heat mass on a rocket mass heater

Hi,

i've read the book recently because we are planing a small house and want to integrate a rocket mass heater on it...

trying to understand the possibility of using cheap aluminium pipes inside the cob bench heat mass, i read this several times on the forum and the book...

i remember my first cooking rocket stove had an aluminum pipe (maybe one or 2 milimeters thick) melted before the end of the first meal cooking....so i'm very reluctant on it's use...but would benefit on the low cost of material (and so the possilility of a bigger bench or heating the bench and a wall)

i understand we can only use aluminium inside the heat mass, i imagine it's because the heat is more absorbed from the mass and cools down the aluminum (and the exhaust fumes) - am i right?
otherwise i could easialy understand aluminium melting or colapsing...

but what kind of aluminium tubes are we talking about?.... would love to understand it by specs and pictures

a) metal aluminum foil ventilation tube



b) Semi-rigid Aluminum Flexible hose,air duct for ventilation



c) 1.5mm wall thickness aluminium tubing



a fast online search (probably diferent from my local dealer) makes a - 1€ a meter b - 4€ a meter c - 17€ a meter

i think the a option is very fragile... would be admired if it worked... has anyone tried this kind of tubing on a cob bench?

the b option sound reasonable and i would belive it would work if someone else already triedit

the c option is almost more expensive than spiral stainless steel tubing so i would prefer steel with that kind of price...

J. Tabordiy : Possibly C, You have read 'The Book', and have experimented with the Rocket (Cook ) Stove so all we have to talk about is ''Size Maters"

Please take the time to do several practice builds laying up firebrickS level by level staggering the joints ( sometimes called a running Bond) For purposes

of Test builds you can give our brick a quick 5-second dip into Clean water shack off the excess and then dip them in a Clay slip, this should give you a

good seal brick to brick allow simple testing and then readily be knocked apart with a block of wood about brick size !

Myself and most members here at Permies.com will all pretty much recommend that you start with a 6'' system, or an 8'' system as a 4'' system
is a very tricky 1st build, a little finicky to operate and will not allow you much thermal mass to play with !

Please consider going to the Permies Toolbox at the top of this page just below the Permies Banner and above the Permies Video of the week, locate and

clickon the [My Profile} Tab and at the new page you will be helped to add information that will help your fellow members give you advice relative to your

location. Who knows, you may have near neighbors with Rocket Mass Heater And Cob experience !

Your cellphone is your handiest tool, allowing you to save a picture of every thing you do, which layouts you have tried ETC. For the Craft Big AL

thanks for the reply... my location is north-west coast of iberia peninsula, a.k.a portugal...

so my nest question related is, would any steel tube (in decent conditions - not too rusty) work? or what is there a minimum thickeness (of the wall, not the diameter) of the ducting tube?

i think we will build a 6'' or 8'' (or the equivalent on centimeters [15 to 20 cm?])

J.Tabordiy; What we would use for piping in the mass here in the U.S. is a thin wall pipe commonly called HVAC pipe in 6" or in 8". This pipe is normally used in heating and cooling systems. It will not stand up to the high heat at your manifold so , one piece of a heavier wall wood stove pipe is used to leave the transition area and then switch over to the thin wall pipe for the remainder of the horizontal run. This piping is then covered with a layer of cob that will form a clay tunnel after your thin wall pipe has rotted away. However in your case you will not be able to find this style pipe. Consider using clay bricks to form most of your horizontal run only switching to pipe when you rise up out of the mass . If your mass is thick enough you can cut a 55 gal barrel in half length wise like a bell ,and stack end to end. Of the photo's you showed us ... (A) no good ,do not use. (B) looks like automotive tube and I have never seen it as big as 6" or 8"... sealed over in cob if it is big enough could work. (C) This is more than you need and probably expensive. All you really need is a tunnel for your heat to travel thru , what you use is less important as long as it is smooth with no sharp corners , not able to be crushed by the mass above. You will want some kind of stove pipe as a chimney at the end of your mass, although a brick chimney could be built as well. The temperature leaving your mass should be apx 130 F or 55 C . Hope this helps more than it confuses Tom

J. Tabordiy : Seriously, a good place to go cheap is the horizontal ductwork in your Thermal Mass Bench, all ductwork will rust, from the moment you paint on

the clay slip- through all the wet cob, and then all the products of combustion from your wood fuel, and the 10% moisture content of that fuel when it is considered

kiln dry, for a period of weeks, as long as 3 weeks, and balanced against the Moisture content in the air, the ductwork within your Cob will be constantly wet.

This is one of the reasons we tell people the more dense stone they use in their Thermal Mass Bench the less( high moisture content ) cob they will have to make!

For this reason any ductwork should be considered a sacrificial form for creating the horizontal chimney in your thermal bench !

Here in the States we will have three grades of pipe, a heavy Wood stove black, a Medium Galvanized, and a Lightweight Galvanized Cold air return ductwork.

To that I add one more grade free! Often after house fires due to the amount of water used in fighting the fire- all the houses appliances are trashed and get

replaced, this is usually done by the general contractor long before the H.E.V.A.C. contractor shows up,you will get a mixed bag of 6'' 8'' and bigger, I have had

good success ether removing pipe from the skip or even bribing the contractor foreman with cheap beer ! Hope this helps and is timely ! Big AL

Late note : Click on the link below and scroll down to the 9th video the one labeled rocket flames Rocket mass heater barrel prep ! this is definitely in your future


http://www.richsoil.com/rocket-stove-mass-heater.jsp


Then start at the 1st video and watch them all they are a little dated so Any questions ask here ! A.L.

J Tabordiy, what's that J by the way? Jose, Joao, John?

Anyway, here in euroland, iirc, stove tubes are normalized.

Usualy 111mm 139mm and 153mm for the aluminized steel types. And the bigger ones, 180 200 220 230 250 and 300mm usualy are either painted steel or stainless steel.

I like the 153 aluminized, as it's cheap and holds well.

I managed to get cheap double wall flex type stainless in lenghs up to 2m from my supplier, which were offcuts. Somethjing like 14 or 20m for 30 euros. Just to get rid of it


But my preffered cheap method, is Matt Walker's half barrel system.

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

i think i got it.... when you talk about sacrificial forms for the cob, do you mean that if you unmount the bench 10 years later is ok if the tube is all gone?....

in the RMH book they talk a about the risk of exhaust excaping from the bench and that should not happen...

there is no way exhaust can pass through cob? just on the cracks?

J. Tabordiy wrote:there is no way exhaust can pass through cob? just on the cracks?

When the RMH is started from cold... perhaps but not likely. When you got smoke out of cracks, it will come out the feed as well. But when warm, the whole thing operates in under pressure, no doubt about that, through every crack air is sucked in. I've checked it several times and much to my surprise and despite some cracks in a bell the CO detector of the Testo didn't even flinch once. So I used the same Testo to measure at different places all over the heater and every time this equipment detected a slight vacuum.

So don't worry, the only risk you run is when there's a glowing coal bed in the feed and you close it off completely. Only shut the thing tightly when it's completely dark in there and you will be fine.