New Mass Heater (my first)

Hi, I originally wanted to make something portable, but then the idea evolved into a mass heater. I have a hybrid design in part inspired by one of your members. Here is the construction (kind of a long video, just jump ahead if it gets to long in the tooth)

http://youtu.be/jLR8cAz1hTA?list=PL3AD33C058355581E

I made essentially a cast core that also routes the heat exhaust to my flue. I did my first burn yesterday and the sides of the cast core didn't even get warm! The flue got hotter than I really wanted and I have a couple of questions. First some details (as I remember them)

6" system
Feed tube depth (to bottom of channel) 10" + 4" of flue liner on top of core
Horizontal measure of channel from front wall to back wall 15-16"
Bottom of channel to top of heat riser 35.5"
Current gap between top of heat riser to inside of barrel top - 1.0"
Barrel 17 gallons (I think)
Flue is 6" diameter
Horizontal run of flue is about 11-12'
Vertical run of flue is roughly 17'

I'm still waiting for my infrared thermometer to arrive so if you want temps I should have them soon.

I plan to seal the drum with cob, but I think 1.0" gap is too small and was thinking 1.5-2.0" would be better?
I have some patio blocks surrounding, but not touching my horizontal run of flue, would packing in cob lower the output temp?
I think I may be getting too much ash, and it contained charcoal. Should it?

Love your information. I have read many threads here and done months of research before starting. Thanks for the help already even though this is my first post!

Bill Rust : Welcome to Permies.com/Richsoil.com and A Big Welcome to the Rocket and Wood stoves Forum/Threads, With 28,000 Fellow Members World Wide
you can come here 24 / 7 and talk to someone who wants to talk about what you want to talk about !

There are many places outside of North America where the primary type of cement is not a Portland Cement based product, many of them can easily withstand the
extreme High Temperatures found within the combustion core! Portland cement will not, its physical bonds will be shattered and the Combustion core and especially
the heat riser with 40% cement is doomed !

There is no problem with creating a heat riser with a clay slip and Perlite mix, however in the burn tunnel we would prefer a little more durability and the much more
Refactory nature of Good Fire brick ! This part of your system would work up to its failure point but it will only perform as well as 50 year old models and we have
evolved past that point !

Your exhaust gas collecting arc needs to be at lest 1''thicker and a nearly perfect circle not a tiny arc, that part needs to extend from inside edge to inside edge and
down to a point well below your planned fitting for the transitional area where the gases should be collected not by a box with right angles but with the open
sweeping curves of a Trumpets mouth or bell!

I would say that unless you were specifically planing on using the top of your drum as a cooking surface, then you should go with a 2'' gap, a 1.5'' gap should give you
a spot in the center of the top that glows red hot, I doubt a 1'' gap will work at all !

Yes you want to Pack your horizontal pipe with Cob, this will lower the temperature the heat will be re-radiated at, and do it much more slowly, keeping your work
area warmer longer !

This has come across as much more negative sounding than was my intent, you obviously have many of the skill sets required for Building Rocket Mass Heaters RMHs
and you have already taught your self most of the skills needed for working with Clay !

Its interesting that you say the fire burns sideways, and the flue is too hot (exactly where) but that you have a lot of ash and any charcoal left over, a sign your draft is
not all it could be !

I am positive that there is a Trouble free Rocket Mass Heater RMH in your future, This is where I recommend that you go to Rocketstoves.com to pick up your
PDF Copy of the brand new 3rd Edition of Rocket Mass Heaters, Truly It would have saved you nearly the whole cost of your materials to date, and time and
frustration. For the good of the craft ! Big AL !

Hello Bill...welcome to Permies.com

I am sorry for also sounding like such a downer...but...I have to really second 99.9% of Al's points.

I have seen these "claims" of "home made refractory concrete" with OPC and vermiculite so many times now I want to just scream...Folks keep perpetuating this "internet myth formula" and the truth is...it isn't anything like a true refractory nor should be used in its place.

I would also point out that we really try to use means, methods, and materials that have the lowest "carbon footprint" as possible, and most OPC and related products do not meet even the basic of a low carbon footprint and come from some pretty environmentally corrupt industries.

I often ask students why they have a need to "reinvent the wheel" with their individual projects? Often they spend days and months trying to "make something work" when others have just moved on with the simple solutions of doing it the way is known to work already.

Firebrick and basic kiln building skill will create a wonderfully well made and operational RMH.

Sorry again for being such a downer...Let us know if we missed any or your points or questions.

Regards,

j

Bill Rust : I am sending you to a previous thread where some of the must astute and craver minds tried to create a lightweight shippable Cast core at the Wheaton labs
last november ! They failed big time ! Yours is a qualified success!

Having said that I want you to see how the Rocket burner base was made up. Scroll down until you come to pictures that show the small Doughnut ( The base for the -
Heat Riser! ) And then, the Larger doughnut that shows a ring-like mark where barrel was temporarily set on top of it ! You will see that the between the two doughnuts
there is an inner ring of air space.

After the hot exhaust gases have fallen down the outside of the Heat Riser( and the inside of the Barrel ) there reach the top of the burner Base where the hot exhaust
gases are channeled through the Transitional Area to turn at right angles and flow into the horizontal pipe of the Thermal Mass !

This is one of the most common areas to cause a new builder problems and yours definitely needs to be shaped more ring-like !

https://permies.com/t/29470/labs/rocket-mass-heater-shippable-core

For the Good of the Craft! Think like Fire! Flow like Gas! Don't be a Marshmallow, Your questions and comments are solicited and Welcome ! Pyro-logically - Big AL

Thanks for the honest replies; they are much more helpful than wind blown up my proverbial kilt. I expected some strong opinions about my use of concrete. Since this is my first RMH and because I live in the city and don't have access to clay soil without digging up my wife's beautiful, but tiny garden, I thought to start with concrete and go to clay if it doesn't work. It's not a complete show-stopper if my first effort doesn't work out. If it lasts even a season or 2 of light workshop use, I'll be happy and will have leaned a lot.

Thanks for the tips on right angle bends, packing cob tightly to my flue, and round holes. I think a 30 or 55 gallon barrel would facilitate a round hole better. The small (but 100% free) barrel made certain compromises necessary. Since I have found a source of dry clay powder for $10 a 40 lb. bag recently, I will try raising my barrel to 2" from the top of my heat riser using cob. I don't plan to cook on top of my barrel and will probably put some cob up there too.

Is there a thread on Permies.com that talks about making cob (50/50 clay sand mix) from dry powder fireclay? I can get straw here in the city, but how necessary is it for my application (e.g. covering the top of my cast core and barrel, and packing around my flue pipes, not likely more than 10-12" off the floor?)

Thanks again for the useful, if not brutally honest information!

Before I forget...read this link for thoughts and inspirations....Geopolymers

Go to the top and select searches...there is lots here...

Good luck...and keep posting!

Wow, what an interesting thread! Thanks.

Bill R. : At the top right of this page below the Permies Banner, and above the Permies Video of the Week, is the Permies Tool box! Jay is suggesting that you
find the Toolboxes [Search] Tab, when you click on it it will automatically select a search within the Forum you just left first. Membership has its privileges,
this is available to you 24 / 7 / 365.25 Type a subject in the Search Field,[Structural Cob] and make sure you are searching within permies and follow the
search terms to tons of information from our over 300,000 Forum Threads

While you are investigating the Tool box, click on the [My Profile] Tab, on its new page you will be helped to share the information you feal comfortable with

look at your Name space and L@@K at mine, location information will help us give you more specific and useful information and facilitate finding that Fellow
Member who is a near neighbor with Rocket Mass Heater RMH and/or Cob Experience !

Good hunting and good luck !For the good of the Crafts! Big AL

bill
how is the cast holding up? i am about to cast one similar and i want to know how yours held up, however I'm using a permenant steel mould for the outside of the core, I call it the tub, inside is which the core will be cast permenantly. Also I will be using proper refractory cement and fireplace mortar mixed with perlite, and I won't weaken the cast core with any exhaust ports because the exhaust will exit at the very bottom of the side of my barrel. But I'm curious about the one-piece cast cores and how they hold up with such temperature differentials.

I bet he wants to go bigger.