8" or 6" System ?

Hello everyone this is my first post here and I am wanting to build my first RHM in my house { 2000sq ft }and I have a existing airtight {not so airtight} wood stove with a 8" flue pipe and I was hoping that someone could tell me what size of a J tube I have to build in order to have the right air flow. I am planing to build as close to the floor as possible. It will have a bench about 6' long. Or can I build it with a 6" system and get a 6x8 bell and reduce it at the celling box ? And one last question for now building the J tube is it better & cheaper to build out of fire brick or build a mold and make it out of fire clay, perlite & fire cement or what ever you suggest. Thanks David

David Marin : Welcome to Permies.com and sister site richsoil.com and a big Welcome to the Rocket and Wood Stoves Forum/Threads!
With 21,000 fellow members world wide , you should be able to come here 24 / 7 and find someone who wants to talk about why you want to talk
about !

This is a perfect example of why we ask people for their Climate Zone Number if Known ! Much of Arizona is mountainous and if you are at
altitude, the answer is quite different from a low plains environment !

Not knowing the lay out of your house, or the domestic needs for heat that you may have, I would say that you could expect to heat most of your house,
you may need to plan on firing your 8'' system twice a day to make that manageable ! This would be especially true if you tried to go with building
'close to the floor ' the more mass you have the longer you can go between firings. As excited asI am about the possibilities of the bell system unless
you stack massive amounts of dense brick or stone around and, or in them, you will not have as much heat storage. also with the conventional Thermal
Mass Bench you are able to provide more area heat and accommodate more people than with a very short, low mass with a bell.

Rather than think of your Rocket Mass bell as simply a very efficient heating appliance to be tolerated near the center of you home, a Rocket should be
created as a hand-sculpted piece of Built-in-Furnature, a family art piece and be located in the very heart of the home, there it can be easily tended mostly
by ear, and with a watchful eye on the barrels thermometer ! Your Rocket mass heater should be like spending time with a close family intergenerational
friend Not tucked a way in a corner like a troublesome relative you have to take care off. The rocket should be like a well endowed Bank Account into
which your hand places very dry fine split wood and from which you get automatic withdrawals of warming gentle comforting Heat !

Tending your Rocket should be a matter of habit something done by reflex and quickly forgotten, Not a drudges toil, bringing you out of your comfortable
chair to go tend to that wood eating monster that is never satisfied, serving you no better than you serve it !

Again with out knowing more about your layout or house construction and the need to plan to protect exposures ! It would be very hard to make you a plan
with guarantees, As this is your First rocket I would recommend a conventional build with fewer experiments, while you may learn so much doing this that
you may want to experiment with improvements, as this is planned to be a principle source of heat Safe seems like the best plan !

I would also recommend that you go to rocketstoves.com to download your PDF Copy $15 of 'The Book'>' Rocket Mass Heaters', with over
100,000 rocket Mass Heaters created world wide most were made following 'The Book' and 95% of all of the First Builds (that worked) were made following
'The Book' AND I don't make a dime ! Big AL

I have tried to find the sight you are talking about the pdf file for 15.00 dollars but I couldn't find it I need to get this buggy rolling
I live at the 3500 ft and right now it is a whopping 26 degrees out side and dropping now that is cold for me and my 63 year old bones not as cold as some of you folks have to en-dour .

David

David Marin : Being a check cashing senior citizen myself, I walk in your shoes , for the next week it is going down to single digits at night and not seeing
freezing during the Day !

I did check and the site is still up and I think we can blame the usual suspects !

1) rocket stoves.com
this one is the most likely, 'Auto correct' changed what you typed rocketstoves.com into rocket stoves.com

2) rocketstove.com
again a possible slip or 'Auto correct again droping the final 's'

3) rocketstoves,com
the comma key was pressed by mistake and you did not catch it

If you goto > rocketstoves.com you will see a picture of 'The Book' at the top of the page, the first 'add to cart' button immediately below the book
will get you the Downloaded to your computer PDF Copy for $15 you can view it on for computer or print all the copies you need all one Price !

The second 'add to cart button' is to purchase a real copy of the book, there is a shipping charge and you will get you single copy in 7-8 days from
Oregon !

I do not think you will have any more problems, while the various parts of the rocket mass heater have names not familiar to you, there is little
new vocabulary and all the math you need you learned in the 3rd or 4th grade!

Oh yes! they snuck in a new sate of mater, when I was going to school there were only solids , liquids, and gas, now there is a new state of matter
called plasma that they snuck in whiteout telling me ! Read through the material, much of it is just common sense if something is not right to you
come here to Permies and Ask, some times its just a matter of hearing it said a different way to understand it ! If there is a rocket, any kind of a
rocket in your future we will help you find it ! Big Al

David Marin : just to clear up what fire clay is or is not !Fire clay gets its name from the fact that it is more useful to potters/ceramists, because they can expect
to get away with firing it without any major expansion during heating and contraction during cooling, it is this ability to survive 'Fireing ' with out cracking that
makes its good 'fire clay' for potters ! Not because it can with stand higher temperatures, or that it is more anything but durable!

Because it is used mostly by potters,often as an amendment to local clays to reduce the swelling and contractions of local Clays,it it often sold by the generic name
fire clay 60, this basically tells a potter that it will fire well and as an amendment or as a stretcher of a limited resource of good local clay it will improve or reduce
the swelling and contraction of the combined clay !

As a general rule al good potters know about the locations and types of all local clays, even inspecting local excavation jobs where they know more about the way
the local strata lie under the top soil that the guy running the excavator, local clays pick up a folk lore where someone says this will make a good roofing tile but
will break if fired above X degrees F ! But potters have been known to lie to each other ! a local home owner who just wants a few 5 gallon buckets full for a simple
D.I.Y. project may be greeted very hostile-y and even lied to by the College Professor, Church Deacon who thinks 'His' territory is being poached on !

Irreguardless of what you are told or read, 'good clay is a non expansive type clay with a high % of alumina- silicates, and the only way to cheaply tell if this is 'good'
clay or 'bad 'clay is to make a brick out of it and test it for durability !

Much mopre information is available online a good start is the ARTICLES in traditional oven.com ! this is also a good place to look for starter projects ! Big AL