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Skilled newbie has questions

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OK, I'm am SOOOO stoked about this! that said, i have read tons voraciously, and at all hours of the night trying to learn everything that I can on the subject.

I will have tons of more questions, I'm sure, but here are my immediate ones:

1.) I love the idea of using recycled materials (ie steel barrel) but have seen many things that don't make sense to me. I have read that these Rocket Mass Heaters can last 20 years... well, if the heat riser (I hope that is the term for the insulated stack inside the barrel) made from wood stove piping. I realize that there will be far less creosote and that sort of thing, but how long can that thin metal last with such high heat? Wouldn't this riser be best made out of a good, sturdy piece of scrap PIPE?

2.) Does the top of the 55 gallon drum last long? or does that extreme heat make that rust out fast?

3.) and what are the benefits of size variables? (I can get a 55 gallon drum as easily as the smaller sizes.) what should i opt for?

4.) what is the relationship between the heat riser/stack and the container (barrel)? does it matter if I put an 8" heat stack in a 55 gallon drum? (what would leave LOTS of space around the stack)

5.) and I have heard many things about about how high the stack should rise inside in relation to the top of the barrel... 1.5 inches, 2 inches, 3 inches... does this ONLY effect the SPEED with which the mechanism heats up?

SO: those were most of my immediate METAL questions... I THINK

now here are my COB questions:

A.) I live in upstate NY. how the heck do I know what percentage of my soil here has clay in it? is this a very general product, or should i try to be precise in clay/sand/straw proportions?

B.) what the heck IS cob? (is it supposed to harden like plaster after drying? -- and of course add insulation and heat retention?)

C.) what is COB's heat retention properties compared to filling horizontal barrels with water and heating the water in the mass?

D.) can I get someone else to do the cob work for me please? ( ha. that's just a joke)

E.) if I design a Rocket Mass Heater for a large room (850 s/f with 12 foot ceilings) how long of a run can I make the exhaust *(mass heater) run? As long as I want? if I make it extra long (say 30 feet) do I need PRIMING vents for the expanse of the run to get the air moving?

F.) and if I use 6 inch galvanized stove pipe for heating the mass, and the "exhaust is mostly CO2 and water, does it rust out right away? (alright... that was a metal question)

and lastly:

with the rocket effect, (I presume it pushes the exhaust out faster than a standard woodstove? right?) how much do winter gusts effect the exhaust flow to the outside? will it blow smoke back into the house, and push flames up into my living space through the J loading system?

If anyone lives in central NY state, near Oneonta, NY, I'd love to stop by to visit and chew the fat about this (if typing is just too burdensome)

thanks for everything, and what a delight to have found this site!
Tim Kelley
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ACK! and I forgot to ask:

if I want to put a large bench/bed mass across my hardwood floor, should I put something like dura rock down first to build on? or tar paper? Could I frame this bench out in WOOD?

thanks again.
Tim Kelley
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and if using firebricks for the underside of the J tube and all that, the firebricks in my outdoor wood boiler break down yearly... if you are building the bricks into a MASS (cob) how do you prevent the bricks from disintegrating with time and having to tear the whole thing apart?
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Location: latitude 47 N.W. montana zone 6A
cat pig rocket stoves
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Hi Tim; I've only built one , so i'm no expert but i'll try to answer as best i can .But first you need a copy of ianto evans book (rocket mass heaters) available as a hard copy or a pdf digital copy. With that book most of your questions would be answered . So #1 , The thin metal stove pipe is sacrificial, it is expected to burn out quickly, leaving a smooth bore of fireclay & perlite. Personally I used an 8" piece of sonitube that burned out with the first firing.The answer is NO about using a piece of steel pipe, it can't hold up to the temps produced in the riser. #2 , The top of my barrel has been glowing orange all winter , with no signs of wear. If you use a barrel with a removable top it could be replaced at a later date if needed. Some people use a piece of soapstone on the top ,some pour a cob top but leave the top sides of the barrel steel to allow the cooling of the sinking gasses.#3 How much heat do you need ? I personally like the 8" size for the longer pipe run (up to 50') and the feed tube is larger allowing a longer burn time between feedings. #4, My heat riser is made with a 16 gal grease barrel with an 8" hole in the bottom a piece of 8" sonitube (always measure in store before buying) and a mixture of fireclay & perlite is packed inside. When the 55 gal is placed over top it leaves a apx 2-3" all around the riser alowing room for your hot gasses to sink into the horizontal transition area (a very important area ) #5, The top gap is variable , what ever works best with your dragon. I have apx 2" gap on mine and it seems to roar quite well. So 2'' , 3" , 4 " what ever works well for you. The bigger the gap the less heat will hit the top of your barrel. Now on to the cob. A, Cob, is sand and clay apx 3 parts sand to 1 part clay seems to be the normal mixture .You must do a settlement test of your clay to see what you have, then make practice bricks with different mixtures and dry them out to see how well they hold up to things like dropping them on the floor or twisting them for strength , this will give you the proper mix of sand and clay. B, see A, C , NO, or better yet think 12 year old children who will work for food (ha,also a joke) Pay them ! E, an 8" system can push apx 50' with each 90 degree turn a 5' deduction. No a dry mass with a vertical chimney should not need any help getting started,but a cold mass can resist drawing and i found that a small fan blowing into the feed tube helped get my draft going. I only had to do that while my mass was wet, after your mass is dry and warm it will be hard to keep your lighter lit when you stick it down in the burn tunnel. F, Use at least one piece or better yet two of regular black stove pipe when you start the horizontal run, then switch to hvac pipe for the rest of your horizontal. I used another piece of black pipe where it exits the mass and starts vertical, then i switched back to hvac to go up and out. All of you horizontal pipe is carefully covered in cob so that WHEN your pipe rots away there will be a smooth bore clay tunnel for the gasses to follow. Yes wind can be a problem for some people, although a tall vertical chimney ,over all obstructions seems to work the best. In closing Get the book ,read up , There are alot of folks someplace in NY state (its a big place) hopefully one will be near you. Good luck Tom
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