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rocket mass heaters

Temple NH 10 foot yurt RMH - assorted questions

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posted 6 years ago

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Hi - I am building a rocket mass heater in a 10' diameter yurt in New Hampshire.

I played flute too much this summer (Grasshopper and the Ant) - now its getting cold - and I am trying to build a mass in the forest - ha ha.

Was wondering about putting magnesium chloride in the cob mixture to help with freezing. (a friend said that's what they do with concrete.

Also - wondering if there is a preferred orientation for the seam in the 6" stove pipes in the mass.

I will tell the story with pictures (a comedy of learning) but for now I would like to know if anyone has any ideas.

Thank you,

Karl

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thomas rubino

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posted 6 years ago

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Hi Karl; Welcome to Permies!

The seams go up on the pipes. Be sure to bed the pipe well in cob and surround it completely with cob.

I would guess adding calcium chloride might be ok... maybe. That's what they use as a dust control on gravel roads. It is a moisture attractant though, not sure if that's such a good idea.

A better way would be to have a stove burning. Either build your core and plumb the exhaust thru the mass area. Then cob as you burn OR...

Have a small box stove in your yurt that will keep your cob warm enough to build with. Its going to be rough but you can do it. As soon as possible start burning your rmh core and piping , cob and rock lasagna your mass, heating every day.

By the way ... Got DRY wood yet ? You will need it.

Looking forward to photos

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Karl Wilson

Posts: 29

posted 6 years ago

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Hi Thomas,

Thanks for the instant reply - very helpful. I built a rudimentary rumford into the wall which works great for heating me - so hopefully that will help. I built a mass quickly and in a bit of a panic - and think I got the mix too wet - so I am deconstructing. I was curing the mass with my old rocky estufa - piped into the mass - I think that combo will work - good thought on the salt attracting moisture - I think I will give it a miss. Thanks for the seams up info. I will send pictures and the story once I can say "I did it" rather than "I'm gonna do it"!

Thanks again, much appreciated.

Karl

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Karl Wilson

Posts: 29

posted 6 years ago

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New topic - Is pine a legitimate primary fuel source - seems hardwood is preferred.

A friend of mine is having two large pines cut down - and I am looking at them thinking - hmmm - that could be ten years of fuel for free rather than paying for disposal. Big logs which I was thinking I could stack outside as a wind break and then use as needed. (of course won't be dry yet - so maybe next years fuel - though pine seems different (less water - more sap).

Tried searching the forum but have not found a definitive answer.

on a side note - I cut my had pretty badly - spent a night in the hospital (note to self - do NOT put your finger in your mouth!) so all my clay froze - but it has given me time to revisit the videos - and my book arrived the day after so I read the whole book in the hospital (both doctors were interested in the project) - so the delay is going to end up being a good thing - though frustrating....

Also trying to type without a left index finger is challenging so sorry if I have a weird stilted style - ha ha

Thanks,

Karl

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thomas rubino

rocket scientist

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Location: latitude 47 N.W. montana zone 6A

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posted 6 years ago

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Hey Karl;
Pine is fine as long as it is dry. Splitting it down early and stacking as a wind break is an excellent idea.

Normally I burn Red Fir, this year I'm burning pine. Only difference so far is the pine seems to leave more ash in the burn tunnel than the fir did.

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Karl Wilson

Posts: 29

posted 6 years ago

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Another question - I have made a lot of slow progress on the mass - and may have overdone it a bit. Reading Ianto's book I got the impression (falsely??) that more mass above the pipes was better - and in leveling the top - realize that I am more in the 8" to 10" range above the pipes - and now realizing that Ernie and Erica are recommending 5" to 6". I can deconstruct a bit (for the third time - ha ha) - but before I do - I wonder if you have any thoughts. To me it seems like it will take longer to charge, but will also retain it's charge longer, so I am wondering if it seems like a reasonable divergence from the design. Any thoughts appreciated.

Thanks,

Karl

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thomas rubino

rocket scientist

Posts: 6320

Location: latitude 47 N.W. montana zone 6A

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posted 6 years ago

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Hi Karl;
I think your OK. slower to heat up , but longer to release that heat. You can always trim some away if your not happy.
Did you use lots of rock in your mass?
Still waiting for photo's...

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Karl Wilson

Posts: 29

posted 6 years ago

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Yes - lots of rocks - lots of cob around the pipes (probably a bit more than 2") - but lots of rocks on the sides and above - the rocks are what led to the overbuild - leveling to the highest point - and that is without the finish coat. I will try it out and see how it works. I know the rocks are going to make deconstruct more difficult - but I am enjoying the process so I don't mind. Will send pictures when I have a moment - currently basically winter camping and slowly building and curing the mass (as the clay thaws). Read both the books. Listened to the podcasts. But nothing like doing the work to make the information more clear. Funny to be doing this in the winter - ha ha.

Thanks for the help

Karl

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Karl Wilson

Posts: 29

posted 6 years ago

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question of the day:

I am finally beginning work on replacing my cobbled together estufa rocky with a rocket proper (the estufa has been working pretty well). I have a 12.5 inch section of a barrel for the manifold - and another barrel that is 34.5 inches. If my base layer of bricks is 3 inches thick - by my calculations - 47 inches - minus 3 inches at the base - and minus 2 inches above the heat riser - my heat riser ends up being 42 inches - aarghh - is that going to be okay? or do I have to cobble together another ring to raise it to 48 inches? The manifold and barrel as they are fit together nice - so would rather not mess with it. Am I going to end up with a problem???

As soon as I get myself warm - I will send pictures. Including my false starts (which should meet some peoples humor needs)...

Thanks

Karl

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thomas rubino

rocket scientist

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Location: latitude 47 N.W. montana zone 6A

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posted 6 years ago

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Hey Karl;
I would love to answer you... but man I can't figure out your math. Dumb it down for me if you would please.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
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Karl Wilson

Posts: 29

posted 6 years ago

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ha ha

I have barrel that is 34.5 inches tall. I have a partial barrel that is 12.5 inches tall. added together that gives 47 inches for both barrels.

My heat riser will have some thickness of brick underneath it - maybe 2.5 inches.

And my heat riser has to end 2 inches below the top of the "bell" barrel.

This leaves me with a heat riser only 42.5 inches.

But the spec is that it needs to be 48 inches tall.

So I am wondering if I need to figure out a way to make it taller - or if that will be okay. I may need a shorter wood feel (1/3 of the heat riser??)

Does that make sense?

thanks

Karl

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thomas rubino

rocket scientist

Posts: 6320

Location: latitude 47 N.W. montana zone 6A

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posted 6 years ago

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OK; Got your math.
To start,are you are building a stock 6" J tube ?
The measurement of how tall your riser is starts at the bottom of the burn tunnel and goes to the top of the riser. Not just the riser itself.
So at the very least your riser will be 5.5 " taller than you are thinking.

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Karl Wilson

Posts: 29

posted 6 years ago

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hmmm...

Standard 6" J tube.

My barrel (manifold + bell) is only 47". And if I subtract the thickness of the floor of the burn tunnel/heat riser (my brick is 1.25" thick - so one layer would be 1.25") and the gap at the top of the heat riser below the top of the bell (2 inches) - that gives 43.75".

I think that is right...

I suppose I could dig the burn tunnel into the ground - and cut out the bottom of the manifold barrel - and maybe make up the other 4.25" that way... (but I would rather not cut out the bottom of the manifold barrel...)

Sorry if I am being dense...

Karl

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thomas rubino

rocket scientist

Posts: 6320

Location: latitude 47 N.W. montana zone 6A

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posted 6 years ago

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Hey Karl ; I think its me... its late , I need pictures. I'll look this over again tomorrow.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com

thomas rubino

rocket scientist

Posts: 6320

Location: latitude 47 N.W. montana zone 6A

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posted 6 years ago

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Good morning Karl;
My brain works better in the mornings. I get it now. Shorten the height of the feed tube a few inches AND shorten your burn tunnel a few inches . That should compensate for a shorter riser.
By the way I know the book says 2" clearance but that is a minimum, mine is 2.5 " works very well. Most builders are now saying 4" is a safer number.
What are you making your riser out of ?

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
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Glenn Herbert

Rocket Scientist

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Location: Upstate NY, zone 5

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posted 6 years ago

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You say a partial barrel that is 12.5" tall... is that cut off on one end from a standard barrel? If so, the cut end would not be ideal for connecting to the upper barrel. I would turn it over so the original end is up, cut out the flat end leaving an inch all around to stiffen the manifold barrel and give a seat for joining, and add some cob or bricks under it to make it the regulation height.

Karl Wilson

Posts: 29

posted 6 years ago

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good idea - will do that (turn the partial barrel over and build underneath.

in for a cold spell so may be hobbling along with my estufa a little longer... want to be able to take my time and do it right - rather than panicking to get it done and burning again. Having slight lapse of confidence - probably due to cold and sleep deprivation...

riser is firebrick - with perlite cob insulation surrounded by sheet metal

thanks for your great help!

Karl

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Karl Wilson

Posts: 29

posted 6 years ago

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q of day:

best practice for joining manifold to barrel - the video shows some kind of rope like (fiberglass?) gasket - but should I have some kind of clamps or some metal connection - or just seal it with cob? - probably this has already been answered - but maybe you could point me - or I will search. Sorry - having a bit of an off day.

K

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Glenn Herbert

Rocket Scientist

Posts: 4526

Location: Upstate NY, zone 5

574

posted 6 years ago

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If you have the clamp ring that holds barrel lids to barrels, that is supposed to work well. If not, cobbing around the joint would be a quick and easy method which could be removed later if needed for access. There could be any number of other clamping methods, probably involving a band of sheetmetal screwed in place. It just depends on what you have on hand or can easily get. The fiberglass stove door sealant rope would help make the joint smoketight.

Karl Wilson

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posted 6 years ago

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woo hoo - got one day above 32 F - maybe I can get my clay to thaw!

two questions today - inspired by Ianto's book...

1) from pg 28 - the burn tunnel is the "tightest" part of the intestines of the system - so... - my heat riser I have calculated to have 5.3" (5 5/16") interior dimension - square - area - 28.2 sq in. 6" pipe is 28.3 sq in - so that seems good. I am using the flat (9 x 4.5 x 2.25) fire bricks - so if I make my burn tunnel one brick width high - 4.5" - and 5 5/16" wide (to match the heat riser) - I get a burn tunnel with 24 sq inches - but if I add a layer of flat brick (1.25") - for a burn tunnel height of 5.75" - then my burn tunnel area is 30.5" (too big to be following Ianto's advice that burn tunnel is the tightest dimension... I guess I could build it both ways and compare performance... I would like to be able to play around with burn tunnel after the fact - maybe I can...

2) from pg 50 - setting the barrel - Kirk says "moving barrel up and down until it sounds right" - (like tuning a musical instrument) - this sounds like a good idea...

thanks

Karl the turtle

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Karl Wilson

Posts: 29

posted 6 years ago

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continue question 2:

if I make the burn tunnel with four bricks flat (cut them in half lengthwise...) - then I get 5" height - which gives an area of 26.5 sq in. that seems like it might be good.

I know I am overthinking this - but I would like the chance to get it performing well on the first try - and I know subtle things can make a big difference...

but I will learn at any rate. and I DO have a good sleeping bag...

K

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thomas rubino

rocket scientist

Posts: 6320

Location: latitude 47 N.W. montana zone 6A

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posted 6 years ago

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Good Morning Karl; If... you build your burn tunnel not square (not recommended) then do not make it more wide. Build it taller instead . Ash will build up on the floor of the burn tunnel effectively making it shorter. If you already built it shorter then you will have a problem. Yes you could clean it every day but … Why, just make it more tall than wide and it will not be an issue.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com

Karl Wilson

Posts: 29

posted 6 years ago

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hmmm... okay - so if I make it 5.75 high (slightly taller than wide) - I can let the ash make it "tighter" - does that sound plausible?...

thanks for the reply - I think that will be my plan...

K

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thomas rubino

rocket scientist

Posts: 6320

Location: latitude 47 N.W. montana zone 6A

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posted 6 years ago

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Yes that works fine. My own rmh in the green house has a 7.5 wide and 8" tall burn tunnel. Works awesome! Moving the barrel to judge sound is something you want to do outdoors while wearing welding gloves... Not recommended to try this inside your yurt... I suggest you set your barrel at 2.5" if you plan on cooking on it or 4" if its for heating.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
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Karl Wilson

Posts: 29

posted 6 years ago

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good advice - keep it simple - 2.5" - and then I can tinker in the spring summer

thanks much!

excellent advice

K

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Karl Wilson

Posts: 29

posted 5 years ago

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Hi People! I'm back.

And having some issues.

I ended up mostly finishing the mass and rocket last winter - sort of mostly to spec (The J-tube is proper for 6-inch exhaust - the exhaust is three 4 foot sections zig-zagged and exiting at the floor - may have overbuilt the mass a bit...

I am having some performance issues that I need to address before winter comes again.

Firstly - my burn is not as clean as it should be - smoke in the exhaust.

Secondly - The mass seems to not be heating up as quickly as I suspected (I can burn for hours without getting much rise in temperature of mass) - seems as if I am losing too much heat from the barrel. It is "rockety" - but not as aggressively rockety as I was hoping.

Now my design flaws/questions:

My heat riser is not centered in the barrel - due to geometry of fitting the thing in the yurt - whose position is constrained by trees (and the mass being immovable at this point).

I think my "manifold" may be wonky - not smooth enough. It is basically a hole in the base with the 6-inch pipe through the wall and sealed with clay.

I may have to do a complete rethink and rebuild of the j-tube and barrel/manifold - but would like to avoid that if not necessary - because at this point I am not even sure if that is the issue.

Possible a question that my fuel is not optimal (pine building scrap, apple tree trimmings, some hardwood firewood I scrounged). I have been keeping it all dry (mostly) for the whole season (but maybe not dry enough...) I have a rocket cooker outside that burns clean and I can cook with - of course without the mass as a load. Burning the same fuel.

I have photos in a camera - but not the cable to get them on my computer. Will work on that.

But any thoughts or questions or ideas about the general issues. Maybe I could get some help clarifying and isolating the issue(s).

thanks.

Karl

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Glenn Herbert

Rocket Scientist

Posts: 4526

Location: Upstate NY, zone 5

574

posted 5 years ago

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What kind of chimney do you have? Did you just exit straight out the side of the yurt? If you do not have a vertical chimney, you may not ever get good rockety combustion.

I didn't like the taste of tongue and it didn't like the taste of me. I will now try this tiny ad:

rocket mass heater risers: materials and design eBook

https://permies.com/w/risers-ebook