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Rocket flue size?

Satamax Antone
volunteer

Joined: Sep 24, 2011
Posts: 879
Location: Southern alps, on the French side of the french /italian border 5000ft high Southern alpine climate.
    
  12
Hi everybody!

Well, i'm back with my problem. I have a 4 or 4.5 hole through the stone wall of my workshop.

And i would like a rocket.

exerpt form Ianto's book.

"C shoule be the tightest part of the intestinal system. Th esize of the cross sectional areas of all parts of the stove's internal ducts or intestines should never decrease below that of C In other words, the cross sectionalm areas of F,G,H, J and K should all be greater than that of C. Make sure you keep the cross sectional areas of the exhaust stack, the horizontal flues
and the gap at the top of the heat riser bigger than the area of combustion at C, to avoid bottlenecks which could slow combustion
or back up smoke into the room. "

And he also says don't put a chimney damper.


So, i'm stuck with a 4 inch system which is nowhere near eficient enough. Or am i not?

The thing is, gazes retract, shrink when cooling down. This could be to my advantage. Or i could also put a fan in the pipe no?


Just thinking out loud. In case anybody has previous experience or opinion.

Thanks.

Max.


God of procrastination (Pratchett's style) )
Kirk Mobert


Joined: Jan 07, 2011
Posts: 128
Location: Point Arena, Ca
    
    2
Gasses do indeed contract when they cool and stepping down in pipe size is one of the tricks that I use to keep proper flow in a long rocket stove bench run, etc..
You could MAYBE get away with building a six inch system, using a rather long bench run or perhaps bell(s) before piping out the 4 inch hole.
Shame that you couldn't do it with an 8 inch system, but it feels wrong to me.. 4 inch pipe has 1/4 the cross sectional area of 8 inch pipe, though it's roughly (just slightly less than) half the area of 6 inch pipe.
I've found that as a general rule, rocket stoves need an air intake of somewhere between 1/4 to 1/3 system size.. So basically, they're gulping (ambient, room temp.) air at around 1/4 size.. Air expands as it is heated and contracts again when cooled. It means that if you want to shove that air back out a pipe of the same size (1/4) you got to cool it to around the same temp again (or it won't fit) which is not practical and probably quite dangerous as it won't rise up out of a chimney anymore.
(For those of you who understand the physics involved, please excuse the above explanation.. It's not quite accurate, but close enough for our purposes.)
Seems to me that it's do-able to hit the half-size mark, just not quarter size..
I HIGHLY recommend that you try this one outside BEFORE you do it inside. Or at least in a VERY well ventilated space..


Build it yourself, make it small, occupy it.
Satamax Antone
volunteer

Joined: Sep 24, 2011
Posts: 879
Location: Southern alps, on the French side of the french /italian border 5000ft high Southern alpine climate.
    
  12
Donkey wrote:Or at least in a VERY well ventilated space..


Oh, you know my workshop?

Thanks a lot. Well, even a 6 incher can't heat up 1500m² of 18th century vaulted halfunder groundbassement i'm afraid. One question thought. My landlord has an old stove, meant for workshops. Turbo type, they are somewhat similar to pocket rockets. With an air intake on the top and a tube from that air intake to the bottom. I was wondering. Do you think i could fit a heat riser on this? Technicaly, i know i can. I have all the stuff to make it too.

Thanks again.

Max.

Btw, after three edits, i've asken nobody to shove the under  earth level link in my post. I hope i won't see it reapear.
Satamax Antone
volunteer

Joined: Sep 24, 2011
Posts: 879
Location: Southern alps, on the French side of the french /italian border 5000ft high Southern alpine climate.
    
  12
Hi guys.


Donkey, i've been talking with the landlord.  he's chuffed by the thing. Mind you, de doesn't want me to go through the roof, even if i do it properly. And i'm roofer by trade.  Tho, i can use the chimney,  which is a good thing.
I was exhausting through that chimney, but with the bottom open (it's a brick tube assembled outside against the wall) and i had smokeback when it got windy the other day.

So i tried with him with the chimney plugged at the bottom and the draft is luvley on my 4" cyclonic rocket. Found a way to bring hot air from around the barrell to the real workshop part.

And i'm allowed to cut a hole open in the side of the chimney, high up to put an elbow or something for the exhaust. I have to plug it abobe this with rockwool or concrete. So all  might turn ok.

Mind you, i have a cross section in the chimney of 300cm², so i could fit the 314cm² of an eight inch.  Just that i have to go through the 2' of stone wall.  I might do this. But i'm not too keen on digging holes through walls.

Bye.

Max.
Len Ovens


Joined: Aug 26, 2010
Posts: 1274
Location: Vancouver Island
    
  15
I'm hoping to try closing down the flue of my 6inch to 4 inch. I'll let you know how it goes...

Satamax Antone
volunteer

Joined: Sep 24, 2011
Posts: 879
Location: Southern alps, on the French side of the french /italian border 5000ft high Southern alpine climate.
    
  12
Hi guys.

Well, now i have recuperated 6" pipe. But my rocket stove works well, and i don't have enough tube to keep it cyclonic. Which i know i need.

What do i do?

Modify, and go up to six incher.

My heat riser is 139mm and the burn tube and feed tube i've gathered are 150 both internal diameter.

Ok keep as is?
Len Ovens


Joined: Aug 26, 2010
Posts: 1274
Location: Vancouver Island
    
  15
Satamax wrote:
Hi guys.

Well, now i have recuperated 6" pipe. But my rocket stove works well, and i don't have enough tube to keep it cyclonic. Which i know i need.

What do i do?

Modify, and go up to six incher.

My heat riser is 139mm and the burn tube and feed tube i've gathered are 150 both internal diameter.

Ok keep as is?


That should probably be ok... probably have to limit the amount of air intake... though with your design I guess the fuel does that already. If you can put any kind of secondary air through there to past the burn area (just before the riser seems to work for me) it seems to make a difference. Having the secondary air preheated by the burn area is a plus. I found with my 6inch system even a 1.25 inch ID pipe worked well.
Satamax Antone
volunteer

Joined: Sep 24, 2011
Posts: 879
Location: Southern alps, on the French side of the french /italian border 5000ft high Southern alpine climate.
    
  12
Hi Len.

Well, i guess i gonna wait, move it to the insulated workshop, and see if that heats up the 32 square meters to 10/12 degrees, that would be fine. Been thinking about it, and realy, i have work to do and i can't be arsed! I've already done my ecological move today, repaired a hydraulic rolling car jack found in the skip. Instead of reburning it to make steel again, direct recycling is better
 
I agree. Here's the link: http://stoves2.com
 
subject: Rocket flue size?
 
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