Thanks for the screen shot, the mac spreadsheet thing didn't work, so the table is very handy.
Where it says "calculated base" what does this refer to? It seems obviously related to the height whatever it is.
Also the ratio between CSA and height decreases as you go up in system size according to a constant pattern. So the ratio between height and CSA of the 4" system is pretty much double that of the ratio between height and CSA of the 8" system, and three times the ratio of the 12" system.
What the formula underlying this - sorry maths was never my strong point - there is some pattern to it is there not?
The original calculation was done by Jim (jham) from Southern Virginia. This is the thread where he explained his calculations.
He elaborated about it by PM, but I'd think it's alright to publish this here:
Oct 12, 2012 at 6:11pm Hi Peterberg, I wanted to get back to you sooner about the way I attempted to derive the measurements of my stove from your sketchup example but I have been busy at work and home. So....here I go.
I took your measurements and saw that by using bricks in the sketchup model you had made every linear measurement a ratio of a basic unit. Because the clearest ratio you talked about was the 3 to 2 ratio of the firebox opening, I took the firebox opening and divided the height by 3 to use as the basic unit. So 1 unit = 108mm. I then just converted all the linear measurements of your model into multiples of the basic unit. The only measurements that were not a simple multiple of the basic unit was the width and height of the burn tunnel. I just rounded those values (burn tunnel W and H) to simple multiples of the basic unit (108mm) and came up with W=54 (.5 units), H=216mm (2 units). To figure out all the values for my stove I started with the diameter of the heat riser pipe (100mm) I wanted to use, and got the c.s.a of the heat riser 7850mm2. I then multiplied that times 4 for the c.s.a of the firebox and got 31400mm2. To get my basic unit of linear measure for my stove I then took the formula for the c.s.a of the firebox opening and plugged in the numbers I knew: 3 x unknown single unit x 2 x unknown single unit=31400 (the c.s.a of firebox). I then solved the equation to derive the single unit: 6 x unknown unit squared=31400
unknown unit squared=31400/6
unknown unit squared=5233
unknown unit=square root of 5233 or 72mm
I took that basic unit and plugged it in to unit measurements I had figured out from your model. As an example, the heat riser height on your model was 11 units high (108 mm x 11=1188mm) so mine was (72mm x 11=792mm). I apologize if I am not doing a very good job of explaining myself, math is definitely not my native language
I think that this method of scaling worked well because the stove works well. I have sealed and insulated the heat riser more carefully since the last time I posted and the stove is working better than ever. I am going to start a thread today asking for some design help with a planned application. Thank you again for all your data you have shared.
Later on, I've done some recalculations myself and arrived at this conclusion: It is entirely possible to culculate the base dimension by taking 72.36% of the diameter of the riser. So, define the riser diameter, preferably the same as the exhaust pipe, and do this simple math.
Actually, in the model Jim calculated the port is slightly larger than 72% of system size. Minus the overhang of the p-channel it will come down to the 70% target.
The reason why the port is narrower than system size: it promotes a higher air velocity in the port itself and slows down immediately behind it. This do promote a very effective turbulence without adding more air into the fire. Supplying more air as a method to induce turbulence is being used by everyone who like to promote better combustion, with the obvious disadvantage of cooling the fire and enlarging the amount of excess air.
I've tried smaller and wider ports as well, results were not as good. So yes, the constant could be 72.36% but the question of why isn't answered.
Tantalizing, don't you think?
Last Edit: Aug 27, 2013 11:26:27 GMT -8 by peterberg
deadstarsstillburn: Hi there. I was directed this way by folks on the Permies.com website and am hoping I can get some information on how a total newbie can get started designing, siting, building, and not-dying-in-a-horrible-house-fire with a new RMH in a 160-year old home
Oct 21, 2020 6:52:10 GMT -8
deadstarsstillburn: The people over there recommended either a 6" batchbox or an 8" J-tube. I don't know what those are but am going to try to figure that out. What I need is a blueprint that I can scale to fit the need for my house. I have something likne 5000 square feet
Oct 21, 2020 6:53:00 GMT -8
deadstarsstillburn: but I do not need to heat all of it by any means. probably only need to heat half of that, maybe less.
Oct 21, 2020 6:53:15 GMT -8
deadstarsstillburn: moreover, the house has 3 storeys (large attic) so I assume if I get very efficient heating on the ground floor, that will go a long way toward heating the upstairs as well, no?
Oct 21, 2020 6:53:59 GMT -8
BenAlexanderT: Happy new year everybody. I wish you the best
Dec 31, 2020 15:06:14 GMT -8
Solomon: Anybody in Southern Oregon, in Jackson or Josephine counties?
Jan 16, 2021 21:54:43 GMT -8
gnomedome: i realsie this is from 2009
Apr 14, 2021 8:30:44 GMT -8
gnomedome: i realize this is from 2009 id love to see the photos from this ..as im looking to build a sauna soon similar to this .... if anyody sees this post email@example.com..... the photos in this post did not show up
Apr 14, 2021 8:32:00 GMT -8
dcoyte: I am planning to use a cast iron heat exchanger out of a hydronic boiler set on top of my rocket stove, flue out the top. There will be a pump moving the water through the heat exchanger into an unpressurized 2000 gal tank. Any thoughts?
Dec 31, 2021 6:45:55 GMT -8
syekoms: Yes just found this forum am in Josephine county.
Jun 17, 2022 12:53:32 GMT -8
ecoenergyman: Hi new to forum I was wondering where to buy a masonry stove kit I could install myself ? Fran in ireland
Aug 1, 2022 17:39:58 GMT -8
natureman: I have been following this site for years
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Oct 22, 2022 15:15:43 GMT -8
fierolepou: Hi everybody! Starting a project from scratch, this is a goldmine!
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Solomon: Best way to not die in a house fire is to build a stove where the really hot stuff isn't near the flammable stuff.
Jan 10, 2023 11:34:39 GMT -8
beppe: Hi to everybpdy. I'm new about the rocket stoves and this forum
Aug 30, 2023 22:17:32 GMT -8
beppe: I have a living room+ kitchen of 75 square meters that was heated by an ordinary pellet stove with a power of 8KW.
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beppe: I want to switch to a DIY pellet rocket stove but I haven't found yet a project that is really suitable for my situation. Is there anybody able to indicate to me a good detailed project?
Sept 4, 2023 9:05:15 GMT -8