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So you want to build a Rocket Stove or Rocket Mass Heater.  RSS feed

 
David Miller
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Location: Harrisonburg, VA
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Lets start a list of resources for newbies who want to build these awesome stoves, but don't want to die or burn their houses down, much less waste their time and energy. Please contribute links to permies threads, videos, books, everything you can think of as a 'basic starting point" that we can then link to for folks wanting to get involved.
 
Cindy Mathieu
Posts: 242
Location: near Houston, TX; zone 8b
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This is a good idea. First entry is the book:

rocket mass heaters, 3rd Edition by Ianto Evans & Leslie Jackson

This can be downloaded as a PDF or there is a physical paperback of 122 pages.

The paperback is available from many places including our website in my signature.
 
allen lumley
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Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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David Miller : Here is my endorsement for the Rocket Mass Heaters 3rd Edition, This is a great stand alone book after you have read it you can come back here 24/7
to talk with a fellow member and be reasonably sure that you are using the same terms to describe the same part, its size and orientation to the RMH as a whole, and all
the other parts!

By downloading the PDF you can literally have an unlimited number of copies to use within 1 hour of making up your mind to move forward with this project !

I see that you are lucky enough to come to this discussion with pottery experience, for a quick review of what a fire brick is You can look at www.traditionaloven.com

Mostly, The single best thing we can do to be helpful for aspiring Rocketeers, is to warn you that there is a lot of crap out there, especially on You Tube, please have a high
degree of suspicion of any thing you see out there ! Often an individual will post a video of his "Flaming unit of death" and propose to call it a rocket mass heater RMH, we
not only have Zero control over the video, we can be sure that within 6 months someone else will make a copy of the Original ''Flaming unit of death and prouldly post his
or her video on you tube You tube is so hungry for new Video material they will publish ANYTHING ! For the good of the Craft Big AL
 
David Miller
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Location: Harrisonburg, VA
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Thanks Big Al and Cindy, keep the advice for first timers coming. I"m struggling watching Facebook folks building them out of metal and putting them in their homes, with radiators welded to them. In my cringe I'm turning to Permies.com to give them advice so that they don't kill their families and burn down their homes.
 
Wade Smith
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Hi everyone,
I am a fairly new member to the Rocket Heater/J-Tube construction (I have built 2 Rocket Heaters in 4 months) and have a question about the BTU’s per pound of wood being burned in a Rocket Heater. Most all of the charts available on the internet put wood at an average of 8,600 BTU’s per pound of wood for energy output. When I was researching how much heat was being generated by Rocket Heaters for so little fuel being used, the amount of heat, pounds of wood, and total BTU’s did not make any sense what so ever. After doing some MAJOR digging, I ran across a paper that was funded by the EPA and published by Intertek( http://www.epa.gov/burnwise/workshop2011/WoodCombustion-Curkeet.pdf ).
The question I have is what BTU numbers are really correct for burning wood in a Rocket Heater/J-Tube constructed appliance? The EPA funded study says that if you achieve 100% combustion (carbon and gases from pryolysis) you will achieve just over 15,000 BTU’s per pound of wood. If anyone could give me a better source of information, I would appreciate it.
 
allen lumley
pollinator
Posts: 4154
Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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books fungi hugelkultur solar wofati woodworking
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Wade Smith : The diagram on page 4 (marked in the lower right hand corner) is I THINK Wrong. Two homilies come to mind _ 'Statistics prove' (nothing!!) And
Figures dont lie ! ( But Liars Can figure ! )

If you assumed that you were to take the highest value for a perfectly dry 1 Pound of Wood the ~8,600~, reduce Btu capacity by that part of the '1 pound of wood'
that contains 'Free Water' (20%), then we should be subtracting 1,720 BTUs ! 86,00 BTUs - 1720 BTUs = 6980BTUs per pound!

Then if we want to assume we can read the chart on page 4 correctly, we assume that the original chart was figured for BTUs per kilogram, which works out to be
15,2560 per kilo, or 2.2 lbs of wood with a 20% moisture content (Free Water ).

It is a simple and plausible answer and may actually be the appropriate correction, Or Not, damned if I know !

To add to the confusion, soft wood grows faster and is not as dense as almost all slower growing 'Hardwoods' That being said Willow and Poplar/cottonwood are two
fast growing tree species and are both hardwoods!

Softwoods by being less dense are lighter when we measure volume against volume !

As green wood always has a higher moisture content most people who buy wood buy it by 'The Cord' Volume and not by weight as you would be also buying water
with your Wood !

This took lot out of me, I will be retiring early tonight ! For the Craft! PYRO - Logically Big AL !
 
Cindy Mathieu
Posts: 242
Location: near Houston, TX; zone 8b
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The EPA funded study says that if you achieve 100% combustion (carbon and gases from pryolysis) you will achieve just over 15,000 BTU’s per pound of wood.

This is actually an interesting presentation. It does not say 15,000 BTU's per pound.

On page 3, it says 8600 BTU's/pound for hardwoods and 9000 BTU's/pound for softwood. Bituminous coal is 10-14,000 BTUs. Page 11 lists the conditions for good wood combustion. These conditions are the goal of the j-tube combustion system.

For the record, 100% combustion is only possible when using pure oxygen, not the ~19% oxygen atmosphere we are breathing. The upper limit is probably about 95%.

On the Dragon Heaters website, for our "what you can expect" calculations, we used 5,600 - 6,000 BTU/pound of wood. During the intense part of the burn, we recorded 85% to 93% combustion efficiency with Peter van den Berg's j-tube design. These efficiency numbers were logged by a Testo gas analyzer.

It requires vastly different combustion conditions to burn wood than gas. Gas (Propane & Natural) is relatively easy and can be done with a metal jet. The people building metal rocket stoves don't understand or don't want to. They are probably also desperate to lower their fuel bill.
 
Wade Smith
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Hi all, actually Cindy, on page 4, it shows the Purple trace just over 15K BTU if complete combustion is achieved (all carbon and gases) with the Red trace being the more familiar HHV numbers. The only reason I somewhat believe the higher number is that I did build a "metal rocket stove" using an old 100 lb propane tank for a body, 5x5x1/4 wall tube for the J-Tube, Vermiculite (approx 2 1/4 cubic ft) for the insulation tube and a 1 1/2" gap between the insulation tube and the outer shell and a 4" exhaust.
With that said, I have a 2,000 sq. ft. house, the temp outside was 0 F degrees, wind chill was -10 F and the temp in my house was at 58 F when I got home from work. Within 2 1/2 hours of starting the "metal rocket heater" I had the house (bedrooms, bath's, and living room) at 72 degree's F with the 18'x22' great room that the Heater was in running at 85 F. The biggest challenge I had was getting the heat out of the 100 lb shell before going out to exhaust (average exhaust temps ran from 140F to 165F). I ran fans across the steel surface to aid in extracting heat from the shell surface.
That is where the numbers go NUTS.... If I ran the nominal 5800 BTU's per pound of wood calculation, I would have to shove close to 21 lbs of wood per hour into a 4.5" square opening to maintain a 120,000~ish BTU rating just to maintain the 0F outside to 72F inside ratio. If it helps, I was burning Beech, somewhere between 5-8 lbs and hour, zero smoke from the stack, a continuous heavy drip of clear water from the exhaust, and a more white~ish colored than yellow sideways flame was present.
So that is the current dilemma of trying to figure out what the "true" combustion numbers are for burning wood in a Rocket Heater/J-Tube. I am just as much a skeptic as everyone else on efficiency numbers and can only correlate the numbers I witnessed to what's available and nothing seems to add up until I ran the numbers with the EPA study for the "complete combustion" trace in purple on page 4.

 
Wade Smith
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Hi all, just a thought/additional question on why a Rocket Heater/J-Tube produces far more BTU's than what normal wood charts say they do. I remember researching Gasifiers some time ago and someplace between mental wandering and mowing grass, I remembered that back around 1900, the first vehicle was developed to run on "wood gas or commonly known as syn gas". After doing some rough calculations and quick internet search's, I found a quick and dirty reference to how much "wood/syn gas" is in 1 lb of wood. 1lb of wood at 15% moisture content produces 35 cubic feet of gas or 4,900 BTU heat from burning the gas direct ( http://wiki.gekgasifier.com/w/page/6123680/Biomass%20to%20Woodgas%20to%20BTU%20to%20HP%20to%20KW%20to%20MPG%20conversion%20rules). Could this be the missing component/explanation as to why the Rocket Heaters/J-Tube heat output numbers never match the BTU ratings of burning wood?
 
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