Rocket Stove project

Started by glenn-k, December 26, 2006, 02:49:51 AM

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Amanda_931

What I was wondering was--is there an optimum length--or range--for the part under the cob, before the "chimney" starts up?

glenn-k

The book says 20 feet for 6" - 30 feet for 8" and about 5 tons of mass.  Mine hasn't been getting that hot yet so that seems like too much for me but I don't keep after the fire well enough yet.  As I get more wood that is fit for it things should get hotter.

I may need to add more insulation around the fire box too and taking less radiant heat by insulating part of the barrel will send more to the storage also.   I have the air plenum exposed so we'll see in the future what other changes I make will do.



Christopher

These sites may be of interest to some on the list:

http://home-n-stead.com/about/blog.html

This family built a rocket stove/cob bench like Glen's. Go to heading rocket stove

http://www.repp.org/discussiongroups/resources/stoves/apro/Heat/Heating%20Stoves%20LO-RES.pdf

This is a PDF describing the principles of better burning stoves. On pg. 27 they describe the first rocket stove/cob bench built with Ianto. The author says that the underground pipe should only go for 8 ft. maximum. However, Ianto must have tweaked the design, because he can get 20 ft. I found this PDF very helpful in understanding the principles behind the stove.

I was also wondering if you could install a small fan to push air into the chimney after it leaves the floor/bench and goes vertical to create a better draft to ensure that you do not get back drafts. Also if you install a fan, you could probably have more heat risers in series, in order to absorb more heat and make the stove more efficient. I would be interested in knowing what the temperature  is of the gases leaving Glen's chimney. The author seemed disappointed in the amount of heat absorbed by the mass of cob. He suggested using rectangular pipe that would yield more surface area in contact with the hot gases.

I would also like to thank Glen for all the knowledge he shares on this forum. Great work!


jraabe

#53
Christopher:

The Aprovecho information on Rocket Stoves is very well done and quite extensive. The PDF booklet you linked to is great and provides lots of information on building wood heating stoves of any type. They also have other information, videos and sometimes workshops in Oregon.

glenn-k

Thanks Christopher.  

I also am not yet seeing as much heat into the cob as I would like.  The radiant heat from the barrel heat exchanger is good and I was assuming that maybe I didn't insulate the air plenum enough and was losing a lot of heat there rather than getting it to the bench.  

I am pretty sure you could assist the draft with a fan at the far end.  It is used for starting the wood gas generator for running a internal combustion engine, which really operates on the same principal.  It's just that here we are burning the gasses created for heat.  One caution is that the fan should be out on the suction end.  Blowing through it would work but could blow carbon monoxide ito the house.  Suction on the far end will onlu pull air into the system without hurting anything.

From my days soaking in the hot tub in Saline Valley, I would say the exit temperature is about 102 to 105. Feels about the same.  I'll try to get you better information later.  I only have 6 feet of underbench area too in the 3 3x6 inch sections of the decking.  Start of the bench gets pretty warm - rest is only a little warm. :)


smwon

Even though I joined this board in Feb of 2005 I have never posted that I can recall... hadn't been here for awhile either. However, while doing a web search for the rocket heater I can upon this board once more. I am so glad I found it too! I intend to use a rocket heater in a small strawbale house I will be building in the very near future and was having a hard time finding anything on the heating aspect of it... Now here I find not only something about it but a step by step look into how it is done! Thank you!

glenn-k

Glad to see you here and posting.  Be sure to check out Andrews project also.  We are both experimenting to see what these things will do.  

Please keep us updated.


Amanda_931

My copy of the book arrived--along with the silliest calendar I've ever seen--but I can't find it right now.

:(

But I think I read that there really is an optimum (at least minimum) length for the pipe buried in cob.  I thought I would have to run either an s-curve or split the thing in two or three to get the maximum heat out of the mass heater part--in one of the two buildings I'm contemplating.

For the other, the only thing that would work would be the little coffee-maker rocket stove somewhere in the back--and that only if I gave it one of those inverted funnel type chimneys above the burner.  that one is a rocket stove but not a mass heater.

Or maybe experiment with some kind of water heater coil.


glenn-k

Possibly extending the length could help although the exit temp doesn't seem to be that hot.  I made it easy to add to or change so I'll have to get back on it one of these days. :)

Ernest_T._Bass

Did anyone else get confused when putting the insulation container around the heat riser, trying to follow Ianto's book? He never mentions cutting the insulation container to fit around the burn tunnel. He never talks about cutting the feed barrel, either... Maybe it's just me, but I puzzled over those things for quite awhile before going foreword. Don't get me wrong, the book was real good, but there were a few places like that that seemed to just kinda leave me hanging on my own..

glenn-k

Some of that was a bit - do it and figure it out.  I got my clearances worked out then filled with insulating clay/sawdust mix or cob.

In reading it a dozen times I figured that the critical points were fairly clear then the rest were just fit to make the separation of gas flow and sealing as necessary.

jefv

Hi all,

I'm trying to figure out if a rocket stove can be used to heat a sauna. I have planned on building a corwood sauna. Instead of using a ordinary woodburning stove, I want to build a rockets stove. reading the pdf file mentioned earlier, i would probably need a good air to air heat exchanger. I was thinking of putting two barrels in a row. Each of the barrels would be dressed with bricks on the outside to give the whole thing a bigger mass. The bricks do not touch the barrel, but would be seperated from the barrel by a one inch space, with air freely circulating from bottom to top. That way I can directly heat the air, while also storing heat in the bricks, which also act as a heat shield when you are sitting close to the stove.

the things is..... I cannot figure out how big the diameter of the burning chamber would have to be to generate enough heat for a sauna..

Any ideas would really be appericated...

Jef

glenn-k

Welcome to the forum, Jef.  How big is your sauna going to be?  How hot does the air in there need to get?   Does the sauna use dry heat or do you make steam in there too?  I am thinking you won't want to go any less than 8" from my experimentation.



jefv

#64
QuoteWelcome to the forum, Jef.  How big is your sauna going to be?  How hot does the air in there need to get?   Does the sauna use dry heat or do you make steam in there too?  I am thinking you won't want to go any less than 8" from my experimentation.


Dear Glenn,

thank you very much for your message. I'm planning a sauna of 400 cubic feet. I am looking for an air temperature with a maximum of 190 degrees farenheit. And yes, I would like to make steam. I am planning to reinforce or put a steel plate on top of the barrel(s) and load them up with sauna rocks, on which I would be able to pour water to make steam.
Oh, and are you talking about an 8" flue or combustion chamber?

thanks,

Jef

glenn-k

#65
The rocket stove information states that the flue, combustion chamber and entire piping system should have the same area throughout.  It doesn't have to be the same shape throughout but needs the same cross sectional area open so the flow is not restricted.

Remember that part of the successful operation of the rocket stove depends on the chimney temperature and combustion chamber being very high to burn the creosote.  Take your heat off after the insulated stack.

Do you have a design in mind for how you are going to do it.  You may want to go even larger - say 10 Inches if you want to heat faster.  I was a bit disappointed in the heat going into the cob bench  - it only got warm after quite a while running.  Feel free to post drawings, ideas and pictures here.  Temp at the top of the barrel would get to about 350F on a hot burn.  I wasn't too happy with my draft either and that may have held it back from going full blast.  Get to refractory materials - insulated brick or fire brick of some sort for the combustion chamber.  The steel I used was deteriorating pretty quickly in the fire tunnel.  The stack seemed to be holding up pretty well.

Are the rocks going to be up where I cooked the pizza?  Are you planning a similar design?  In a small room I think the rocket would do well and for a sauna room you wouldn't need to heat the earth mass so room temperature could go up pretty quickly.

The room I have it in is very large and drafty and I did it in the colder part of the winter.  The room was 61 feet long - about 16 to 20 feet wide and average 12' ceiling - not well sealed at all, so your performance should be better.

jefv

I think I will go for an 8 inch flue. I think I also need two barrels as heat exchangers to generate the necessary 40000 BTU the sauna is going to need. The pdf file higher up on the board in quite instructive as to heat exchangers etc. Of course, if you cool down the gasses too much, you don't have enough draft.
I'm now thinking about a top loading rocket combustion chamber in combination with heating the primary air with a 1 inch tube that is wrapped around the combustion chamber. The air in the tube will be assisted by a small fan, to blow hot air into the feed tube of the stove. This way I get maximum heat out of the wood I burn. The electricity used by the small fan (maybe 12 Volt), will be minor compared to the gain in performance.

yes, the rocks will go where your pizza goes.... mmmmm .... maybe I could have one barrel with rocks and the other with pizza... yummy!

take care,
Jef

Once I get the to drawing, I'll post it on the board.

glenn-k

#67
Great Jef.  How many places - rough percentage in your country have saunas and what is the normal way to heat them?

I have another idea you may want t play with - it comes from the old heaters used in orchards - how about a re-generator - where a small pipe takes a portion of the flue gas and returns it to the intake to raise temperatures of the combustion chamber - the top has an elbow so the gases flowing up the stack pressurize it sending it down the pipe to the air intake and the small vacuum of the gases drawn into the combustion chamber also pull the hot gases through the re-generator.

The bottom elbow points into the burn tunnel.  I haven't tried this - it may not work.  Depends on how easy it is for you to experiment.

jefv

Only a small percentage has a sauna in Belgium. usually those who can afford it. Other people go to public saunas. I wanted something for myself, in my garden and inexpensive. Also with I wanted it to be as environmentally friendly as possible. Most people heat with electricity, but then you need about 3kilowatts. That is roughly 15 amps at 220 volts. Very expensive if you want to run that for 2 hours

The regenerator idea sounds quite good. i may give that a try.

I was looking at an old oil drum today, but it seems to me that the sheetmetal they make it out of is rather thin. Are you sure it can stand up to the heat? Alos, I was wondering what temperature you get on the outside of your barrel. I want to make sure it get hot enough.

glenn-k

According to the book the barrel will not deteriorate with the heat as the oxygen is used up during the burn in burn tunnel.  I find that to be correct.  My burn tunnel of steel had large flakes of steel oxidizing and delaminating, however the stack which is 1/8" thick steel - 8" dia. showed no signs of oxidation.  I measured the heat on top the center of the barrel with an oven thermometer at 350 degrees when burning hot  -about 250 when not -sides were less and you could touch them quite quickly without getting burned.  The barrel shows heat but no sign of oxidation.  In the book, Ianto mentioned that he expected the barrel to last a very long time.

Thinking about mine - it is in the bottom of the great room - about 6 feet or so below ground  so I am thinking it may have quite an effect on not drafting properly as while the heated air is trying to go up the stack -- outside, it cools enough that it will not want to rise rapidly, plus the cool air inside the stack is trying to fall down as the heated goes up.  My cabin is excavated into the ground so I think the problem is more particular to it.  I have about 12 feet of thin stovepipe stack outside and about 10 feet inside, plus the bench, so I think your arrangement will do a lot better.


jefv

I guess if you use an insulated stack outside, your dreaft problem would be solved...

The temperatures of your barrel, 350 and 250... is that Fahrenheit or celcius? If it is Fahrenheit, i don't think this system will generate enough heat for a sauna. I'll experiment a bit and will let you know.

according to the formula in the pdf file, using two barrels as heat exchangers, I need at temperature of 600 Fahrenheit in both barrels  to be able to get 40000 BTU an hour

glenn-k

That is Fahrenheit.  To keep the temperature up you need to feed it fairly small dry wood and keep after it - In the case of a sauna I would assume every 15 minutes to 1/2 hour.  4 foot long dry boards such as 2x2 inch  or 4x4 inch feed pretty well - the 4x4s would be best after heated up to maintain heat.

I picked up a non-contact thermometer yesterday that goes to 500+ Fahrenheit and will fire mine up to see what temps I can achieve and give you readings from different parts of the heater.

glenn-k

I used to build wood stoves also from a kit a friend developed around 1976.  They were some of the best available.  I think maybe running your barrels horizontal or stacked  horizontal one above the other with good air flow to the fuel may give you the heat you want easier than the rockets stove.  The rocket stove is made for very efficient burning of small quantities of fuel with a pretty good output.  I think you may want a bit more capability to have pretty efficient burning of a lot of fuel for a rip-roaring fire.

You could still use ideas from the rocket stove design and the design of the old stoves I built to make a very hot burning stove using barrels and fire brick or clay to protect the firing chamber area.  The stoves we built had a removable ash pan on the bottom that doubled as under fire air when starting.  There were channels with fire bricks separated for air to go under the fire and an air damper on the back that was regulated by a bi-metal choke spring for semi-automatic heat regulation after the fire was going.  It had an over fire air damper in the door also.  This stove was fire brick lined on and around the bottom and had fins welded to the sides and a second wall outside welded to the fins to create a double wall that moved around 350 cu.ft. of air per minute without a fan.

glenn-k

Another thing mentioned in the book was that for more BTU's you needed to make the system bigger throughout, so that may mean going to 10" or so to get the heat you want with the rocket stove.  Whatever the system size is according to the book, it needs to be the same cross sectional area as I mentioned above.