Devon Olsen wrote:i THINK that if you were to get a longer exhaust it may create a strong enough draft for you and you may not have to build it with a taller exhaust, so long as it exhausts a couple inches higher than the intake
i think holes may not leak but rather just let in excess intakes and ruin the draftness of it but at 4ft long i think your main thing is just that you need a longer exhaust
and i sorta hear ya there, it seems like every build ive followed the builder finds out its much more difficult than the little bit of knowledge they could find online before building, best of luck with everything though i know how frustrating projects can be when they dont go at all like planned
Irene Kightley wrote:Jamie,
I'm no expert but I've built a heater and it works fine.
I see your exhaust hole in the barrel is the same size as the tube. Everything I've read and believed says that you need a bigger hole in the barrel than you think to get the heat and smoke out of the exhaust. Have a look on the 'net for the actual size.
I used a chimney pot as an exhaust chamber because it was lying around and it seemed to be about the right size. Have a look at the layout in this short video : https://picasaweb.google.com/101842447547367164524/FilmsAndSeriesOfPhotos#5713155398613403762
Irene Kightley wrote:Here's a screen shot from the video
Devon Olsen wrote:i was confused as to what the hole on the top was for as the barrel seemed to connect at the cutout?
Devon Olsen wrote:i see nothing non-RMH about an elevated "chimney" after all the mass
the main reason i would say it is not getting draft would be taht it has no rise at the other end, for GOOD drafting to occur the exhaust has to exit higher than the feed comes in
i would first try simply making sure that the exhaust is higher than the barrel before making it higher than the whole house
the warmed air rising out of the exhaust creates a vacuum of sorts and pulls air through the rest of the setup, if the exhaust isnt higher than the barrel (theoretically the highest point in the design) than the vacuum is weak and doesn't have enough power to really pull it through and create that rocketty goodness
in a cherokee fire pit (im calling it cherokee because i forgot the name of the tribe that did this and it sounds right to me) is basically two holes close to each other and connected at the bottom, burning your fire at the bottom of the lower hole created a draft and sucked the fire up through the second hole, which was higher up, creating less smoke and concentrating heat for cooking, also saving fuel, the fire pit doesn not work very well, if at all, if the exhaust pit is not higher than the burn pit
and i think thats your main problem here, the heat goes to the highest point, working against the draft and slowing it down, also preventing burning past that point because any oxygen that does manage to get drafted in gets smothered with CO2 due to this
Devon Olsen wrote:right... might help if i read a little bit lol
Gerald O'Hara wrote:G'day Jamie,
At the risk of sticking my foot in my mouth I am going to offer some information that may or may not assist you with the "problem".
Before I started building a rocket stove, I spent quite a while trying to find out if there was a specific proportion to the rocket stove components. After "kissing a lot of frogs" I finally found a site from M.I.T. which described the specific proportions required. I will start by saying that my original piece of equipment was a 30" piece of exhaust pipe steel 5" in diameter. The steel was cut into two pieces on the 45 with the short peice being 10" and the longer piece being 20". This was welded together and actually made a reasonably credible rocket stove in that simple configuration. I did take a piece of 4" flat bar and weld that to the inside of the combustion chamber to provide a shelf for the fuel as it entered the stove. As I said, it worked pretty good but not great. It still seemed a bit "smokey" and I wanted to know what I had done wrong.
I found this website and on it was the equation necessary to have a very successful rocket stove. The entire stove depends on the area of the opening into the combustion chamber which in my situation was 5" x Pi. (3.1416) In the equation from M.I.T. the important feature was the diameter of the fire box, such that the diameter of the opening to the fire box is considered algebraically as "X" The horizontal portion where the combustion chamber is situated will now be considereed 2x and the total height of the riser should be x + (1.5 or 2 x) + 5 cm. So in my case the horizontal combustion chamber which was 12" long had to be cut down by 2" and the vertical stack had to be cut down to about 17 ". This gave a much more satisfactory burn and allowed the wood to keep burning as long as I tended it and added more fuel periodically.
Therefore, when looking at the opening in your RMH where the first thing is the rocket stove, it would seem to me that the proportions of the stove opening and the length of the exhaust stack might be mis calculated yielding a goodly amount of smoke.
As I said, I am NO engineer as may be a few of the gentlemen here but in either case, you may want to play some tricks with the math and see if your design meets with important principles needed to fix the problem.
I certainly hope this computes and adquately relays the thought process somehat more clearly.
I hope this helps in your quest to find a good resolution of your rocket stove difficulties.
it sounds like you got some proportion off.
what is the height of the heat riser from the bast to the top?
what is the gap between the riser and the barrel?
how much space do you have in the manifold?
how much space around the rat riser between the barrel and the riser?
how high is the cob around the barrel?
how new is the construction?
How long is the exhaust run?
do you have a vertical or horizontal exhaust?
is the exhaust inside or stuck through the wall?
if stuck through the wall is it insulated?
how sealed up is the burn tunnel, heat riser, and barrel assembly?
I suggest the book
because it can give you an over view of the process and make sure you
have all the parts you need. I to learn hands on but i dont like to
reinvent the wheel unless i have to and thats what the book is for.
our plans are for folks who just want a stove.
1. the heat riser should be around 48 inches tall.
2. from the front of the burn tunnel and fuel feed to the back of the
heat riser inside face of bricks should be 24 inches.
3. a 2 inch gap between heat riser and barrel.
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