Hello Peter and others.
We last spoke some time back, I am sorry for not continuing our conversation and project. I started my own business and it has taken a while to build it to the point that I can get back to my projects.
But now I am back and as the ice and snow are melting outside I am planning to start the big batch fed rocket. I have spent a couple of days reviewing everything from before and will soon begin. A lot of time has passed & I know you guys have been tinkering in the mean time so one question before I start...have there been any significant developments while I was 'away' that I should be incorporating?
I noticed a few youtube videos dealing with pre-heating intake air, for example.
Wonderful
I will take some time to digest the info. Have to go off and do a few days work but will try to source materials at the same time.
Many thanks.
I will have to build the firebox from firebrick so I am trying to work out exact dimensions. If you have those it would save me a lot of guesswork. I have already downloaded the free version of the Sketch up viewer. I now see the P chanel but the cross sectional view does not really give me a good view of where exactly it opens into the riser.
Could I use a metal pipe for the riser? If so how thick should the metal be to withstand the heat?
The diagrams show a double pipe which I assume would be in-filled with insulation, what would be a reasonable diameter for this outer pipe?
At what height would the riser end? In other words how much of a gap should I be leaving between the top of the riser and the brickwork above? (or how long should the heat riser pipe(s) be)
The top part would be tricky but do-able in brick but it could also be cast in fire-proof casting cement (not sure if this is what you guys call refractory cement?)creating a nice curve to roll the heat over and down the sides & yes, I would certainly use mortar between the bricks all the way down the sides as in the original Finnish stove design. I have old, hand made bricks which I salvaged & which I wanted to use (?).
I don't see the door being a problem, I have several old cast iron doors for these ovens in different sizes and most have an adjustable air inlet at the bottom which I can modify to let in the required amount of air, the metal skin of the oven is good grade steel so very weldable if I should need to put in a smaller door than is standard.
There is also a clean-out hatch at the base of the oven (see previous photo). so I will have to add some different brickwork at the base, also to hold up the fire-brick built fire-box. Chimney sweep must have access right through the stove to the base of the chimney for a vacuum hose.
Directly above the stove is the horizontal slit in the wall for the 'Pelti' (is this what you refer to as a damper?) in normal operation of the original stove one would burn one load of wood and when it is down to just embers the 'pelti' is slid in closing off the chimney and retaining the rest of the heat. Are you saying that I should forget this and seal up the slit in the wall?
Looking forward to your reply & a very interesting project which I will fully document.
Peter
Excellent diagrams, fine work.
I already have a multitude of questions but I will study the drawings in detail and then ask everything in one sitting. Because of the nature of this build, with all the brickwork being done inside the metal outer casing and then the next section of the casing being lifted into place and the next stage laid within it, I really have just one shot at this thing so I have to get it right first time. Therefore I hope you don't mind that I am really going to pick your brains to make sure I am understanding everything perfectly. The chimney, by the way, is a touch over 10 meters.
Thanks again and I will post again shortly with questions!
Yes, absolutely I would be interested in a sketch-up design so I can start to really get my head around this. I also have to admit that although I have now read the p-channel threads I still really don't understand what it is, can you explain it or give me a link that explains it to a novice like myself?
the pönttö is 208cm tall and the inside diameter is 70cm. The door is 42cm from floor level and measures 30cm wide by 32cm tall. the hole to the chimney is 13cm wide x 20cm tall and its bottom edge is 6cm from floor level (photo attached).
Well the word kakelugn actually means 'tile oven' so yes those are tiled but the version within a metal skin is still very common, certainly couldn't put this in a museum as I would say that perhaps 10% of houses here have them and companies are still producing the metal shells & colleges are still running courses in how to do the brickwork. The firebox is, I thought, quite big, spanning levels 6 - 13. Traditionally houses would have several of these, each in a different room but clustered around the chimney at the center of the building creating a large thermal mass in the heart of the house, in fact its even called exactly that 'talonsydän' house's heart. They work extremely well, usually you burns one 'pesa' (literally translated this means 'nest', fire box) every other day, even in the depths of winter which can be harsh here, -20 degrees celsius for several months, sometimes -30 and I have seen -40. Yes, Kerros means layer and the name of the Jpeg is indeed Finnish, I scanned the plans and named it Pönttö, these stoves are called 'pönttöuuni' (drum oven). I have also a diagram showing a variation from 1940 but there is no text or layer by layer breakdown. But back to the question. Can you suggest any modifications?
Ok, here are a few images. the first is the outer shell of the drum, the second is the cross sectional views and third is the layer by layer building diagrams.
Allen
I bow to your superior knowledge. You are without a doubt correct about the insulation/sand thing. It is done now and I am going to leave it and see how it goes, It will no doubt effect the burn characteristics but I'll see if I can get the hang of making it work well enough to heat this small space, should be interesting. This is my first rocket, there will be others I am trying to source the light insulation materials you have mentioned but have not yet found them.
Thanks for the tip on which way to load the wood. Its in the book but I forgot. As for the vacuum thing I do not really expect to use it on a regular basis, and I think I have about 7 vacuum motors so I don't think I'll run out.
It is indeed a clean out cap to the right of the rocket at about the 9 meter mark, however, during the rebuild I added another one immediately to the left of the stove where the exhaust leaves the barrel.
Peter
The stove is working with the short stack currently but I am heating it just for short periods each day to 'break it in' and slowly get out the moisture. Later, if it does not work so well I have a long pipe ready to try. But I think you misunderstood, the rocket is not outside, the greenhouse is already built.
Yes, the vacuum is too powerful but I could not resist giving it a try, I already have a nest of bolts welded up for the drip fed waste oil burner but this is really just an experiment. If it works then I will leave it installed just to give myself options, if I should at some point need to really quickly heat the greenhouse in a hurry.
Leonard
I have not seen the P-channel yet, can you provide me with a link?
Ok, I have found all of your help and encouragement invaluable & I will keep you informed how the stove operates. But I would like to ask your advise on my next project. Its not a rocket stove but it is quite closely related. I am renovating my house, when I bought it there was an old "drum-stove" it is a traditional design very common here which incorporates its own thermal mass. Very much like a very big heat riser (210cm tall, 70cm dia.) the fire is lit at the bottom, heat goes up the center to a second chamber at the top (gas burning chamber) and it then sinks all the way down and goes into the chimney at floor level. It was in bad condition & I demolished it & am starting from scratch. I have the original plans (dated 1898).
would you guys consider looking at the plans to see if you can suggest any modifications, using your rocket knowledge?
Ok guys.
The new improved rocket is now done. 14.5 hours yesterday, finished in the dark. Now I will do a test firing and then I'll post the video. About the sand thermal mass, I suspect you are right..........but I did it anyway before I read your messages & I am going to give it a try. I can't help but question the reasoning just a bit despite the fact that you have far superior knowledge and experience here. The water tank is made of 4mm thick steel so it will heat up anyway, if it were filled with insulation then all of its acquired heat would radiate outwards while having thermal mass on the inside means that some of the heat will be conducted inwards thus reducing the surface temperature of the metal surface. Obviously if the rocket is heated for hours on end the temperature would eventually rise to the point that it would compete with the heat inside the heat riser but I should be able to learn how long I can heat it.
So I am probably wrong here but I'm going to try it.
The video will also show one other improvisation that I wanted to try, As Rocket stove purists you may not approve...............
Ok.
The rocket is intended to heat my greenhouse which is 5m x 2.5m. Primarily to extend the growing season and also to give me a warm place for my morning coffee in the autumn & early spring when its chilly. However......If I discovered that my rocket worked well enough to heat the greenhouse through the winter then I would move my chicken hut in there in the cold season when there is no longer enough light here to grow in the greenhouse anyway, thus allowing me to keep the chickens year round instead of having to eat them once the temperature gets low enough that I cannot have them outdoors. Plus my greenhouse would benefit from chicken waste fertiliser.
But anyway, I have built the heat riser just a bit longer than the minimum and I will try it. I know that I am asking a lot with my 11m underfloor pipe with right angles but I am going to try. I have documented todays efforts and will try to upload a video this evening.
I am going to try something else though, let me know if you think this is a terrible idea but I want to add thermal mass to the heat riser itself. Currently it is made from ceramic chimney pipes with rockwool type insulation rapped around it but I am incasing this within part of an old water heater which gives me a gap between the insulation and the inside of this tank. I intend to fill this gap with sand, the idea being that heat can be stored here also for slow release after the dragon has gone back to sleep. I worry a bit about this extra heat source perhaps making the gap between the riser and the outer barrel to warm so that it competes with the heat inside the riser itself but I shall try it and see if it works.
Hello again
Starting the rebuild & I have a question the answer to which I cannot find in the book.
My new build will have burn tunnel with dimensions 9.5cm tall, 10.5cm wide, 49cm long. I am trying to decide on the height of the heat riser. If I use Peters 1:2:4 formula my measurements would be 17.25cm : 34.5cm : 69cm. I would like to take advantage of the barrels I have. As an outer barrel I can use a barrel I have which is 96cm tall. This would give me a significantly longer heat riser. I can, of course, cut the barrel down but I get the impression that the longer the riser the better. Is this really the case or is it only true within certain limits?
The book, page 34, says that "The height in the specimen 8 inch system shown is 33 inches, but could be anywhere from 25 to 50 inches" This seems to indicate that there is an upper limit, if so then how does one work out what that upper limit is?
Peter, I disagree.
While thorough research & preparation are a good (sensible) way to go. Nothing beats trial & error. Having started (and failed) this way just gives me the motivation to keep going & get it working. It took me half hour or so to demolish the stove ready for a 'from scratch' build. Most people waste more than that on watching tv on a daily basis. My failures Just give me a stubborn motivation to keep going and get it right, Which is then fuelled by you guys and your assertions that it can be done. i am enjoying this project very much (I think I have caught the rocket stove 'bug'). Future projects are already forming in my mind- Interested in the rocket stove sauna stove idea & I can't help but think along the lines of making a rocket stove on a big scale............I have access to a grain store, circular, made from old hand made bricks....5.5meters diameter.......heat riser?
Anyway, thanks for your support. I have turned down the offer of work this week so I can get this stove rocketing so updates coming soon.
Hi guys
Upon first reading of 'the book' its obvious I have some challenges. My exhaust pipe is 12cm Diameter which is too small. Unfortunately it is already burried as I needed to get my grow beds in and get my vegetables planted. I still have access to the stove though so I am now faced with the challenge of re-building the stove to work with an 11 meter long exhaust with two 90 degree bends & which is of insufficient diameter to begin with.
So I will completely rebuild the stove such that the burn chamber is correct in relation to the cross sectional area of the exhaust and that everything else relates correctly to the burn chamber.
Allen, yes, there is a difference in types of materials available here & I have to work with what I can get cheaply or for free.
I will document the ongoing process & keep you posted. Unfortunately it will be a few days before I can continue tinkering, real life intruding upon my projects.
Ok
I am off to buy the PDF, will study and get back to you. Peter, many thanks for your suggestions, I am not sure I understand all of them yet but I will work through it and work it all out. Satamax, also many thanks, yep, the concrete blocks must go, I was interested in what you said about 'Horizontal batch rocket' I have not encountered the term before, will do a youtube search but if you have any links I would be most grateful. I'll get this thing rocketing yet!
I am trying to source the light insulation materials you have mentioned but have not yet found them.