Highlander Anderton

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.

Hope to hear from you soon.

J

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.

J

Hi Peter.
Ok, here is my first list of questions-

Starting from the beginning,

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.

J

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!

J

Wow. that really is interesting. I am intrigued!

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).

J

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?

J

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?

j

Comments?

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...............

Going out to do the test firing.

J