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Post by trenchn on Mar 31, 2012 6:17:53 GMT -8
Hi Guys and Gals
Just joined and am planning my first journey in to Rocket Stoves.
I have pretty much decided what I am going to build, but have a few final questions. If anyone can help, I'd be really grateful.
I am hoping to construct a rocket stove heating two hot plates, one dire3ctly over the heat, the other on the left and thus slightly cooler. Both plates will be sealed and the exhaust will then travel up a chimney and away.
I am thinking of building a thermal block stove and insulating with sand. Then building in brick around it to finish off, support hot plates, chimney, etc.
I was going to use stainless steel flue fittings for the sctual stove, combustion chamber, etc, but it is really expensive, so I thought I would try and build it from thermal bricks. My questions are:
1. Is there an ideal length of pipe where you put the fuel/ air intake, before it reaches the elbow?
2. Also is there an ideal length between burning chamber and hot plate?
3. Is the diameter of the tube important? I would like to do one of about nine inches.
4. Is the inside of the tube better smooth or rough. I can sand the bricks I'm using so they are really smooth if necessary.
5. Any other comments and suggestions extremely welcome.
Thanks
Nick
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hpmer
Full Member
Posts: 240
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Post by hpmer on Mar 31, 2012 8:17:40 GMT -8
I think you'd be better off with something other than sand for your insulation as it is a bit heavy. I've had very good results with a wood ash/clay mix. You can use simple stove pipe as a mold around which to pack the mixture and it will fire into a brick like substance that will last long after the pipe has burned away.
I've used an even cheaper (read: free) alternative which were 6" food cans, tops and bottoms removed, and connected with a duct crimping tool, as a form.
I'd suggest you use a "T" rather than an elbow for the turn up into the heat riser, and consider a "J" style stove rather than an "L" which makes for easier fuel loading and potentially more efficient results.
As for your questions:
1. Generally the shorter the better
2. The heat riser should be a minimum of 2x the burn tunnel length
3. The bigger the diameter the more powerful the stove (though 9" seems a bit excessive). I have a 6" version and temps at the top of the heat riser can easily exceed 1200* f.
4. Smoother is better, but I wouldn't obsess over it.
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Post by trenchn on Mar 31, 2012 8:37:09 GMT -8
That's brilliant, thanks.
As I'm building in the garden, not portable, weight isn't an issue unless weight has a bearing on something else. I was just thinking that sand is cheap and plentiful.
You lost me with a "J" rather than an "L", I'm afraid. Is it just the sweep of the join between burn chamber and heat riser?
Does the bottom of the "T" act as a resting place for the ash?
Thanks again.
Are you in UK or accross the Pond?
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hpmer
Full Member
Posts: 240
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Post by hpmer on Mar 31, 2012 8:54:48 GMT -8
More weight = more mass = longer to heat up and less insulative properties.
"L" vs. "J" refers to the fuel loading style. Yours would be a horizontal feeder and require constant pushing of the fuel into the burn zone. A "J" stove uses a vertical feed tube and gravity does much of the fuel pushing requirements. Think of it as another "T" connector on the front end allowing you to load the fuel vertically. The fuel then burns horizontally in what is now your fuel loading tube, but now called a burn tunnel. It should be well insulated as well.
The bottom of the original "T" allows coals to build up, with less emptying of excessive buildup and a hotter fire if you stay with the horizontal feed. Remember, you want air to come under the fuel and as coals build up they choke off this path and allow cooler air to enter above the fuel making for a less efficient and smokey fire.
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Post by trenchn on Mar 31, 2012 9:50:48 GMT -8
Yes, good point!
With a "J" stove, do you still split the fuel feed so that is air entering under the fuel? I have just tried a mock up without this and it was a bit rubbish. Should I have left the divider in?
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hpmer
Full Member
Posts: 240
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Post by hpmer on Mar 31, 2012 10:04:31 GMT -8
No, air enters in and around the fuel. Make sure the feed is well insulated as well. There is also a secondary air improvement detailed elsewhere on the site we call the "Peter Channel" which seems to improve things at the margin, but the original version is pretty straight forward.
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Post by trenchn on Mar 31, 2012 10:44:31 GMT -8
One last question before I drive you copmpletly mad. Does it matter which way the stove faces, is it better for any wind to be blowing into the
Fuel feed?
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hpmer
Full Member
Posts: 240
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Post by hpmer on Mar 31, 2012 14:18:40 GMT -8
Probably, but I can't say for sure. I set mine up in an area sheltered from wind, and use an old bbq grill cover over the top to further shelter the fire. It has holes in the top to help regulate air intake. You can see pictures of it in the thread "My portable maple syrup production facility."
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Deleted
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Post by Deleted on Apr 1, 2012 1:07:34 GMT -8
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