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Post by koldenburg on Sept 16, 2012 6:13:49 GMT -8
I've looked around a bit for some RMH plans but it seems everyone is charging for them. This seems ironic given many plans or nearly complete ones are available for masonry stoves. Can anyone direct me to some that are available?
I'm mostly looking for the ratios and measurements that are widely used. I've come across many of those numbers mentioned on this site but no one place that combines them. I don't have a problem paying for Ianto's book but it seems many times I see there has been development that shows many of those numbers aren't necessarily true.
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Post by Donkey on Sept 16, 2012 7:30:09 GMT -8
I don't know of any ready made, free plans. The formula is all here, though maybe a little scattered about. You shouldn't need to buy anything to move ahead.. Maybe just ask the right questions??
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Post by koldenburg on Sept 16, 2012 12:49:47 GMT -8
Okay... So I've read about 6" systems and 8" systems. I assume the idea is this is the interior diameter of the riser tube as well as the diameter of the intake and exhaust? I understand by Peter's drawing that the cut out if a barrel is used must be larger... I haven't seen any mention of pipe length for a bench other than a bell reference that the volume should not be more than 40 cu ft for a 6” system - any numbers there? There seems to also be a magic number for distance from the riser tube to the top of the barrel but by some of Peter's posts it seems that's not necessary if the siphon tube is constructed to get a full burn and would be very detrimental to a masonry bell?
I can tell by my ghetto cinder block test riser that actual fuel consumption it fairly limited unless you're there to feed it once and a while. I like the idea of a brick bell but I'm a bit worried how to enclose it on top. Slabs of my own refractory mix seem questionable. Thanks for your replies.
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Post by satamax on Sept 16, 2012 14:30:58 GMT -8
Koldenburg. May be, carry on experimenting a bit outside. Make a brick or clay burn tunel and metal heat riser, then put a barrel on top.
What i have gathered so far. Gap on the top and sides is important. Under 1.1/4 convection can't beat much friction, and you have a stove which doesn't work well. Usualy people talk about a 2 gap. If you have a 2 gap and side pipe, remember that it's the "ring surface" and not the csa which is important. For example a 6 inch has a circumference of 18.84inch. X 2inch, you have 37 inch of ring and the csa is about 28. So this should be all right. But there's the elbow effect too. Which slows things down. IIRC, on a 8 inch, you van't go over 40' of horiz flue. You can sometimes go one size down to speed up the gasses.
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Post by Donkey on Sept 17, 2012 9:37:27 GMT -8
To figure the gap at the top, I usually do it by sound. I'll get the stove running and let it come up to temperature, then I'll place the barrel over and move it down till the stove stops running, I move it back up till I hear it run well, there will be a "sweet spot" (a position where it runs best), I'll move the barrel past the sweet spot, up and down again till I'm fairly certain I've found it, then I'll have a friend shim the barrel at that spot. I've found that the top gap is usually a little larger than the maths indicate.. Probably due to friction of the "elbow effect"..
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Post by Donkey on Sept 17, 2012 9:41:45 GMT -8
It's the space at the bottom of the barrel that is often forgotten. It's the #1 screw up.
The thing to remember is that the gap sizes are the minimums. Many stoves work quite well with these gaps oversized, few work properly (or at all) with them undersized.
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Post by koldenburg on Sept 17, 2012 12:39:58 GMT -8
Interesting approach Donkey! I have to assume that barrel height doesn't really matter with a high efficiency tube like Peterberg is making. Seems like more space is better in that instance where all combustion is occurring in the riser.
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Post by Donkey on Sept 18, 2012 7:01:06 GMT -8
I don't think that ANY combustion happens in the barrel.. It should mostly happen in the horizontal "burn tunnel", perhaps a little in the riser.. Combustion should be finished by the time anything gets to the barrel.
The barrel is merely a method of harvesting quick heat from the stove.. Some say that the barrel is necessary, they say that loosing heat at the barrel is important for proper flow downward into a bench and such.. I'm not entirely convinced of that.. In any case, you can play with barrel height to change flow characteristics (within limits) and change where the hot spot on the barrel is.. You can do what Peter does and turn the whole barrel thing into a bell stove.
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Post by koldenburg on Sept 18, 2012 7:52:19 GMT -8
Thanks for the clarification. I had read somewhere that someone was claiming the last phase of combustion was taking place between the riser and the barrel which didn't make sense but obviously not a widely held belief. By flow characteristics to you mean velocity or just some sort of sweet spot that is sensed by sound of the fire?
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Post by Donkey on Sept 19, 2012 8:57:45 GMT -8
A sweet spot, sensed by sound, usually. But then: If you set the barrel a little down, the hot spot on the top will narrow and intensify a little, if you set the barrel high, the hot spot will widen and spread.. If you set the barrel WAY up, it will act like a bell. A slightly tighter gap above, if not TOO tight, coupled with a larger space below (quite large) will rush the heat through very quickly.. And so on..
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