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RMH autopsy and redesign modifications

 
pollinator
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Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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John Adamz : Erica Wisner posted to my Forum thread Because Every thing I printed was Not 100% accurate, I had even misread chart, a quoted figures from it
the chart in-accurately inspite of its following the 'expected curve'!

Much of what she has written deals with building to take advantage of the special benefits of Dense fireKiln Brick (different regains have different
names !) And she specifically mentions problems that are created by mixing insulation types and locations, AND insulations! Its a lot to take in, I recommend the
read, it stretched my mind !

1) yes !

2) Ok., assumption time, with a Heat Riser core of any brick it is still necessary to insulate the Heat Riser on the outside, please check back at Erica Ws' carefully
worded insulation types and thicknesses list. about 4 paragraphs below the heading not suitable. she gives several suitable choices that depending on how care-
fully you drill down for bargains in your location, will produce reasonable prices !

3) after you insulate with clay slip and Perlite then you should use a layer of structural cob and then a finish coat to protect your exposures, you are building a type
of masonry stove and need to protect the exposures to include the floor unless you want the floor to be part of your thermal mass AND have no problem with
moisture at that location !

I have no idea what yo been by back ! Big AL !
 
Posts: 126
Location: Springfield, mo
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Allen Lumley- Thanks for taking the time to answer my questions. I really appreciate it. I will reread Erica's post

allen lumley wrote:
Do I understand that you built your heat Riser without using a running bond pattern to allow staggering of your bricks ?


That is correct. If you look closely at the last pic you should be able to see how I stacked them. I plan on doing it over correctly and make it a bit bigger CSA ~34sq" for both the feed and riser. After rereading the book I think it should work to have them both a bit larger than the harder to enlarge burn tube of 29sq". I'm hoping that change will be positive not negative.


3) after you insulate with clay slip and Perlite then you should use a layer of structural cob and then a finish coat to protect your exposures, you are building a type
of masonry stove and need to protect the exposures to include the floor unless you want the floor to be part of your thermal mass AND have no problem with
moisture at that location !


The bottom of my combustion chamber is below floor level. I have some 4" cap blocks under it but it's surrounded by gravel. I only used plain cob little or no straw or anything else to surround it.

I have no idea what you mean by back ! Big AL !


A matter of perspective. I guess I really meant the front end, that which is opposite the burn tube and barrel.
Shown here with the limited cobbing.


original_ash_pit_feedtube.jpg
[Thumbnail for original_ash_pit_feedtube.jpg]
1st_run_riser_no_insul_duct.jpg
[Thumbnail for 1st_run_riser_no_insul_duct.jpg]
 
John Adamz
Posts: 126
Location: Springfield, mo
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I'm done rebuilding the new riser and feed tube. See pic at bottom. It's minus the last course which is only 2 1/2" to get a 2" top gap. Changed from 4.25x6 to 5.5x6. From what I read in the book having a burn tube the former size and the others the latter should not be a problem. Kept almost same ratios. added half brick (1.25") to burn tube length.
I ck'd the gap at the top by putting a clay ball on top of the riser then setting the barrel on. I got lazy and saved some time by not cutting off the extra brick on the riser.

I didn't make it to the brick store Friday for the extra brick I needed to redo the riser and feed tubes, so I had to steal some out of the garage stove til Monday. I've been working mostly at night so pics are not good on my phone. Will get some more Monday.

All I have left to do before firing up is to reinsulate the riser. I could only get vermiculite instead of perlite to replace the fiberglass.
From the book it says to mix clay slip with the perlite 1/6-9 ratio(volume?). At that ratio a 4cu ft bag (~30gal) would need about 3.5+gal of slip! I don't need to use that much but even so that's a lot of water to cook out of the vermiculite/perlite. Can I skip the slip and use just plain vermiculite if I'm filling the 14" duct surrounding the riser? It would be sealed at the bottom and I could cap it with a little cob, or make a metal "lid".
newriser.jpg
[Thumbnail for newriser.jpg]
 
John Adamz
Posts: 126
Location: Springfield, mo
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Just did a little low heat burn with the propane weed torch to slow cure the mortar. I did it with the barrel on. Checked barrel temps and got it a little over 300 for a few minutes, then shut it down.

Another weird thing I observed was I thought due to my uneven convex barrel top (fairly evenly higher on 1 side than the other). I have the riser offset to the feed tube side of the barrel. According to everything I read it should get hotter on the side with the bigger gap. It didn't. Previously I had the highest bulge on top over the riser. A tighter curve to the feed tube side and a more gradual curve to the front/room side. Even after turning the barrel around and putting the lower side over the riser I still get hotter temps on the side with the smaller riser to barrel gap! This difference is only at the top (about 2" down the sides). By the time it gets to the middle or bottom it's pretty uniform.

I was trying to think like a gas and thought that the hot exhaust out of the riser would more easily flow to the highest point of the barrel top (away from the side with the smaller gap and given the barrel top contour) and down to the manifold on the opposite side of the feed tube and in to the exhaust duct to the mass. It doesn't
This is a very puzzling phenomenon. Apparently the nature of gas still eludes me.
 
John Adamz
Posts: 126
Location: Springfield, mo
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Several times now I have continued to use the propane weed torch (which is a high BTU type) pointed in the burn tube to cure the riser mortar and generally heat up the system. Tonight I ran the torch for a while and noticed another weird thing. It got to ~450deg in 10 min, then with the torch at the same output the temps dropped to ~380 after about 45min

I then switched to wood, a very good thinly split oak. It was burning pretty good or so I thought. Got to 500 in 10-15 min, then up to 670 after about 25-30min. Sadly I still did not hear too much rocket sound. The flames looked like there were burning sideways good, no smoke back at all.
The bad news is it soon burned vertically up the wood and created a mountain of coals 5" deep after about an hour:(
It's rather frustrating to put all this work into the heater thinking I had things figured out and end up not much better off than before.

Previously I had a small gap at the bottom of the feed tube to allow air to pass over the coals in the ash pit on it's way to the burn tube. This seemed to keep the coals to a minimum, but it meant I had to balance intake from this area and the top of the feed tube. It worked somewhat well. Now I have a normal vertical feed tube only open at the top.

What I'm thinking now is that because I have yet to ever cob around the feed tube area it's getting too hot and basically causing all the wood in the feed tube to get to the ignition point and burn all at once and incompletely at that. Thus accounting for the huge pile of red hot coals. Of note also is that my ash pit is 2.5" deep. Near impossible to change at this point.
Does this sound possible or likely? Would a solution be using a cob vermiculite mix around the feed tube area say 3"+ thick? Please say yes:)
 
allen lumley
pollinator
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Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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Bump ! A.L.
 
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