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I Forge Iron

Permanent Forge Chimney


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To clarify, the 3 legs of bar stock are bolted to the bottom of the auger pipe with 1/2" grade 5 bolts. The 3 bar stock legs are extended outward to not only set on the decking but to also be over a joist. These legs are then lagged into the wood they set on. This makes for an extremely solid flu entrance. Your crimped end of your stovepipe (vent pipe) now goes in the auger pipe and you make a transitioning piece to hook to the flu from the forge (or the side draft setup I described). You will eventually have to replace the flu cap as they are pretty thin and coal smoke is corrosive (when mixed with rain/snow). The auger pipe is of a thickness that it will last for years and the roof flash should insulate it from discoloring your steel roof.

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Ten Hammers: Thanks. That is very helpful. I had no problem following what you were describing. The space between trusses is 2', which should be plenty of gap. Not sure what auger pipe is, though. Is that a liner used when well digging?

JimG: I expect you are right. However, I recall a discussion quite awhile ago on Keenjunk, to the effect that precipitation almost never comes straight down... it almost always arrives at an angle. That was the principle behind having an outer, wider chimney welded on the top of the external flue. The rain, hitting at an angle would arrive at the inside lip of the flue extension, and just slide down and out the open bottom of the extension... never even touching the real flue. It sounded reasonable to me, but that solution would mean additional area susceptible to leaks, not less. Also, another advantage of the wide outer sleeve was that it left the exhaust completely unobstructed.

I know I departed a good bit from what you were saying. I just meant that the cover would have to be pretty big to cover enough roof to help... and then it could be an exhaust obstruction. That being said... if I use a metal outer flue, I'll probably follow your advice on the cap. :)

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Not sure what auger pipe is, though. Is that a liner used when well digging?

Ed, an auger is just a screw used to move product (in this case, augers used for moving stuff from bin on combine to wagon). Augers are used to move corn from a bin to the truck. A tractor mounted post hole digger is an auger without a pipe. A good commercial roof flash will be what you need. Just talk to an HVAC man (unless of course it's a woman) and they should be able to set you up with a leak proof chimney flash. Thats what they do for a living. Are you planning a ceiling and/or wall insulation for the shop ? Nice lookin building BTW.

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Ten Hammers: Thanks. (One of those forehead slapping motions) I knew exactly what you meant as soon as you described it. I was sitting here thinking of my post hole digger and well-digging... and couldn't place the pipe anywhere on any of it. We used elevators and blowers, but I don't remember using any auger elevators, though I have seen them.

Initially, I don't plan on a ceiling or insulation. I've been working in a pole barn for years, where only one small section is (loosely) enclosed and floored. Just getting out of the wind will be a MAJOR luxury... never mind the space. I had to borrow to do most of this, and I only took enough to get a shell up. Everything else will have to be pay as I go. So you might say, if the shop earns its keep, then it gets to be warm. :mrgreen:

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Ed, I remember that high-efficeincy stack design from Keenjunk, and I tried it. Results, smoke flowed just fine but after a rainstorm I had to get out the sponges and buckets, forge was completely soaked. (apparently we all (myself included) forgot that rain does head straight down on many occasions). Really, unless the rain was light or the wind was blowing more than a gentle brezze, the cap let lots of water in. I went back to tradition and used the peaked hat style of cap, with some basic modifications.

1. added 5" more material to the diameter of the cap so it had a larger area of coverage and,

2. raised the cap another 5-6 inches in height so there now is about 10 inches of clearance for the smoke / wind to blow through between the cap and flue pipe.

In the end, I notice no difference in efficeincy and I wish I saved myself the trouble by initially going with the design that has been in use for the past century, the peaked cap. Live and learn though I suppose :roll:

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At Alfred ABANA in '96 I looked at the smoke stacks and forges provided by Missouri smiths. I copied them at my home forge and they work, especially with respect to rain.

The outside stack runs all the way to the ground and need not have a cap because any water flows to the ground. The bottom straight sections provide the support for the rest of the stack; mine sits on a bed of bricks. The forge stack rises from the smoke box by the forge pot, turns horizontal, exits through the wall, and junctions with the smoke stack using a T. 10" diameter is good enough. 8" is probably too small. Make the smoke stack taller than you think is actually necessary.

If using a shelf to support the smoke stack instead of several straight sections, still use a T junction with a bottom cap. The alternative articulated 90 degree bends tend to rot out from the acidic water collecting in the joints.

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On my chimney, I use a flat cap that is tilted a little toward the normal prevailing rain (which is from the West for us). I have a 12 inch stack, the cap is about 20" in diameter and about 10 inches above the end of the stack - secured by 3 legs. It doesn't keep all the rain out but most of it gets deflected unless there is a gale.

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Stephan: That is VERY interesting. I never heard any follow-up on that discussion before and your comments make a lot of sense. I'm sure this is valuable to far more people than me!

John Larson: Thanks. Without any adult supervision, that design was pretty much my plan because I'd seen it at Bob Kidd's shop years ago and it looked simple and effective. However, I was a wide-eyed neophyte then, and was completely absorbed in the demos by Bob and Peter Ross. I didn't study how good that exhause layout really was, and it's the only one I ever saw personally like it. My interest is that you can put the chimney outside the shop and not have to do any cutting or fitting of the roof. My plan was to build a block/tile-lined 12" chimney and run 10" flue horizontally to it as you described. Maybe I should make a run up to your shop one of these days. There is more than this to learn there, I'm sure! :)

Hollis: No matter what chimney I put up, I suspect I'll follow that general capping plan. Thanks.

Rain rain rain. Can't put the roof on in this weather!

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With all this chimney and cap talk, I called up a buddy of mine who has installed commercial boilers for years (I used to help him as a pipefitter). He reminded me that some stacks have a "double" cap, i.e., the top cap is a slight cone, like the normal coolie hat configuration but there is a small inverted cone fastened to the underside of the large one. This acts as a disperser for the hot exhaust gas coming out and helps with flow. I hope this is clear but picture an 18 inch stack with a 3 foot diameter hat, made with 10-20 degrees slope per side and a 1 foot diameter cone fastened to the underside with perhaps 45 degrees per side. The centers of the cones are aligned with the middle of the stack. The exhaust hits the underside cone and flows smoothly out to the sides.

My friend also said he usually made caps from 20-22 gauge stainless and they lasted forever. He recently replaced a boiler in an installation the two of us did 18 years ago and they re-used the old exhaust. This unit was running 24/7 at a Coca-Cola plant and had already been re-tubed once so it was in hard use.

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Hollis: EXCELLENT! I never thought of that and it makes perfect sense. I fabricated a cone cap (chinaman hat) before and watched the smoke. It sure seemed like more baffle than its benefit warranted. I'll try that next time. I'm aiming at ALL stainless for anything metal outside the shop.

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Hollis and Ed, I have retrofitted several large boilers with the inside cone to make it draw, the best rain cap is one that is almost flat but will still let rain run off. Another thing, the cap should be high enough above the top of the stack so that the area is at least twice that of the area of the stack. with even a slight wind all the smoke will be forced out one side of the opening. A tapered scushion at the very top of the stack will also multiply any wind and make the stack draw much better. And of course don't forget a spark screen.


irn

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