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Chimney Plan - Looking for Feedback

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Good morning and happy Friday! I've come up with a plan for my forge's chimney and I wanted to run it by you. Hoping to weed out beginner mistakes and make it a decent first chimney. 

I'm going to cut a hole in the shingled shed roof, allowing for a 12" 26 gauge galvanized steel pipe (model #10112616bb on Menards' website) to go straight up. There will be no elbows etc.; straight stack. Since the material available at Menards is galvy, I plan to put the pipe that will be closest to the forge in a 5-gallon bucket vinegar bath. I know zinc fumes aren't released until the metal is quite hot, but I'm all about meeting my grandchildren. I'm going to ask the guys at Menards about a caulk that can stand up to both MN winters and the hot air rising through the chimney. From another post, it looks like a forge at full welding temp gets the air 14 inches up the chimney to about 400 F. 

Because I'm working with an old rivet forge for now, my fire pot is only 8" wide, so I don't plan to use a hood. The 12" pipe opening seems like enough. I'm planning to suspend the opening 14" above the forge, but I'm going to double-check that distance against some forum articles as well. I know that it's a balance between draft and room to work. 

FYI: I'm aware that the 12" pipe is overkill for this size forge, but I'm looking ahead to a larger forge within the next couple of years. 

Thoughts? As always, I appreciate the help getting started. 

Edited by tjdaggett
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I plan on doing the same thing eventually through the roof of my shed smithy. I also shop at Menards as it is only a couple blocks from my house; do they not have non-galvanized black steel piping there? I swear I've seen it before. Hmm. 

I have a book at home that has an illustration and a short story of a guy who made a make-shift temporary forge directly under a tree. He actually hung the chimney from the branches. The name of the book escapes me at the moment, sorry. Personally, I have had a coal forge under low-hanging tree branches for a couple months now. Only saw a bit of discoloring on the bark from the smoke, but I do not have a chimney and lack of sufficient heat was one of the reasons I am now scrapping that forge.  


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If you soak the pipe to remove the galy you will have that section rusted out in no time. 

ideally you are better off with just the galvy and run it up just a little higher so it does not get red hot. 

I have mixed feelings about open suspended stacks vs a solid backed forge stack.   Designed well they work well,. but designed wrongly and they create more smoke then carry away. 

With this the reason why I like a well designed one is access from all points of the forge so can be super handy when doing certain kinds of work like scrolls or larger longer items.. 

For general purpose work the hood design I made up works super well and can be seen in some of the videos on the JLP services inc youtube channel.     It works super well, sometimes to well as outside ends up covered in cinders, ash and soot the stack sucking everything up it. 


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"The Modern Blacksmith" or "The Complete Modern Blacksmith", Weygers  he was using irrigation pipe for his chimney.

I have seen several chimneys that had the ability to either have the hood section go up or down or just have the skirt at the bottom that could be raised for when you need to fit the workpiece through that area.  Currently mine just as a piece of light sheetmetal bent around the base of the pipe held together with baling wire.  It can be raised or lowered as needed. 


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Red Shed, Menards does indeed have black stove pipes in stock! This is why I ask questions. I am very inexperienced with most things hardware; my dad's gifts lie elsewhere. Looks like they only carry up to 9", but Glenn's tip about combining two smaller diameter pipes should solve that problem. 

Thomas, I will probably end up using some kind of a sheet metal skirt in addition to the suspended stack. 


Does anyone have doubts about a 10' straight run at a 12" diameter? I ran out over lunch and confirmed that I can trim the maple tree sufficiently to accommodate such a chimney. 

Edited by tjdaggett
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TJ- you will be ok with a 10' run of 12" pipe. Thats what I'm running in my setup. I did a side sucker- a 4' long 13" square steel box that passes thru the wall of my shed. The stack is mounted on the end of the outside section and is braced to the building. The inner section has a mousehole shaped opening on the end, and it is placed at the edge of my firepot, just a few inches above it. Doing it this way avoided the need for roof penetration and the leaks that usually come along with them. I have a great draft with this setup. By the way, the stack is galvanized and never gets so hot that it can't be touched. The box is welded 10 ga mild steel, painted on the outside.


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Sadly it does not show the overall height. 

Back when I did all the formulas for a forge stack it came out between 12 and 16ft as optimal..   this is vertical run. 

When you add a horizontal section it changes the ratio some. 

I built this stack as a test bed so the back center section could be pulled and modified. 

Out of the 3 that I made as inserts the angled one does the best job.  NO fancy smoke shelf or design other than the taper. 

After this I lost time and left the design alone.  It could use a cinder catch. 

of note..   the On blast performance is not the most important part of the design..    the MOST important is  from no blast (cold fire) to full heat..    This cold transition to hot, back and forth is the most important. 


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From the Hofi blueprint link above

The square tunnel is 13 inches x 13 inches with a 4 degrees down slope to prevent the rain water from flowing back into the fire. The tunnel is some 4 feet long, but it can be 1-2 feet more if needed without any problems. The tunnel is fabricated from 3/16 inch regular sheet metal (black), and painted twice with silver paint. After 15 years it is not rusted yet.

The stainless steel pipes are 12 inches inside diameter. The height of the chimney is 10 feet. In this case I wanted the chimney to go up as near as possible to the end of the roof. You can clearly see it.

On the tunnel there is a 2 inch high coller that the chimney tube is seated on. There is a collar band holding the chimney with straps bolted to the wall. They can be seen in the photo.


There is no rain hood on top of the chimney as it would slow down the air flow. This is the reason for the 4 degrees down slope of the tunnel so that any rain water flows out a drain hole and not into the forge.

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That is pretty much what I have. I have a simple cap for when I'm not using it. I did have one of those wind operated turbine spinnymathings, but strong winds this past spring sent bearings flying all over the place, so I pulled it off and went with (as my son called it) my hilbilly cap.


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I made a nice cap since i did not want water nor snow coming down the stack when not using it.  The trailer sits for a long time between uses. 

the old hood with smoke shelf.  Terrible design. 

Because I work outside with wind blowing every which way, I left the front wider. this also keeps stuff from falling behind the forge hood onto the floor. 

The cap is designed to come part..  I don't really remember why now.   It's width is nearly 12" on each side. 
















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I too like a super sucker. I am building a new smithy and plan to use Torbjorn Ahman’s design he uses 12” stick of pipe (stainless I think). On the inside of the pipe he welded a “shelf” to catch a handle of a rod. The rod has another guide near the top  of a piece of pipe to fit the rod 1/2” is what i plan to use. On top of the rod he welded a “disk” like used in farming. As mentioned the hood rarely get so hot as to not be able to touch, he pushes up the rod/disk and seats it on ledge in bottom of pipe to open flue/stack and lets it down to seal weather out. It uses common inexpensive metal with only a little fabrication 3/4 welds and your open for business. It fits my juckyard stock and my opinion of functionality over looks. Imho. You can see on his youtube page. Be safe and good luck

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Found this in the archive. 

Fellow wanted a traditional brick chimney, wanted it to draw well, but no holes in the roof.  No problem if your a blacksmith. (grin)  Then he remembered someone saying the chimney needed to extend above the peak of the roof. 

chimney 001.jpg

chimney 001a.jpg

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