Forge Chimney?

[Mac53]

I've used a gas forge for a long time, but it is finally time to get one of my coal forges set up in my shop. What have you all used as chimney pipe? I know I want at least a 12" pipe, 4' above the peak, I'm just trying to figure out what to use, and how to not burn my shop down. Any suggestions would be greatly appreciated.

[oldgoaly]

I just have the portable "farrm or farier " forges  6" pipe is what is on there,I have been in the hvac biz for 30+ years. A few factors to consider, how much coal are you going to burn an hour or how much heat are you looking to make?   a guestimate is fine, then how high is you stack / chimney going to be? higher the stack the increase chimney effect? Are you going thru the roof or out a wall?  you will need a wall thimble or a roof flange to isolate  your stack from  wood products. There are  many ways to build one some like a side draft will take more cfm to draw the smoke in, a vented hood overhead is the way many go. Somewhere I have a chimney draft estimator, probably online as well. You can put a damper to limit heat loss when not in use or  working a smaller fire, better be a little large than small. Are you building the forge? got pics?

[lazyassforge]

Mac53, When I built my first forge in the shop, I put a side draft hood on it and used 8" square pipe I made by cutting strips 16" wide and bending it 90 degrees down the center. Then I welded two of them together to make my pipe. I only needed 12 feet from the top of my hood so I used one 4X8 sheet to make the pipe. When I made my wife's forge, I experimented with a "conventional" hood to see which worked better and put a 10" square pipe on it. Even with the small pipe, the side draft hood worked better! Sorry I don't have any pictures of my forges here at work with me to post.

Bill D.

[Branson]

Local codes here in Sacramento call for triple-insulated whatchacallit where the pipe goes through the roof.  I thought it a bit much, but never saw a problem with burnt down shops.  The shake roof over the forge at Sutter's Fort has survived the thirty years I've known it without a hitch.   It's not the pipe you need to worry about, just where the pipe goes through the roof.

[scottg]

I am closely following this, and would love to hear more.

I have this idea.
I have no idea how to build an effective forge but one day I'll build one anyway.
  I am going for ballpark firepot and even rougher ledge around.
River stones of course. I live along a river and the river rolls rocks round, for a living.
I can get river rock.
And I'll probably use some clay/ash mix. I recently used this old time mixture for fireclay to repair and reinforce a wood stove.  And its working fine so far.
I have a large size Champion blower for the forge and an old cast iron ducks nest if I wanted to use it. The ducks nest is currently a doorstop and will likely remain so. I think people figured out more efficient forges since the ducks nest tuyiere? Is that how you spell it? Tue iron?

And......... I have this fantasy hood.   Its a fireplace from the 1970's.
You know, James Bond and M-i-s-s Galore........ lounging at the modern circular fireplace?
  So this thing is about 50-60 inches across and has to be made from 12-14 gauge. It is is very thick steel. It uses 12" stovepipe.

   I just don't know if I want to construct the whole hood suspended ?  Or trim it to a single panel for a back and open the rest up. Reduce the size of the cone in an attractive way?   More like the look of an old stone forge in artist conception geometry?

So my question to the blacksmith inclined is this. I am looking for more of a beautiful thing, but I would like it to at least function minimally as a working forge.
  In other words, I  know I can make it pretty, and I don't need it full time year round, I just need it to work for occasional fun.
Do you think it possible to screw this up so much it won't even work?
    yours Scott

[john k]

Scott, rocks? really?   Remember they can shatter at high heat.   The shops I've been around have found that the size of the hood means almost nothing, its all in the draw of the chimney.   I've seen some side drafts that work extremely well, again its the draft,  and chimney.  The best one I saw was a purpose made brick chimney, with smoke opening about six inches above the fire, worked very well.   A hood seems to take a lot of inside heat, and kinda ignore the smoke.  A tuyere is still the way to go, that or a truck brake drum or a 12 inch wheel.  but with a tuyere you may also get an ash shaker, and clean out.  Use a forge a little bit and you will find how necessary both of these are.   My idea for a forge is an iron tuyere, set down below flush in a 20x24 inch 3/8 plate.  One can always mound up a large fire, and a deep tuyere is just tougher to clean.  Check Pieh tools, online.   A deep tuyere is also useless if you are working with long stock,  the fire has to be above the height of the table.   Just have to build the fire high enough so its all around your work piece.  Have several times been outbid on the old cast  rectangular forge, with a turn down lip along the sides at the tuyere,  so am going to build my own.  Going to a Hammer-In, one can compare 5-6 types side by side. 

[scottg]

The rocks will be far away from the heat. Just veneer trim, for appearance. The fire pot and surrounding shelf will be proper materials. Probably furnace cement and pearlite. Maybe some old kiln bricks too.
  Still have no idea about the hood.

I have a really sad story about an iron forge.
A guy I know found one in the woods. It was hell and gone out there, and it took him 2 weeks hard work just to get into where it was. Then he had to drag it (rather move it Eyptian style with levers and rollers) until he could get it to a truck. Then construct a triangle crane and get it onboard.
It was about 4 feet square and over 1/2" thick cast iron. The fire pot was also iron, super thick, and nearly perfect. It had the trapdoor/T shaker grate for cleaning and heavy steel pipe legs.
He had screwed up his back over it bigtime, and it had never really healed.

Well he was really proud of it, and I was kind of proud of him too. He knew I was crazy about it.
But then one day, on a whim, he sold it for the first 100 bucks that came though the door, along with his anvil and stash of tongs!!!
 
100 bucks. To a total stranger. 
I will never forgive him
     yours Scott   

[john k]

I would of taken him off my Christmas list!!

[JACKP]

Look up info on the Uri Hofi side draft hood. You will find a few images and some discussion.

That is the one I'm going to try in my almost completed smithy.

[JACKP]

Here is a link to the hood. There are many more subjects on this page that any blacksmith will ejoy.

http://www.iforgeiron.com/page/index.html/_/blueprints/uri-hofi-series/bp1048-side-draft-chimney-r175

[keykeeper]

It's my experience that Iforgeiron has as many opinions as Carter has liver pills..lol.I used to spend quite a bit of time there, but found it counterproductive to actually doing and learning the blacksmith skills.

I think the most important factor of any forge stack is that it is big enough to draw, and high enough to produce that draw. Once warmed up, I think it is Bernoulli's principle that takes over....as more heat is produced, velocity is increased due to rate that heat rises, etc. etc. Some smiths will "warm" up their chimney by lighting a piece of news print and laying it just inside the opening while lighting the main forge fire.

Most important is that stack be of an adequate size. Most everyone I know says at least 10" size or bigger. If you are on a budget, you can fit smaller size pipe together at the seams to get bigger pipe, if sound cheap enough. Not sure which two sizes that would take, as I have no stack myself.

The top height of the stack is important as well. If I recall, it should be at least 3 feet above the peak of the building roof the stack goes through to allow proper draw without interference of the structure.

No matter whether it is side draft or overhead style, the straighter the main stack, the better. Any bends to allow for routing through walls, or windows will obstruct the flow.

Scottg: I don't see why that old fireplace wouldn't work to build a forge. Maybe use a round firepot from a brake rotor with fabbed up tuyere? I would do it if I had the fireplace!!! The only drawback to using that duck's nest is no cleanout/ash dump or clinker breaker.

john k: you have some good ideas there!!