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I Forge Iron

Need some ideas, recommandations and empirical values

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Hi to all out there,

as many people I have a shop that is nice but space is very limitted. My forge is a very compact one and it is mounted on wheels. So I can move it in the shop around when it´s not in use. The other reason for the movability is that I´m going on markets for craftdemonstrations from time to time...

Because I haven´t had a chimney in my shop I have to roll the forge outside, under the free sky and let it run there. Now I like to change this. My idea is to create a chimney thru the sidewall of the shop (indicated on the photo) and to find a way to easily connect/disconnect the hood of the forge to this chimney.

The length of the way the smoke has to pass thru is about 5meters. I would choose pipes of 12 inches ID

What I´m worried about is, if such a chimney will exhaust effectively enough to get the smoke and coal dust out of the shop without a fan? Does anybody have experiences with a temporarily connection between the forge and the chimney?

How did you solve this point? How much chimney should I plan on at the outside?Front.thumb.jpg.efc1947d1073f8a072e4674b93daa56a.jpg




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Horizontal runs are bad. Make it as short as possible. I'd go either straight up (best) or a short run out the back side then up

Height outside should be, if I remember correctly should be 3' above the peak for good draw.

Having to disconnect your hood from the pipe is bad. I would make the hood and exhaust pipe permanent in the shop and just remove the forge.

Since my shops have always been blacksmith shops, my forge, anvil, and post vice have always been permanent. 

I have a second portable forge for demo's.

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That has little to do with draw, specifically, but more with code compliance with standard code.  Of course the code itself is written to optimize a safe and economical installation, but I believe the 3' rule has more to do with fire/heat damage protection and potential reintrainment of fumes than proper vent draw.  If anything, it was written around commercial appliances and fireplaces,  not forge hood fume extractors. Still, it is code in most places and needs to be complied with (see blueprints for Uri Hoffi exhaust installation on this site, and reference the ouside vertical stack after the horizontal wall penetration ).

Anvil is correct regarding limiting horizontal runs and substituting 45 bends for 90s. There are several options for a removable connection between the forge and stack.  A flange connection is probably the easiest to fabricate.  In use, lower down on the stack, the inside of the stack should be at slight negative pressure to the surrounding area  (or no draw), so you shouldn't have to worry about a hermetic seal as you do with a forced exhaust (fan powered).

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I agree with Latticino, go with the Uri Hoffi exhaust. Cut a hole in the wall right behind where your forge sits right now, run a horizontal pipe though it, and go straight up the wall on the outside. I don't know how tall your building is, but it seems like you plan to use a good length of piping anyway. I would then make your current hood and chimney removable to store and use only when you travel. 


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