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Drunken Dwarf

Coal forge in a shed, in a hanger.

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Hi all.

I'm at the moment kitting out a coal forge in a small space I was able to obtain. My forge is in a 10ft x 8ft metal shed, which is itself inside a storage unit. I have the door of the shed a few feet from the door of the unit (a normal house sized door) with both open so hopefully enough in-draft. My problem is the forge flue, I only rent a space in the unit, I can't put a flue through it and can't really extend anything above the roof line. My only real option is to have a flue coming out of my shed, through a flexible pipe which I put out the unit door.

I understand that I won't be able to get a cross draft which is needed for a passive chimney, so I'll need some sort of mechanical extraction. My other limitation is that I'm trying to run the whole forge on 12V. I've seen 12V extractor fans on amazon, which im thinking "Put some sort of forge hood on, duct it out of my shed to a fan, duct that out the door.". I have no idea if this sort of setup would be sufficient and in all honestly, I don't like the sound of CO poisoning :P

I realize my setup is not exactly ideal, but it's what I have to work with. Any advice would be amazing.

 

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What I've discovered that helps solve the venting issue is to build an enclosure with, a relative small opening, around your forge. I'm assuming it's a coal forge. This helps dramatically increase the draw of the chimney since surrounding colder air doesn't dilute the hot air from the fire. My space is only 33 square feet and( mostly) soundproof. I use a cheap bathroom fan to blow fresh air into my space. Most of my free time is late at night, hence the soundproofing, and no complaints from the neighbors. I'm on my second season using this tiny smithy but so far it's been working out great. Challenging yes, but great,

You can check out my build on youtube. Look for Eviltwinx.

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Tons of various car/truck fans that are 12 V, may want to look at a design that doesn't suck the smoke through the fan (hard on fans); but uses the fan to create a suction by pushing clean air through the duct drawing the smoke along with it.

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ThomasPowers: Yeah, I have an old fan from my ford focus which I was planning to use as the forge blower. So doing something similar for the extraction would be ideal. My problem is that I don't have electricity where I am, so I'm going to be running the forge from a large agricultural 12V lead acid battery. I shall look at that sort of clean air pushing idea. Sort of like the image I've attached is what I have in my head, if you'll excuse the terrible drawing.

mutant: Thanks, I've had a look at your channel and I'll have a go through more of the videos when I have the chance. (I see you've done an Alec Steele course, he's just moved to the states from his home in the same tiny city I live in :) ). I'm impressed you've got it that soundproofed, does the enclosure not restrict your working area a lot? Seems like it'd have the drawbacks of a gas forge in the small opening, and make maintaining the fire harder.

20190308_163436.jpg

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That's the general idea I had, got any friends in the HVAC industry that might make suggestions?

And finally ever thought of going to propane and using NA burners and not needing electricity at all?

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Noone in HVAC now I think of it. That's a gap in my friendship circle!
I have thought of propane tbh, and most of the reasons I want to keep to coal are irrational. Back before I had a space to forge I was planning a mobile forge in a trailer, which would have had to be propane by necessity. But as soon as I had a static place I'd rather a solid fuel one. I don't like the noise of the gas forges, the small openings make it difficult to work on anything with a big bend in it. I have an irrational fear of storing propane because I'm unfamiliar with it :p. Also all I could afford is like, a small devil forge from eBay. And I'm almost embarrassed to say it, but there's a romanticism to a traditional coal fire

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wont be as effective as if the fan was Inline with exhaust fan  will mainly move air from the fan pipe, not much at all from the fire, you are not generating much of a venturi effect this way

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But coal is a recent fuel; only dating back to the high/later middle ages. To be *traditional* you need to be using charcoal!

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A side draft hood and vertical chimney should solve your problems with smoke.  Stack is suggested to be 10 to 12 inches in diameter.  If you have to have a horizontal run of chimney, then add height to the top of the stack. 

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I had a similar situation, not being able to go through the roof line.

I use a squirrel cage blower, which has the motor out of the airstream and a metal blower wheel.  This fan is high static pressure (2 in wg) rated at 450 CFM.  My duct run is roughly 20 feet total of 8” round.  I calculated the area of the opening of my half hood and designed the draw for 100 feet per minute, which is a standard capture velocity for industrial hoods.

In your case, being limited to 12VDC, you may be able use a bilge blower to get a similar cfm rating at decent static pressure.  The problem with most bilge blowers is that the fan blade and motor is inline, and the fan blade is plastic.  They are also really loud and have a terrible whine.

You could try using a tube axial fan, but the minimum size for these type of fans is 12”.  They are expensive as well.

So in short, look for a high static pressure / flow fan with motor out of the air stream, and a fan blade that is metallic.  You can use 8” duct if you have a fan with similar specs to what I listed above.  And please don’t use flex duct, that stuff is garbage for any length of ductwork.

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