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I Forge Iron

smoke problem!!


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well, don't know if it's just my set up or what but i've had my forge up and running for a little while now and lately there has been alot of smoke bellowing out of my hood, so much so it is just too bad to stay in my shed. now my query is is it my hood being square at the top stopping the smoke from leaving quickly, or somthing else i'm missing, would i be better off making a new cone shaped hood? any help with this would be greatly appreciated. many thanks Chris.
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Ironclad, here's one thing you might try before doing anything more drastic. Extend some "skirts" down from your hood to block off some of the airflow from the sides and back. I know that puts limits on the size of material you can put in the forge, but it might just help. I had the same problem with an exhaust hood in a laboratory, and extending (in our case, plexiplass) did the trick. There is a HUGE amount of airflow trying to get into the hood all at once. Good luck. :P

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... but i've had my forge up and running for a little while now and lately there has been alot of smoke...

If it worked fine for awhile, and now isn't, I'd look for an obstruction in the chimney somewhere. Perhaps a bird decided to nest up in there.
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With the others; get rid of that choke point!

Go to large diameter flue.

That style of hood is very in-efficient, round or square, you are basically drawing air in from all over and the unheated air lowers the efficiency of the draw in the stack. Look at examples of a side sucker hood which concentrates on just the fire.

If it worked before it could be a case of wind change with the season *or* temperature change. Draft is a function of temperature differential between the stack gasses and the ambient. In cold weather it doesn't take much to get a good differential but in hot weather ambient can be close to what's exiting the stack!

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Heat rises, well Duh!- but it stops rising when it cools. as long as you can achieve that convection, It really doesn't matter what configuration of pipe/hood you use. Some styles work better than others. What I see from your photos first off is the flu reduction to a thinner and non insulated flu. It also seems needlessly tall.

Also, it is better to start with a smaller opening and increase flu size that it is to go with a big opening and reduce flu size.

Allowing enough volume (Pipe Diameter) for the smoke column is important for good convection.

Hope this helps

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Your biggest problems is the 7" diameter outlet on the hood and the reduction of the 10" pipe at the top.
You should have at least 10" diameter opening all the way otherwise you will need blower forced draft setup that is more expensive than necessary.

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Definitely a bigger stack is in order, I'm running 8 inch and it really should be 10 inch. If nothing else, remove that narrow dryer hose at the top of the stack.

Neat blower drive, very cool, fabricate that big flywheel and hanger yourself?

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wow thanks for all the input,great advice from all, will hopefully sort it out with bigger diameter flue also will try the skirts on the sides,maybe with small openings in for longer material. the sizes are 7in going into 7in to 8 and a half double lined pipe then reduced from 8 and a half to 5 up the top, thinking the choking would help the draught!! the blower is called a PIERCE ORIGINAL BLOWER it comes with the larger wheel to drive it usually by a leather strap or belt, but i use an innertube from a bicycle. I think they were used to lite fires in big houses, works fine in my forge, better than the electric blower in the 3rd photo. once again many thanks for the help. cheers chris.

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  • 3 weeks later...

How did I miss this? Consider that blower design shamelessly "borrowed" for reproduction purposes. (Great, another***** project!! :rolleyes: )Thanks for showing it, and a nice close side view to boot! Oh, I'm with the others, by the by. Try a larger pipe, and closer to the heat source.

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Thanks again to everyone, I'm still tweaking it about to see what works best. OddDuck glad you like this blower, it was seized up when i got it from a car boot sale,did alot of stripping down to get it up and running, the shaft for both the big wheel and the drive one were both seized and had to be drilled out and replaced.Also made the two new fins( or blades if thats what there called) the grease nipples were gone also and had to be re-drilled at an angle to make it easier to get at. Am now thinking it might have been better to put bearings in where the two shafts are, would run smoother. Also i attached a sort of bracket to it and shed wall for stability ( A). And ( B ) and ( c ) are the grease nipple points Oh nearly forgot it was reversible (the big wheel)also . Also blows when cranked both ways but better anti clockwise. Thanks Chris.post-16075-0-47471400-1305111748_thumb.j

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Chris,

I agree that you need a larger chimney, however you might try this as a stopgap.

On one of my early forges one of my chaps made up a sort of short 'duct' that was held over the fan intake(covered 90%) and the other end was fitted to the side of an old bucket suspended(by light chain from the hood) over the fire. Then then "recycled" the smoke until the fire was up and running well. this improved the start-up performace and vastly reduced the smoke problem. You remove this contraption when the fire is going well!

Ian

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Thanks yet again, i put sides on this as was suggested and this made a great difference to not only the smokein buy also theres more heat in the fire as well. And removed the top part of the chimney, i will look for bigger flue for this also. Chris.

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