[TheForge] No More Smokin' Hoods

[Andrew Vida]

I will note that the reason for this is because the sudden transition 
from open air to the stack is what causes the right pressure drop.  If 
you have a large hood that tapers to the stack opening, guess what: all 
that air is being corralled into the same place and no drop in pressure 
and therefore no flow...  Bernoulli 101. :)

You could probably get a little better performance if you replaced that 
8" flue with 10 or even 12.  It should suck mo' bettah.

Bruce Freeman had a very interesting contraption set up at his forge.  I 
will leave it to him to disclose or not, but I think the basic idea was 
really good.  Almost fabulous, but if I go that far I'll never see the 
end of his big head, and it's ugly enough at its current size.  No same 
person would want MORE of that.  No insane person would either, for that 
matter.

Trust me.

Peter Hirst wrote:
> Had an AHA! moment in the shop  today.  Since I got the forge up and running over the winter, my special custom-designed open hood has failed miserably.  It covers the entire area of the forge (2x2) and is only about 18" above the fire.  It tapers beautifully to an 8" adapter and is topped by 12 feet of 8" pipe with no cap.  Works beautifully on paper.  In the shop, hardly at all.  Some smoke stays under the hood, and some even goes up the stack, but mostly it just billows and swirls and spills out, even when the pipe itself seems to be  drawing well.     I have noticed several times that at the joint where the hood meets the pipe, it draws like crazy, and even with a  roar when anything flaming is placed near that spot.  Even then, smoke is going the wrong way at the edge of the hood. A lot of air goes up that pipe, but it doesn't take much smoke with it. SO today, when I couldnt stand it any more, out of sheer desperation I took a spare 4' section of 8" pipe and inserted
 it up under the hood at the joint into the existing 8".  That put the lower end, with about a 30 degree angle at the opening, just a couple inches over the fire..  As soon as I connected it, I had a winner.  The fire literally roared into the 8" opening, sucking smoke from at least a 12" radius around it. It may just have been because I was paying closer attention, but the fire seemed to burn hotter, cleaner, and more efficiently.  Things were suddenly so much better that just for grins, I got a nice clean, hot, deep  open coke fire going and dumped a few fat shovels full of green coal  on it.  No problemo.  All that thick, sickly yellow smoke -- and I mean all of it -- disappeared like a wisp into the stack.  
> 
> So now my entire hood and vent system consists of just 16 feet of 8" pipe with  a 30 degree bevel at the bottom.  No side draft, no hood, no expansion chamber, smoke shelf, step down, step up, 12 " flue,  nothing.  Just 16 feet of pipe.   It doesn't interfere visually (in fact I can see the work better than with smoke escaping from under the hood) or mechanically with the fire or the work,  and if it ever does need it for a particular piece, I can either swing it a few inches in any direction or remove it temporarily and rely on the hood.  I was on the verge of ripping out the whole thing and building a side draft with a 12 inch flue from scratch,  and investing in about 12 or 16 feet more of 12" duct for the portable rig for shows.  Now I'm all set with the shop, and for the portable rig,  think I'll just go with the 8" pipe set about 4" over the fire, just like the shop, or maybe resting right on the hearth with the end cut at 45 degrees.  .
> 
> Life just got a whole lot simpler.
> 
> Keziah
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-- 

	-Andy V.

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