[TheForge] forge flues

[A Vida]

Experience has shown us (NJBA folks) that 9 inch is pretty much minimal. 
  The difference between 8 and 9 inch flue is remarkable.  There must be 
some threshold of flow that is crossed between the two.  Never bothered 
to do the calculations... in fact, I doubt I'd even recall how to do 
them at this stage of my life. :(

Ten inch would be even better.  No need to go larger though... unless 
you have a much larger fire.

	-Andy

Peter Hirst wrote:
> Good points.  Any idea how to calculate sufficient stack size and 
> height? Mine is 8" pipe eight feet high from the thimble and that is 
> inadequate. It draws just ok when the fire is at its hottest, but any 
> thing less and  it spills smoke.   I know I have to add to it, but how 
> much?
> 
> pgh
> ----- Original Message ----- From: "GRAF" <adveniam at att.net>
> To: "Sponsored by ABANA" <theforge at mailman.qth.net>
> Sent: Wednesday, January 16, 2008 7:13 PM
> Subject: Re: [TheForge] forge flues
> 
> 
>> If the flue is set up with enough size and height it will draw like a 
>> banshee with just the room ambient heat to make it work.
>> Kitchen vents in restaurants don't work without fans because they lack 
>> the stack height usually and have filters which restrict the flow.
>>
>> Mike Graf
>>
>>
>> Peter Hirst wrote:
>>> One more thought if you can stand it.  Something to watch out for: 
>>> "positive ventilation".  I had a fire and health inspector come by 
>>> recently who asked me if my forge was positively (power) vented (it 
>>> isnt).   There is no specific standard in this jusridiction for 
>>> forges (as there is for coal stoves, wood stoves and everything 
>>> else), and the concern was that the flue gases  are NOT HOT ENOUGH to 
>>> draw well.  Just like over a stove or gas grill in a commercial 
>>> kitchen, the heat from an open fire mixes with a lot of ambient air 
>>> on its way toward the hood, and is not very hot at all as it travels 
>>> up the flue.  That's why commercial kitchen hoods are POWERFULLY 
>>> positive vented.  With a coal forge,   this usually means that 
>>> significant smoke escapes the hood and the least back pressure stops 
>>> the draft altogether.  How many of us with coal forges have shops as 
>>> smokeless as a commercial kitchen?  Or as any room with a properly 
>>> vented wood stove? Anybody?  I didn't think so.
>>>
>>> So I would soft pedal the idea that the flue gases don't get very 
>>> hot. This could work against you and lead your inspector to conclude 
>>> that the forge should have a high powered exhaust fan.  Which it 
>>> probably should, but why press it?
>>>
>>> pgh
>>>
>>>
>>>
>>>
>>> ----- Original Message ----- From: "john ortery" 
>>> <bluestoneforge at gmail.com>
>>> To: <theforge at mailman.qth.net>
>>> Sent: Monday, January 14, 2008 7:36 PM
>>> Subject: [TheForge] forge flues
>>>
>>>
>>>> Thanks guys,This seems to be the thought all around.  Most of the 
>>>> people I
>>>> talked to seem to think that as long as you have double wall pipe at 
>>>> the
>>>> exit point and are insulated from any combustible material all 
>>>> should be
>>>> well.
>>>> Thanks again Allen Ortery
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> 
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