[TheForge] Re: forge flues

[Mike Spencer]

> Any idea how to calculate sufficient stack size and height? 

You mentioned in another post that your pipe goes horizontally through
the wall. Did I get that right?  That's going to significantly
decrease the stack effect and require larger diameter flue and/or a
taller one.  IMHO, 8" dia. is marginal at best and won't be enough if
you have a dogleg in the flow.

Back when I got my first big shop, I groveled through such engineering
books as I could find to little or no avail and, after some clever but
non-functional attempts, finally -- I think it was the Mark III :-) --
came up combination of side-draught smoke box and ca. 13" flue.  That
one was ca. 12' or 13' from smoke box to weather cap and worked fine
except when the wind blew steadily from the direction of the big
church across the street.  Then it periodically drew backwards and I
just had to pack it in for the day.

Presently I have the smoke box and about 16' of 13" diameter flue that
only smokes if I forget and turn on the welding exhaust fan without an
door open.  Oh, yes, or if I start the coal fire with a lot of green
coal.  Then I have to stick a couple of sheets of burning newspaper
into the smoke box to get it to draw the smoke that isn't yet hot
enough to initialize the stack effect.  Once I have a hot fire there
almost never a puff of smoke into the shop.

But isn't the internet nice?  Here's the stuff I was looking for in
the engineering books back when:

    http://en.wikipedia.org/wiki/Flue_gas_stack
    http://en.wikipedia.org/wiki/Stack_effect

Not that it's altogether a cookbook procedure; they say:

   The calculation of many of the above design factors requires
   trial-and-error reiterative methods.

The best forge flue I ever saw?  I knew a guy who rented a house in
western Mass. that was on a property shared with an abandoned and
partly demolished small factory.  The original brick boiler stack was
still in good shape, maybe 10' or 12' inside diameter at the base and
4 or 5 storeys tall.  He put his workspace and forge inside and just
propped the iron door open part way.  The draught was stupendous.  If
he opened the door wide, he was working in a minor hurricane.

There was a brick chimney like that near me that was demolished a
couple of decades ago.  I wanted it but I couldn't figure out how to
haul it home. :-)


- Mike

-- 
Michael Spencer                  Nova Scotia, Canada       .~. 
                                                           /V\ 
mspencer at tallships.ca                                     /( )\
http://home.tallships.ca/mspencer/                        ^^-^^