David Hendley on thu 16 feb 06
Yes, I think your chimney is too small and suggest you increase
it to 9" X 13.5". 13.5" X 13.5" would probably not be too big.
I am basing this advice not on any calculations, but from experience.
I have had two wood kilns about this size, which both performed
well. One had a 9'' X 13.5" chimney and the other had a 15"
round chimney, which is an even larger area.
Make sure the bricks are mortared together, with no gaps, as gaps
will sabotage the draw of the chimney. Another couple of feet
higher than 12' might help as well.
David Hendley
Old Farmhouse Pottery
david@farmpots.com
http://www.farmpots.com
----- Original Message -----
> The sprung arch fire chamber is 45x45x45 including the bagwall and salt
> box
> . The firebox is about 36" high with 14"x48" grates at midpoint .The
> firebox
> is therefore 29% of the chamber which (should!) work fine with a good
> sized
> ash pit underneath. The question is about how much chimney I need to power
> this thing. The 4 exit flues are huge to allow downsizing, the gas
> collection chamber is 27"x9"x40"ht with a 9"x9" x8'tall chimmney on top.
> The
> damper is between the chimney and collection box with a total chimmney
> height of about 12'.
steve bogue on thu 16 feb 06
If any of the kiln gods are listening any advice is much appreciated. The
last year and a half has been consumed with building a crossdraft woodkiln.
Why? because a customer traded me 6 new tires for 2500 new hard bricks , a
good trade for a $400 tax deductable investment. I studied salt kilns in
school, and used electrics in the potteries so now it is time to indulge.
The sprung arch fire chamber is 45x45x45 including the bagwall and salt box
. The firebox is about 36" high with 14"x48" grates at midpoint .The firebox
is therefore 29% of the chamber which (should!) work fine with a good sized
ash pit underneath. The question is about how much chimney I need to power
this thing. The 4 exit flues are huge to allow downsizing, the gas
collection chamber is 27"x9"x40"ht with a 9"x9" x8'tall chimmney on top. The
damper is between the chimney and collection box with a total chimmney
height of about 12'. The first firing stalled at c5-c6 and after 18 hours we
ran out of wood. I am quite willing to redo the chimmney to 9"x3.5" if it
needs more power. In hindsight I figured out that adding ONE brick to a 9x9
chimney pattern which gives you the 13.5 is a much more economical use of
brick. That said If a 9x9 will suffice than I'll leave well enough alone.
thanks!
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Ivor and Olive Lewis on sat 18 feb 06
Dear Steve Bogue,
If you read Bernard Leech in "A Potter's Book" you will find a =
discussion about the proportions of a kiln. pp 190-192. Frederick Olsen, =
"The Kiln Book", also has a chapter on Kin design.
I would not like to make any defining statements but consider that heat =
is only generate if you get sufficient Oxygen into the kiln, but what =
you draw in has to get out after it has more than doubled in volume due =
to thermal expansion. So perhaps you might consider enlarging the area =
of the stack passage and increasing the height of the stack. This will =
increase the velocity and volume of air at the hob.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
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