Jon Brinley on sun 10 aug 08
Earl,=20
My propane fired FlatTop has a flame about 12-14 inches at peak temp=20
outside the chimney (which is only 4 feet).I have a hole cut in the shed =
roof so hot gases can escape. There is usually some leaves around the=20
edges of the hole, so far they have not caught on fire=20
(roof is 4 feet from top of chimney). =20
My friend and brother in clay Stephen Hawks fired a groundhog kiln for=20
18 years with a Sweet Gum only 20 feet or so from the chimney. Only=20
curled the leaves for a shot time and then recovered. This kiln was =
fired
for about 25 years and still no ill effects to the tree.=20
I know a fan helps aid in draw so it should help in cooling the gases.=20
I have used one when I first built the MMFT. Only to discontinue using =
it=20
once I figured out the best way to gain temp.
Hope it helps
Jon Brinley=20
Sweetgum Pottery
Midland, Ga. USA
Earl Krueger on sun 10 aug 08
I want to build an Olson fast-fire or MFT
of about 1 cu m volume. Wood fire during
the rainy season and propane during the dry.
The problem is I live in a forest. Not just any
forest but one of 100+ ft Douglas Fir trees.
There are some openings between trees which
seem ideal on the ground but when I look up
from these I seem to be in a cylinder with a
circle of blue sky surrounded by many branches.
I don't want to kill these branches with the heat
nor is cutting a tree down an option.
So, does anybody know what the temperatures
would be above a kiln chimney at say 40 ft?
How quickly does the plume spread out?
What if I installed a device above the chimney,
like an upside down pyramid, to break up the
exhaust plume, or perhaps a large fan to dilute
the hot gases?
Any other thoughts?
Thanks...
Earl Krueger
Elmira, OR, usa
Earl Krueger on mon 11 aug 08
Thanks everybody for your responses to
my question. Consensus seemed to be
that either I wouldn't have a problem or I
could resolve it with some ingenuity, sheet
metal and maybe a fan.
I will proceed.
Earl Krueger
Elmira, OR, usa
David Hendley on mon 11 aug 08
There is a huge difference between
> an Olson fast-fire or MFT
Wood fire flames are much longer and greater in volume.
I also live in a forest, but the pine trees were cleared around
my shop building. Instead, probably 100 years ago, oak trees
were planted. So I have a humongous oak tree 10 feet from
my Olsen fast-fire kiln. I would estimate the circumference at
about 10 feet. There is a near-horizontal branch directly above
the chimney. The branch is the diameter of a good-sized tree
and is about15 feet above the top of the 13-foot-tall chimney.
It only made sense to protect this branch, so I installed a heat
shield on it, just a 2' X 10' piece of roofing tin, hung a foot under
the branch with wire.
Of course, there are lots of other smaller branches higher up,
and there are tree branches all around.
After 8 years of firings there was no noticeable effect on the tree,
but the heat shield was deteriorated and falling down. I continued
to fire, and eventually the large branch started burning. This
was not a dramatic event; it just began to slowly smolder.
I fixed the shield and added a second one below it (just another
piece of tin) and the branch was protected again. There were
no noticeable ill effects to the tree and within a year the smoldering
bark was healed. It has been another 8 years since then.
So, based on my experience, I would say that only branches
very close to a chimney need to be protected. At night, at the
peak of a firing, I can see the orange reflection on the leaves
higher up in the tree, but they are unaffected.
I would also say that the heat plume spreads out very, very
quickly. Even on a still day there is enough of a breeze to send
the plume (as judged by smoke right after stoking) off at an
angle. On a slightly windy day the plume never even makes
it into the upper section of the tree.
If I were worried about it, I would make sure to fire a new
kiln only on a slightly windy day the first few times, to get
a feel for how the heat dissipates.
If you have no branches within 40 feet of the top of your
chimney, I would say you should have no problems.
There is, however, a big difference in how different species
of trees react to fire. My big old oak tree is relatively
fire resistant. A pine tree, with its slender needles and
fast igniting pitch, would catch fire more easily. I suspect
that Douglas Fir trees are closer to pines than oaks in
that regard.
David Hendley
Maydelle, Texas
david@farmpots.com
www.farmpots.com
----- Original Message -----
>I want to build an Olson fast-fire or MFT
> of about 1 cu m volume. Wood fire during
> the rainy season and propane during the dry.
>
> The problem is I live in a forest. Not just any
> forest but one of 100+ ft Douglas Fir trees.
> There are some openings between trees which
> seem ideal on the ground but when I look up
> from these I seem to be in a cylinder with a
> circle of blue sky surrounded by many branches.
> I don't want to kill these branches with the heat
> nor is cutting a tree down an option.
Des & Jan Howard on mon 11 aug 08
Earl
We lived in a heavily eucalypt timbered gully for some years firing a 2
Bourry box wood kiln about 1 cu m in setting capacity. The kiln was
built next to a large yellow box which had a footprint nearly as big as
the kiln. The first branches were about 10 metres off the ground, the
kiln chimney came to 4 metres off the ground & during a firing the
internal glow of the chimney reflected off the branches & leaves. The
external flame post stoke was about 1 metre. Even during very hot
summers we fired this kiln & the worst that ever happened was the leaves
& twigs did a merry dance.
Des
Earl Krueger wrote:
> I want to build an Olson fast-fire or MFT
> of about 1 cu m volume. Wood fire during
> the rainy season and propane during the dry.
>
> The problem is I live in a forest. Not just any
> forest but one of 100+ ft Douglas Fir trees.
> There are some openings between trees which
> seem ideal on the ground but when I look up
> from these I seem to be in a cylinder with a
> circle of blue sky surrounded by many branches.
> I don't want to kill these branches with the heat
> nor is cutting a tree down an option.
>
> So, does anybody know what the temperatures
> would be above a kiln chimney at say 40 ft?
> How quickly does the plume spread out?
>
> What if I installed a device above the chimney,
> like an upside down pyramid, to break up the
> exhaust plume, or perhaps a large fan to dilute
> the hot gases?
--
Des & Jan Howard
Lue Pottery
Lue NSW
Australia
2850
02 6373 6419
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