John Post on thu 27 jan 00
I tried a little experiment while my kiln was firing to cone 2 yesterday.
I turned the exhaust fan on at the beginning of the firing and lit wooden
matches and placed them in front of the peeps and over the air intake holes
on top of the lid. The flames and smoke were pulled in, indicating that
the kiln was under negative pressure as Dave Finkelnburg explains below. I
tried this at room temperature, 1000 degrees F and at 2000 degrees F. The
kiln pulled the flames and smoke in at both room temp and 1000 degrees F.
However, at 2000 degrees F only the bottom peep pulled the flames in. The
top peep and the air intake holes on the top of the kiln were no longer
drawing air into the kiln.
My thinking on this is that as the kiln heats up the heat rises, the air
expands and the fan is no longer able to effectively draw the air in
through the air intake holes. The fan just isn't strong enough to pull the
air through the kiln.
As I said in my original posting, I don't work in the room that my kiln is
in while it's firing. I also have an exhaust fan mounted through a wall to
the outside that takes out any fumes that the kiln vent misses. But I'm
still curious as to whether or not this happens to other kilns that are
vented. Maybe my Orton kiln vent fan is just underpowered for the job. I
ordered it with the kiln when I purchased it and Evenheat who manufactures
the kiln here in Michigan is the one who determined which vent to use with
the kiln.
This isn't really a big issue with me, I'm just sharing my experiences with
kiln venting so that others who are having problems might be able to learn
something from them. However, if this kiln was fired in my house, like
many electric kilns are, I would definitely make sure that I found a way to
make the vent exhaust all of the fumes, not just most of them.
John Post
rp1mrvl@moa.net
Sterling Heights, Michigan USA
>...The idea is to get the kiln under negative
>air pressure. That means, if there are any holes in the kiln, air leaks
>in, not out. As long as that happens, then very few if any fumes from the
>firing should get into the room.
...>During the part of the firing where you burn off organics, the volume of
>gases given off inside the kiln can be significant. The kiln can go
>positive in pressure due to the burning, producing a greater volume of gases
>than the fan can pull off. This isn't likely, but it is possible.
...>Have you made certain your kiln really is under negative pressure when
>you are firing? Easiest way is hold something producing smoke near an open
>peep during firing. If the kiln doesn't pull the smoke in, but rather blows
>it away, you don't have negative pressure in the kiln.
>...Dave Finkelnburg in balmy southern Idaho where the partially thawed
>pond reveals little goldfish swimming about!
John Post
Sterling Heights, Michigan
rp1mrvl@moa.net
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