John Hesselberth on wed 21 apr 99
With all the recent discussion on kiln vents, I think just a little of
the dynamics of these systems might be helpful to people. There are 3
basic kinds. 1. a hood over the kiln, 2. a blower located directly
underneath the kiln with ductwork leading to a hole in the wall and 3. a
blower located at the wall or even outside with duct connected back to
the kiln.
In my opinion, #3 is far superior in design concept to the other two.
Here's why. With #1 the kiln fumes/etc. first escape into the room and
then have to be recaptured. Unless the hood is a virtual cyclone, a lot
of the emissions will not be recaptured. It is a very haphazard process
and even you walking by the kiln can stir up enough air to diminish the
efficiency. #2 will work OK if the piping/duct between the blower outlet
and the wall vent is absolutely air tight. This is necessary because the
duct between the blower and the wall is on the positive pressure side of
the blower. If there is even a tiny leak in that ductwork, you will be
blowing the fumes from the kiln back into your studio. Since most people
use dryer vent type slip fittings, it is very unlikely you will get an
airtight system. If you do have this type of system, seal it up very
well.
With #3 the duct that is in your studio is on the suction side of the
blower so the duct is under very slight negative pressure. This means
that if there is a small leak in the ductwork or its fittings you are
sucking in room air and exhausting it through the wall. All the
exhausted fumes still go out through the wall. If it is a big leak, this
will diminish the effectiveness of the system, but a small leak will not
have much effect. The only thing that has to be airtight is the
connection from the blower discharge through the wall.
EnviroVent and KilnVent systems are of type #2; Bailey and L&L systems
are of type #3. My recommendation is that you buy Type 3 if you are
buying new. If you already have type 2 then be sure you have an airtight
system. If you have type 1, replace it or, as one potter told me,
eliminate your exposure to the fumes by evacuation of the potter during
firing.
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"It is time for potters to claim their proper field. Pottery in its pure
form relies neither on sculptural additions nor on pictorial decorations.
but on the counterpoint of form, design, colour, texture and the quality
of the material, all directed to a function." Michael Cardew in "Pioneer
Pottery"
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