Tip #71: All About Kiln Vents
We often get questions about Kiln
Vents. The most common being, "Do I need one?" Any
kiln that is located in a room where people are, should definitely be
vented to the outside for safety reasons. It is also a good idea in
rooms that are attached to living spaces, such as an attached
garage. But beyond that, a vent makes it much easier to fire the
kiln and provides better results.
1. Safety and Comfort:
Removing fumes from your work
environment is important, since these are unhealthy to breathe on a
regular basis. All products fired in electric kilns contain organic
materials that make carbon monoxide and other fumes when they are burned.
These include clays, glazes, decorating products, decals and the like.
Fumes released may contain sulfur oxides, hydrogen fluoride and metal
vapors, depending on the products fired. Carbon monoxide can cause
headaches and nausea. Other fumes can also potentially cause health
problems. For example, glazes may contain chemicals such as lead and
manganese which are not safe, at least in large quantities or on a regular
Sometimes you may actually notice a
smell when you fire your kiln. Usually this comes from organics
burning out of the clay. And if you use newspaper or wood or other
structural supports which burn out in the kiln, the smells will be very
2. Ease of Firing:
If you don't use a vent, you have
to prop the lid of the kiln at the early stages of bisque firing to allow
the moisture to escape. Since most kilns now are sold with
electronic controllers, having to manually do this step kind of defeats
the purpose of having an "automatic" kiln. It is much
easier to start the vent when you start the kiln, and not have to remember
to close the lid after a few hours.
3. Improving your Fired Product:
Glazes work best when the organics
have been burned out of your clay at the bisque stage. The best way
to ensure that is to do a slow firing with a lot of air flow. The
vent helps remove the organics as they are burned out. You will
usually find you have fewer glaze defects when you have fired your bisque
slowly, with a vent.
Glaze colors can also be affected
by these fumes. C
Sometimes colors that are fired
close to each other will affect each other (cross contamination).
This is significantly reduced with a vent.
Many bright glazes, like reds, need
a lot of oxygen to develop their color. One customer used a lot of
reds and was often having bad results where the glazes would came out
pink. He added a vent to his kiln and his reds became very vibrant
4. Extending the Life of Your Kiln
The same fumes that are harmful to
you also cause corrosion on your elements, kiln sitter parts and
thermocouples. Pulling those fumes out of the kiln reduces the wear
and tear to those parts.
Vents are 20% off through February 06
Q. If I live in a residential
area and I vent outdoors, am I harming or bothering my neighbors?
A. Once mixed with outside air, the fumes are very small
concentration, probably not enough to be detected and certainly not enough
to be a health hazard. Remember that by the time the exhaust gets
outside, it is already mixed with room air by the vent.
Q. What will happen if my
exhaust ducting leaks?
A. All major vent manufacturers now have the fan motor mounted away
from the kiln. This allows the fumes to be pulled from the kiln,
rather than pushed. These are called "negative pressure" systems.
The main safety advantage of this is that should you have a leak in the
duct, the fumes do not leak out into the room. Instead, additional
room air leaks into the duct further diluting the fumes before it is exhausted
Q. How do I install the vent
You drill a few holes, usually at the top and bottom of your kiln.
The vent exhaust connection usually goes under the kiln in the space where
the stand is, although it is possible to mount it on the side.
Ducting runs from the kiln to the fan-motor, then from the fan-motor to
the outside. The ducting can be aluminum or galvanized steel dryer
ducting, or PVC pipe. Over time metal ducting will corrode from the
fumes, but it is inexpensive to replace. For a permanent
installation, you can cut through the outer wall and install an exhaust
duct, like those used on clothes dryers. However significant
improvements in air quality can be obtained by simply running the exhaust
ducting out or under a door. My kiln is on a wheeled stand, so I
hang my ducting on the wall when I am not firing. When I am firing,
I connect the ducting with clamps, and run it out my garage side
door. There is a very noticeable difference in the comfort of my
studio (reduced smell and heat) and the glaze results when I use my vent
vs. when I don't.
Q. Is it hard to drill the holes?
A. No. Most manufacturers will drill the holes for you if you
purchase the vent with your kiln. However, it is also very easy to
do yourself. Kiln brick is so soft that you don't even need a
drill. You just twist the drill bit between your fingers
Q. Won't I waste a lot of energy by pulling the heat away?
A. Actually the amount of air that flows through is not very high, and
very little heat is lost. Kiln manufacturers consider this heat loss
Q. Do I have to order a vent at the
time I order my kiln?
A. No. A vent can be added to any kiln at any time.
Q. How does a Downdraft Vent work?
A. The vents we have been describing are downdraft vents.
Q. What about those vents I see
that hang above a kiln?
A. Those vents (called hoods) remove some, but not all the fumes from the
kiln. They are typically used with gas kilns where downdraft isn't a
Q. Do I need a certain brand of
A. Other than the Cress Clean Air System which requires that the kiln be a
"vent ready" Cress kiln, any brand vent can be used on any brand
Q. Can I vent multiple kilns at