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VENTING INFORMATION
Carbon monoxide, chlorine, fluorine, sulfur dioxide, and nitrogen dioxide
fumes are among the most prevalent gases present during a kiln firing,
and can cause nausea, sore throats, fatigue, and headaches. In a 12" x
18" x 9" room (1944 cubic feet), concentrations of carbon monoxide in
a greenware firing at one point reached a level of 300 ppm without ventilation
(from the Kiln Fumes can be Dangerous brochure, by Vent-A-Kiln Corporation).
Proper ventilation is necessary to remove these fumes from your work area.
There are two main types of ventilation - general (or dilution) ventilation,
and local exhaust ventilation. General ventilation follows the principle
that if the hazardous gases are mixed with enough clean, fresh air, they
become dilute, lowering the concentration of the gases. This can be achieved
by room fans or open windows and doors. Local exhaust ventilation uses
a vent system that specifically removes the fumes from the kiln, before
they mix with the air in the room. Some states and school districts require
local exhaust venting systems on kilns. While the average cost for a kiln
vent is $300 to $400, the cost to run a vent is only around 1ยข per hour.
Kiln vents are available in updraft and downdraft styles. The updraft,
or hood vent, utilizes the natural upward flow of fumes and heat. During
a firing, the hood is lowered over the lid of the kiln using an overhead
counterweight pulley system. The spun aluminum hood is compactly designed
to fit easily on top of the closed kiln. Besides reducing fumes, it also
eliminates heat buildup for more comfortable working conditions and reduced
air-conditioning costs.
The downdraft style vent system extracts fumes directly from the kiln,
using small holes drilled in the kiln for that purpose. The holes are
usually 15/64" in diameter, and are drilled in the top and bottom of the
kiln (a drill bit is provided). The fan motor, located either below the
kiln or directly beside the kiln on the floor, draws fresh, oxygen-rich
air from the top of the kiln, through the chamber, and out the base of
the kiln. This promotes more even firing temperatures and more consistent
glaze oxidation results. The lid of the kiln is never propped open, and
the peep holes remain plugged during the entire firing, which reduces
the need to touch the hot kiln.
Either vent system uses standard clothes dryer style ducting and 110
volt (standard household current) electricity, and can easily be installed
by anyone. Visit or call us to discuss which venting system would work
best for your particular situation. There are many options not covered
which may fit your needs better.
"When to vent" is a serious question, and one that is asked frequently.
Schools, institutions, and studios where the kiln is located in the same
area work is performed should almost always be vented. Literature illustrating
the necessity to vent in those situations is available, and we"d be happy
to provide whatever assistance or guidance you might need to convince
school administrators that a vent system is required in your situation.
But if you are a potter who has the kiln in a garage or room that is not
occupied during the firing cycle, a vent system is more often thought
of as a luxury. A vent can always be added, and a vent will always help
remove fumes and in many situations, improve firing results. We encourage
you to at least look into the different venting options and talk with
us about the necessity of venting.
FREQUENTLY ASKED QUESTIONS ABOUT DOWNDRAFT VENTS
Why Vent A Kiln? Venting is important to bring
air into the kiln for successful firings and to remove fumes from your
work area. Downdraft vents do both very well.
Why is it important to have air in the kiln? Clay bodies,
glazes, decals, lusters, etc. need air to fire properly. Many problems
with color, glaze fit, and porcelain mildew occur because of too little
oxygen in the kiln.
What happens to air in the kiln? The products we fire contain
organic materials. These react with oxygen to form carbon monoxide early
in the firing. During firing, the gases in the kiln expand just like air
in a hot air balloon. These gases are forced out through cracks and holes,
making it difficult for new air to enter the kiln.
How does a downdraft vent help my firing? The Orton downdraft
vent pulls fumes out of the kiln, allowing air to enter. Electric kilns
are naturally hotter at the top. With a downdraft vent, hot gases near
the top of the kiln are drawn down, providing better temperature uniformity.
Are there any health and safety issues? Testing has show
that carbon monoxide produced during firing can be higher than accepted
government (OSHA) standards [35 ppm (0.0035%) for continual exposure or
220 ppm for short term exposure]. Carbon monoxide can produce headaches,
fatigue, sore throats, and nausea. Fumes from kilns may also contain organics,
volatile metals, fluorides, and sulphur oxides, which should be removed
from the work area.
What’s the difference between a downdraft and a hood vent?
A downdraft vent is a patented system which removes all fumes and odors
from the kiln while at the same time bringing in air to improve firing
conditions. A hood system does not vent the kiln. It simply removes fumes
that have already entered the room. There are no firing benefits and only
up to 85% of the fumes are removed. Conditions in the kiln are not improved
with hoods.
What are some of the benefits of a downdraft vent?
- Air brought into the kiln replaces carbon monoxide and adds oxygen
needed for best fired results.
- Hot gases are circulated through the kiln, providing more uniform
temperatures.
- Oxygen in the kiln reduces corrosion of metal heating elements, thermocouples,
and Kiln-Sitter® parts, increasing their life.
- Costs less than a penny an hour to operate. It requires 80% less make-up
air than hoods or cooling makeup air as compared to hoods.
- Manual venting is eliminated. No more touching the hot kiln to lower
the lid or replace peephole plugs. The kiln stays closed throughout
the firing and cool-down is quicker (4 - 6 hours less) without opening
the lid.
- Downdraft venting removes essentially all fumes. It does not significantly
increase firing time or affect the ability of the kiln to reach temperature.
- Most kiln manufacturers recommend and sell downdraft venting. It is
easy to install with no overhead pulleys.
DOWNDRAFT VENTING IMPROVES FIRING CONDITIONS IN THE KILN, WHILE REMOVING
FUMES FROM THE KILN AND WORKROOM!
This page was last updated:
Sunday, December 4, 2005 11:56 PM
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