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making kilns legal (or illegal)

updated mon 24 sep 07


Donovan Palmquist on sun 23 sep 07

I have been reading the thread on "making kilns legal" and feel I need to add to the discussion.

If you do your homework and jump through the right hoops you can set up a safe legal kiln.
If you get proper advice and keep all the officials (as necessary) in the loop you will find that the
process is relatively painless. But you have to know what you're doing...being able to 'speak the
language' with the inspector is key. The reason why most people build 'clandestine' kilns is
because they are afraid of their inspector. Most inspectors don't know anything about kilns so they
cover their butts by sometimes being militant and unreasonable. But that is by far the exception
not the rule.
One inspector actually asked me if there was a 'fireproof liner' inside the kiln.

I have built kilns in 33 states, and the prevailing theme is about making it safe which would then
make it legal. Codes are written to make operation of your kiln safe for you and everyone around
it. This can matter greatly, such as a school or art center or a little less if it's your own kiln in the
middle of nowhere.

According to Uniform Mechanical code, kilns are rated as if they were boilers, constantly on with
very little supervision. There is a section on "hobby kilns" that is antiquated and only somewhat
That portion of the code was written for updraft kilns 20 cubic feet or less and a rating of less
than 399,000btu's input. If you have a kiln under 20 cubic feet you will have fewer restrictions.
When you have a kiln that requires over 400,000btu's you need more safety equipment, and when
you are above 800,000 you need even more.
The "patio kiln" in recent posts sounds perfectly legal, it is way under 400,000btu and has a baso
safety valve and pilot. What might make this kiln questionable in an inspectors mind is the
placement of the kiln. Is it too close to the building?, how far from open windows?
What could burn in the vicinity? I've had inspectors make a school remove ALL wooden ware racks
from a kiln room. Most inspectors are concerned about the liabilities incurred when you install a
kiln in a specific space.
Here are some of the major concerns I have encountered over the last 25 years of dealing with kiln
1. What kind of chimney are you using- UL listed? If you put your kiln in a building on your
property how will your homeowners insurance be affected. This is the #1 question from
inspectors. A well-constructed brick chimney is fine if you have the proper clearances.
2. If the kiln is indoors where is the combustion air coming from and what kind of ventilation do
you have for exhaust. This ties for #1 in the inspectors mind. Carbon monoxide as we all know is
a very insidious gas. An open window does not meet the requirements of "makeup air". I built a
kiln a few years back at a school that had its kiln shut down because because of the near death of
a student. Their makeup air was an open set of windows. It was January and she was cold and
working late in the studio. She shut the windows and nearly died as a result.
Outdoor kilns in their own shed pose less of a problem, my shed for instance is a round metal
grain bin. It is far enough from my studio to be safe and It will not burn. It is not covered by my
homeowners insurance. My propane company made sure my safeties were installed properly
because they do not want the liability of me being injured or killed.
3. Does the kiln have a safety system? Don't cut corners here. All of the gas kilns I build have
safety systems, either Baso switches, flame rod, or UV sensors. Baso pilot switches are the most
inexpensive and easiest to repair and work well in kilns under 400,000btu's. Flame rods w/
electronic ignition also work well in this range and can be used in all kilns up to 800,000btu's.
These are more expensive but work well if properly maintained. UV sensors also work but are very
expensive and are rated to work in ambient temperatures of only 270 degrees. (the temp by the
burner, not in the kiln). On forced air kilns additional air proving switches and centrifugal
switches are used in case there is a loss of power. In addition to all the flame monitoring stuff you
may also need a high limit shutoff. That is for those who fall asleep while firing, forget the kiln is
on or get delayed somhow in getting back to the kiln. It also doubles as a pyrometer. In some
cases a stack temperature sensor is needed but that is rare.
4. Clearances.....from combustables, from open windows, from neighbors. This is self
explanatory. Faulty assumptions about clearances cause most kiln fires. Having the right chimney
improperly flashed through the roof is the #1 cause of kiln building fires. The more space around
the kiln the better, however sometimes that is difficult and you must make yourself aware of the
clearances and pay attention to them.
These are by far the most asked questions and the biggest concern for inspectors. Trying to "fly
under the radar" is no longer acceptable in most cases. I am old enough to remember and still see
stealth kilns running on high pressure propane with no safeties. This was how we did it. Some of
you know this type of kiln and some of you had accidental haircuts and exploded kilns as a result
of flying by the seat of your pants. A propane kiln is just about a bomb when safeties are
compromised. I have seen it all and don't wish to see it anymore. I have many stories of foolish
shortcuts potters have taken that fortunately have not killed anyone.

The bottom line is to use common sense with the input of an expert. If you have to ask the
questions you probably need help in setting up a kiln. Don't guess. If you are a risk taker and
don't really care about those around you, be prepared to suffer the consequences of a poorly
installed kiln.