Ceramic Kilns

Where will the kiln be located?

First, you must decide where your kiln is going to be installed. For a school, that might be in the classroom or in the boiler room. In a studio, where space selection is more limited, the size of the available area will help determine the size of the kiln. But the following points remain constant:

• Kilns should be located in a separate, well-ventilated room other than in an immediate work area.
• Never install a kiln on any combustible floor such as wood or carpet.
• The spacing between the kiln and wall must be a minimum of 18" regardless of what room it’s in.
• Measure carefully to make sure the kiln will fit through all doors leading to the placement location. Sectional kilns can be easily taken apart to fit through narrow doorways or staircases.

What power is available at your location?

It is important to check with maintenance personnel or a professional electrician to find out the following electrical information for the destination of placing your kiln.

Voltage — Voltage services can be 120V, 208V, or 240V. "220V" service is a generic term and does not exist in the USA or Canada. Most residences only have 120V and 240V, whereas commercial and institutional buildings may have all three available. It is important to check the voltage available in the area where the kiln will be located as different buildings may have different supplies. Some 240V kiln models will have a higher temperature rating.

Phase — All 208V and 240V service will be either single-phase or three-phase. Nearly all residential service is single-phase, whereas commercial and institutional services may have both available. Single-phase has two current-carrying wires and a ground, and three-phase has three current-carrying wires and a ground. They are both equally efficient. However, three-phase supplies allow for smaller wire and some kiln models designed for three-phase will have higher temperature ratings.

Amps — The kiln size you are considering could determine the amperage supplied to the building. Additional amperage may be added to the location by expanding the existing service. Again, refer to your maintenance personnel or electrician to determine the existing amps that are supplied.

What is the maximum temperature you will require?

It depends on what type of clay and glazes will be fired in the kiln. Whether you use high or low fire clays will help determine the maximum temperature for your needs.

Clay:

• High Fire – Cone 5 (2167°F) and higher
• Low Fire – Cone 05-06 (1828°F-1888°F)

Glazes:

• High Fire – Cone 5 (2167°F) and higher
• Low Fire – Cone 04-05 (1888°F-1945°F)

What is the maximum chamber size required?

The quantity of pieces you want to fire at one time and the size of the artwork being produced must be evaluated to determine maximum chamber size. Keep in mind the volume of work that will need to be fired in busy months.

What safety measures should be taken when firing?

Always be present during the end of the firing cycle and cool down period to prevent over-firing. The kiln surface emits heat. Do not install near combustible surfaces or under a sprinkler head. Do not touch the surface while firing, wait until cooled to 130°F before opening lid and always wear heat-resistant gloves.

What is the recommended procedure for firing with a manual kiln?

• Place the correct jr. cone in the kiln sitter and set the falling weight.
• Set the timer to 30 minutes past the anticipated firing time.
• Prop the lid if the kiln is not equipped with a downdraft vent.
• Turn switches to LOW.
• Two hours later, turn switches to MEDIUM.
• Two hours later, remove the prop with a gloved hand and turn the switches to HIGH.
• The kiln will shut off automatically when the proper heatwork has been achieved.

What are the advantages of an automatic kiln?

An automatic controller allows the user to create precise, repeatable schedules. This provides consistent results, or more creative control when experimenting. Delay and auto shut-off features increase convenience and safety.

Why vent a kiln?

Fumes, odors and vapors are created when clay bodies and glazes are fired. It is important to clear them out of inhabited spaces for the comfort and safety of those around. Additionally, the venting process affects the firing results. A venting hood will dispel most of the fumes as they escape the kiln. Mechanical downdraft systems improve consistent heat distribution and circulation, as well as remove fumes before they can enter the room, or transfer color from one glaze to another inside the kiln.

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 carbon and organics. 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. A downdraft vent system pulls out the fumes, allowing fresh air to enter.

Are there any health and safety issues?

Testing has shown that carbon monoxide produced during firing can be higher than accepted government (OSHA) standards. [35 PPM (0.0035%) for continual exposure or 200 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 vent and a hood?

A downdraft vent removes fumes and odors from the kiln while at the same time bringing in air to improve firing conditions in the kiln. 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 about 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, providing more uniform temperatures.

Oxygen in the kiln reduces corrosion of metal heating elements and kiln sitter parts, increasing their life.

A downdraft vent costs less than two cents per hour to operate. It requires 80% less makeup air than a hood above the kiln and saves up to $1.00 per day for heating or cooling makeup air as compared to a hood.

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 (4–10 hours less) without opening the lid.

Downdraft venting is much more effective than a hood in removing 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 easily installed with no overhead pulleys.

Note: Only downdraft venting improves firing conditions in the kiln, while removing fumes from the kiln and workroom!