What Is a Kiln Sitter and How Does It Work?

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If you’re buying or using an older pottery kiln, you may come across a piece of equipment called a kiln sitter. If you’ve only used modern digital kilns, the kiln sitter can look confusing at first.

So, what is a kiln sitter, and how does it work?

A kiln sitter is a mechanical device found on many older electric pottery kilns. It is designed to help shut the kiln off when a specific amount of heatwork has been reached, using a small pyrometric cone or cone-shaped device.

Understanding how a kiln sitter works can be especially helpful if you’re considering buying a used pottery kiln or learning to operate an older model.

What Is a Kiln Sitter?

A kiln sitter is a mechanical temperature-control and shutoff system used on certain older electric kilns.

Instead of relying on a modern digital controller to monitor the firing, the kiln sitter uses a small cone positioned inside the kiln.

As the kiln heats, the cone gradually bends. When it reaches the intended position, it activates a mechanical mechanism that shuts the kiln off.

This gives the potter a relatively simple way to control the end of a firing.

How Does a Kiln Sitter Work?

The basic idea is fairly simple.

A small pyrometric cone is placed inside the kiln sitter mechanism. As the kiln heats, the cone responds to the heatwork inside the kiln.

When the cone bends sufficiently, it releases or moves a sensing rod. That movement activates the kiln sitter’s shutoff mechanism.

The kiln then stops heating.

In simple terms:

Kiln heats → cone bends → mechanism activates → kiln shuts off.

The exact design varies between kiln models, so always follow the instructions for the specific kiln sitter installed on your kiln.

What Is the Cone in a Kiln Sitter?

The cone used with a kiln sitter is a specially designed pyrometric device.

Unlike an ordinary thermometer, a cone responds to heatwork, meaning the combined effect of temperature and time.

Different cones are designed to bend at different heatwork levels.

The correct cone depends on the type of firing you’re doing and the manufacturer’s recommendations.

Using the wrong cone can cause the kiln to shut off at an inappropriate point in the firing.

Kiln Sitter vs. Digital Kiln Controller

Modern kilns often use digital controllers that allow potters to program detailed firing schedules.

A kiln sitter is much more mechanical.

A digital controller can manage heating rates, target temperatures, hold times, and multiple stages of a firing.

A kiln sitter primarily provides a mechanical shutoff based on the movement of a cone.

That doesn’t necessarily mean an older kiln is unusable. Many older kilns can still produce excellent pottery when they’re properly maintained and operated according to their specifications.

Why Do Older Pottery Kilns Use Kiln Sitters?

Kiln sitters became popular because they provided a practical way to automate the end of a firing without requiring modern electronic controllers.

They were particularly useful for potters who wanted the kiln to shut off automatically after reaching a predetermined amount of heatwork.

You may still encounter kiln sitters today when buying older or used pottery kilns.

What Are the Advantages of a Kiln Sitter?

One advantage is its relatively simple mechanical design.

A kiln sitter doesn’t require the same type of digital programming found on modern controllers.

It also uses a pyrometric cone, which responds to heatwork rather than simply displaying the air temperature.

For someone using an older kiln, learning how the kiln sitter works can make the firing process much easier to understand.

What Are the Limitations of a Kiln Sitter?

A kiln sitter is not the same as a modern programmable controller.

It generally doesn’t provide the same level of control over heating rates, holds, or multi-stage firing schedules.

The mechanism also needs to be correctly adjusted and maintained.

Because it is a mechanical safety and control device, you shouldn’t assume that an old kiln sitter will work correctly simply because the kiln powers on.

Can a Kiln Sitter Fail?

Like any mechanical component, a kiln sitter can eventually wear out or become unreliable.

Problems can involve the cone support, sensing rod, shutoff mechanism, electrical components, or adjustment of the mechanism.

If you’re purchasing a used kiln with a kiln sitter, inspect the system carefully and find out whether it has been maintained.

If you’re unsure whether the kiln sitter is functioning correctly, have the kiln inspected by someone qualified to work on pottery kilns.

What Should You Check When Buying a Used Kiln With a Kiln Sitter?

If you’re considering an older kiln, don’t just look at the kiln’s exterior.

Ask the seller:

• Does the kiln sitter work properly?
• When was it last serviced?
• What cone does the kiln use?
• Are replacement parts available?
• Have the heating elements been replaced?
• What temperatures was the kiln normally fired to?
• Does the kiln reach its intended temperature?
• Is the electrical system in good condition?

You should also inspect the kiln bricks, heating elements, lid, wiring, controller or switches, and other major components.

Is a Kiln Sitter Accurate?

A kiln sitter can provide useful control when properly installed, adjusted, and operated with the appropriate cone.

However, it should not be treated as an excuse to ignore the firing.

Potters can use witness cones inside the kiln to visually check the heatwork received by the firing.

This can be particularly helpful when learning an older kiln or troubleshooting firing results.

What Are Witness Cones?

Witness cones are pyrometric cones placed inside the kiln where they can be observed after or during the firing.

They provide a visual record of the heatwork experienced at different locations in the kiln.

For example, if cones in different parts of the kiln bend differently, it can provide clues about temperature variation throughout the kiln.

Witness cones can therefore be useful even when a kiln has a kiln sitter.

Is a Kiln Sitter Safe?

A properly maintained kiln sitter can be an important part of an older kiln’s control system, but it should never be treated as a replacement for proper kiln safety.

The kiln should be installed correctly, operated according to the manufacturer’s instructions, and regularly inspected.

Electrical repairs and modifications should be handled by a qualified professional.

If a kiln sitter behaves unexpectedly or fails to shut the kiln off correctly, stop using the kiln until the problem has been properly addressed.

Final Thoughts: What Is a Kiln Sitter?

A kiln sitter is a mechanical device used on many older pottery kilns to help control the end of a firing.

It works by using a pyrometric cone that bends as the kiln reaches the required heatwork. Once the cone reaches the designed position, the mechanism activates and shuts the kiln off.

While kiln sitters are older technology compared with today’s digital controllers, they can still be found on used pottery kilns and can be useful when properly maintained.

If you’re considering buying an older kiln, understanding the kiln sitter is an important part of knowing what you’re purchasing. Check its condition, learn which cone it uses, inspect the rest of the kiln, and make sure replacement parts and qualified service are available when needed.