Types of Kilns: An Informative Guide for Kiln Users

Kilns have been used for millennia to create ceramic, glass, and even metal objects. As technology has advanced, so have kilns. Now, there are a wide variety of kilns available on the market for hobbyists and professionals alike. In this guide, we’ll explore the different types of kilns and their specific uses.

What Is a Kiln?

Before getting into the distinctions between the different types of kilns, let’s reach a broad definition for what a kiln is. A kiln is an insulated chamber that can be heated to very high temperatures for firing, burning, or drying of pottery, ceramics, glass, metals, or other materials.

Types of Kilns: Overview

As human civilization has evolved, the kiln has undergone many iterations. There are multiple ways to categorize kilns. For instance, you can categorize kilns based on power source, heat distribution, structure or technique, use-case or size, material fired, or control method. Below is a quick overview of the various types of kilns. Later in the article, we’ll be exploring the most common types of modern kilns more in-depth.

Types of Kilns Based on Power Source

• Wood-Fired Kilns: Wood-fired kilns use heat from burning wood to increase the temperature of the kiln.
• Coal-Fired Kilns: Coal-fired kilns, which used coal to replace wood for the fuel source, were widely used up until in the mid-twentieth century.
• Gas Kilns: Gas kilns use natural gases or propane to heat materials and are capable of reaching high temperatures that exceed the temperatures of wood burning or electric kilns.
• Electric Kilns: The most common type of kiln for artists and hobbyists, electric kilns use electric current to heat elements inside the kiln, offering more precise control over temperature.

Types of Kilns Based on Heat Distribution 

• Intermittent Kilns: Intermittent, or periodic, kilns are only heated some of the time. With intermittent kilns, the ware is placed inside the kiln and the internal temperature of the kiln is increased or decreased based on a firing schedule. However, once the firing is complete, the ware and the kiln itself are allowed to fully cool.
• Continuous Kilns: Continuous kilns are perpetually heated. Continuous kilns, or tunnel kilns, have a continuous heat source in the center. Ware is physically moved throughout the kiln, closer or farther to the heat source, to control its temperature. Continuous kilns are more commonly used for industrial processes.
• Updraft Kilns: Updraft kilns are heated from the bottom of kiln and air is exhausted from the top.
• Downdraft Kilns: More efficient than updraft kilns, downdraft kilns are also heated from the bottom, but the construction of downdraft kilns forces the hot air to recirculate the kiln rather than escaping from the top.

Types of Kilns Based on Structure or Technique

• Pit Fire Kilns: The earliest iteration of the kiln, pit fire kilns are wood burning kilns that rely on earthen pits to provide insulation.

• Beehive Kilns: Beehive kilns, another early iteration of wood burning kilns, utilize arches to create a domed brick chamber for firing. Beehive kilns included baffles to regulate airflow and control the temperature of kiln, as well as holes at the top of the chamber (and later chimneys) to allow the heat to rise.

• Climbing Kilns: Climbing kilns were built into hillsides. A fire would be lit at the bottom and, since heat rises, the temperature of the kiln would increase with greater regularity, allowing for greater quantities of pottery to be fired.

• Soda Kilns: Soda kilns use large, arched chambers, with a chimney on one end, and are heated to high temperatures. During firing, sodium bicarbonate dissolved in water is sprayed onto the ware to form a glaze.
• Sawdust Kilns: Sawdust kilns are simplistic kilns that consist of a small brick chamber where bisque is covered in sawdust. A grate is used to cover the top of the kiln, and the fire is lit on top of the grate.
• Anagama Kilns: Originally invented in China and later brought to Japan, Anagama kilns are wood-burning kilns that consist of a sloped earthen structure with a single fire chamber on one end and a chimney on the other.
• Noborigama Kilns: An evolution of the Anagama kiln, Noborigama kilns are multi-chambered wood-fired kilns that consist of a succession of chambers with a stoked fire at the lowest level. More efficient than Anagama kilns, Noborigama kilns capture and recirculate the hot air from previous firings.
• Raku Kilns: Raku is a firing technique where the ware is removed from the kiln while the kiln is still hot. As such, Raku kilns must allow for the ware to be easily removed. Today, most Raku kilns are gas powered since electric kilns can be damaged by opening them when the kiln is at temperature.
• Top Hat Kilns: Top hat kilns are designed so that the firing chamber is lowered down onto the wares and then raised again when firing is complete, often using a hand-crank.
• Bottle Kilns: An evolution of the beehive kiln, bottle kilns (or bottle ovens) are coal-fired kilns made from brick that consist of a hovel that tapers into distinctive bottle-shaped chimney – hence the name! The unique shape of the bottle kiln improved draught while protecting wares from inclement weather.

• Car Kilns: Typically used for industrial processes, car kilns utilize a static firing chamber, through which wares are moved on a wheeled cart. Smaller scale car kilns are occasionally used by schools or potteries.
• Front-Loading Kilns: Front-loading kilns, or side-loading kilns, have a hinged door built into the front of the kiln. Wares are loaded horizontally into the kiln.
• Top-Loading Kilns: Top-loading kilns have a hinged door built onto the top of the kiln. Wares are lowered down into the kiln, making it easier to ensure they’re centered.

Types of Kilns Based on Material Fired

• Glass Kilns: Glass kilns are specifically designed to heat glass to very precise temperatures so it can be fused, slumped, or cast.
  • • Annealing Kilns: Annealing kilns are used to slowly cool down glass to improve its durability and prevent the glass from experiencing thermal shock.
• Ceramic Kilns: Ceramic kilns, or pottery kilns, are used to fire pottery, clay, and other ceramic materials.
• Knife Kilns: Knife kilns, also commonly referred to as heat treat ovens, are designed to heat treat blades to increase their hardness, improve their durability, or otherwise alter their physical properties.

Types of Kilns Based on Use-Case

• Hobby Kilns: Hobby kilns tend to be smaller and less expensive, intended for home or studio use by artists and crafters. Depending on their size and design, hobby kilns can be used for a variety of applications, ranging from firing single quantities of small ceramics and glassware to firing small batches of wares or more large-scale pieces.
• Industrials Kilns: Industrial kilns are much larger and more powerful, designed to handle large quantities of materials in industrial settings. Designed for production and commercial use, industrial kilns are used to fire larger quantities of materials or for processes that require higher temperatures.
• Small Kilns: Small kilns are small, transportable kilns, for firing a small quantity of material. They are typically used by hobbyists who work in a home or studio setting and have limited space. Typically ranging between .6 and 6 cubic feet, small kilns can be used for a variety of applications, such as making jewelry and small ceramic pieces to slightly larger wares.

• Large Kilns: Large kilns are large, often permanently installed, kilns that are designed for industrial or commercial use and can handle much larger quantities of materials. Typically larger than 9 cubic feet, large kilns can be used to accommodate a much wider range of applications.

Types of Kilns Based on Control Method

• Automatic Kilns: Automatic kilns, or digital kilns, use automatic temperature controllers to execute the firing process and control the temperature of the kiln without user input.
• Manual Kilns: Manual kilns rely completely on user input in order to execute a firing schedule, although they may sometimes utilize a device known as a kiln sitter to power off the kiln when it’s reached a specific temperature.

Traditional Kilns: The Evolution of Wood Burning Kilns 

The first kilns, developed nearly 10,000 years ago, were extremely rudimentary. They consisted of a hole or trench that was dug into the ground and filled with combustible materials. Pottery was stacked within the flames, and the insulation of the earth allowed the pottery to reach high enough temperatures to fire. This technique, known as pit firing, was extremely sporadic and unpredictable, often resulting in shards of broken pottery.

Wood burning kilns and, later, coal burning kilns, remained the standard up until the industrial revolution. However, over the centuries, technology for wood burning kilns continued to evolve, resulting in greater precision and temperature control. Pre-industrial advancements in kiln technology include beehive kilns, climbing kilns, soda kilns, sawdust kilns, bottle kilns, car kilns, and Anagama kilns – all of which leverage changes in elevation, airflow, and distance from the heat source to better regulate kiln temperature.

Comparisons of Modern Kilns 

While a few contemporary artists and specialists still use wood-fired kilns and traditional firing methods, the industrial revolution introduced the modern kiln, which uses gas or electricity to produce heat. Modern kilns come in a variety of configurations for a variety of applications – from large industrial kilns that are big enough to fill a room to tabletop kilns that are about the size of a toaster oven!

Hobby Kilns vs. Industrial Kilns

The first major distinction between types of kilns is whether they are designed for hobby or industrial use. Hobby kilns tend to be smaller and less expensive than industrial kilns (typically ranging from $700-$2,000 dollars), intended for home or studio use by artists and crafters. These kilns are often electric and digital, making them easy to use and control.

In contrast, industrial kilns are much larger and more powerful, designed to handle large quantities of materials in industrial settings. Industrial kilns can cost tens of thousands or even hundreds of thousands of dollars! Industrial kilns can be electric or gas-powered and may have more complex controls. These kilns play a crucial role in many manufacturing processes and are essential for producing a wide range of products that we use every day.

Small Kilns vs. Large Kilns – Is There a Difference in Performance?

Small kilns vs big kilns…it’s all relative, right?! For this case, let’s think of small kilns as being used by hobbyists who work in a home or studio setting and have limited space. These kilns are typically designed to fire a small quantity of materials at a time and can be easily transported. Big kilns, on the other hand, are designed for industrial use and can handle much larger quantities of materials. They are often permanently installed and require a dedicated space.

But to answer your question – yes. Kiln size can affect performance in several ways:

• Temperature Distribution: Large kilns may have more difficulty maintaining a consistent temperature throughout the entire kiln due to increased heat loss from the larger surface area. This can lead to uneven firing, resulting in variations in color and texture of the fired pieces.
• Fuel Consumption: Large kilns require more fuel to maintain the desired temperature, which can increase operating costs.
• Production Capacity: The size of the kiln will determine the maximum size and number of pieces that can be fired at one time, which can impact production capacity.
• Heat-Up and Cooling Times: Large kilns may take longer to heat up and cool down than a small kiln, which can affect the overall time it takes to complete a firing cycle.
• Maintenance: Large kilns may require more frequent maintenance and repair than small kilns due to the increased wear and tear on the components.

Overall, the size of the kiln is an important factor to consider when determining the performance of a kiln. The optimal size of the kiln will depend on the specific needs and requirements of the user.

Gas Kilns vs. Electric Kilns

When it comes to modern kilns, another big distinction is the power source.

Gas kilns use natural gas or propane to heat the materials being fired. These kilns are often used by industrial manufacturers who need to fire large quantities of materials quickly. Gas kilns can reach higher temperatures than electric kilns, making them ideal for certain types of projects.

Electric kilns, on the other hand, use electricity to heat the materials being fired. They are often used by hobbyists and artists who need more control over the firing process. Electric kilns are typically smaller and more affordable than gas kilns, making them a popular choice for home use.

Manual Kilns vs. Digital Kilns

When using a manual kiln, the operator must manually control the temperature and other variables during the firing process, rather than relying on automated controls. This can involve adjusting the fuel source, opening and closing vents, and monitoring the temperature with a thermometer. Manual kilns are often used by artists and craftspeople who prefer a hands-on approach.

Digital kilns, on the other hand, use a programmable digital controller to automatically carry out the firing schedule without direct user input. Modern digital controllers, such as TAP Controllers from SDS Industries, are fine-tuned, intuitive, and provide constant communication and feedback to users. The controllers allow for precise temperature control and can be programmed to follow specific firing schedules.

Differences between Glass Kilns, Ceramic Kilns, and Knife Making Kilns

Different types of kilns are optimized for specific materials. Glass kilns, ceramic kilns, and knife making kilns are made to meet the unique properties of each of these materials and the way they react to heat. Here are some of the main differences in these kiln types:

Temperature Range

• Glass kilns are typically used for melting and shaping glass at temperatures ranging from 1,1000 to 1,800 degrees Fahrenheit.
• Ceramic kilns are used for firing ceramics at temperatures ranging from 1,800 to 2,400 degrees Fahrenheit.
• Knife making kilns are used for heat-treating steel at temperatures ranging from 1,500 to 2,200 degrees Fahrenheit.

Heating Elements

• Glass kilns often use heating elements made from molybdenum wire.
• Ceramic kilns often use heating elements made from Kanthal wire.
• Knife making kilns may use heating elements made from Kanthal or nichrome wire.

Firing Cycles

• Glass kilns may have longer firing cycles with slow heating and cooling rates.
• Ceramic kilns may have shorter firing cycles with faster heating and cooling rates.
• Knife making kilns may have a shorter firing cycle but a longer hold time at the peak temperature to allow for the desired heat treatment of the steel.

Firing Environment

• Glass kilns often use a controlled atmosphere to prevent oxidation and maintain consistent heating.
• Ceramic kilns may use a reduction atmosphere to enhance the glaze or surface finish of the fired ceramic.
• Knife making kilns may have an inert atmosphere to prevent oxidation of the steel.

Size and Shape

• Glass kilns come in all shapes and sizes, from small, table-top units to large, elongated kilns.
• Ceramic kilns also come in a variety of shapes and sizes but are typically more cylindrical, since you can stack ceramic during the firing process.
• Knife making kilns may be smaller and have a long, narrow shape to accommodate blades or other small metal objects.

Conclusion

There you have it! Like we mentioned in the beginning, the kiln has undergone many different iterations throughout its history, but hopefully now you have a better understanding of the different types of kilns.

If you’re in the market for a new kiln, we encourage you to check out the kilns available at one of our partners:

• Evenheat
• Hot Shot Oven & Kiln
• Mobile Glassblowing Studios, LLC
• Jen-Ken Kilns
• Kiln Frog
• Sheffield Pottery
• Delphi Glass

And if you’re looking for the most advanced, precise, and easy-to-use automatic kiln controllers to pair with your electric kiln, we invite you to check out the TAP and TAP II Controllers by SDS Industries! With responsive touchscreen controls, an intuitive graphical UI, and integration with the TAP Kiln Controller Mobile App, TAP Kiln Controllers are the most advanced, precise, and easy-to-use automatic kiln controllers on the market today. TAP Controllers can pair with any relay-controlled kiln to help streamline the firing process and give you greater control over your projects.

We invite you to explore our selection of automatic kiln controllers, standalones, and conversion kits on our online store.