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Selecting the Right Kiln

by Rich and Melodee of Handsnclay

 

Selecting the right kiln can seem like a confusing and daunting task.  After all, you are preparing to purchase a machine the produces inferno-like temperatures in excess of 2,300 degrees Fahrenheit, uses large amperages of 240 Volt AC power, and can be equipped with a programmable firing control.  With all of the different makes, models, sizes, and varieties on the market, how do you choose the one that is best for you?

At Handsnclay, we want to make things simple for you, especially when purchasing your first kiln.  As such, we have written this information guide to selecting your kiln, based upon our personal experiences years ago.

First, don't be intimidated.  Spend as much time as you need educating yourself in kilns.  We recommend that if you are taking pottery or ceramics lessons, that you ask your instructor to see the kilns that are used for your class.  Ask to watch them load, start, and unload the kilns.  Pay special attention to the loading and stacking process.  It is this process that will help you to understand the size of the kiln that you will require.  Remember, the inner dimensions of the kiln are what matter the most when selecting your kiln.

 

Inner Dimensions

Why are knowing the inner dimensions of the kiln so important?  Simply, it is the opening and the depth that gives you the useable volume to fire your pieces.  For example, our most popular kiln, the Excel EX-226 has a 17.5" diameter and an 18" depth.  With an internal depth of 18", you could realistically fire a piece that is 17" tall and 16" wide.  You do not want to load a piece that is as wide or as deep as the kiln itself for a couple reasons.  First, you would have a very difficult time loading and unloading the piece due to the interference you would have with the kiln walls.  You need at least 0.5" of space between the edge of the piece and the kiln walls to be able to load it without damaging the piece.  Second, you want a little space between the kiln walls and the piece you are firing to allow the kiln to transfer heat evenly.  If the piece is touching the kiln walls, the electric elements could produce hot spots on those areas, creating an end product with uneven firing characteristics.  The piece could even break or shatter while firing.

All kilns should be purchased, minimally, with a kiln furniture kit and a variety of stilts.  Kiln furniture kits (Figure 1) are designed specifically for the inner dimensions of your kiln and consist of a variety of ceramic shelves and columns that you can arrange to productively stack your pieces when firing.  When ordering your kiln, request that a Kiln Furniture kit be added to your order.

Figure 1: Kiln Shelf Kit

Stilts (Figure 2) are ceramic shapes and pieces with nail like pins extruding from them.  They are used to rest your pieces on them, atop the shelves in your kiln.  The pointed ends on the stilts give your piece a stable surface to rest upon while it fires, allowing it to be easily removed from the kiln when complete.  If you do not use stilts, your pieces will likely adhere to the shelves or the kiln floor.  Remember, pottery clay, ceramic slip, and glaze are made of glass, and when you fire those materials, the glass can flow and fuse to other surfaces that it comes in contact with.

Figure 2: Assortment of Pointed Stilts

Figure 3 illustrates how one can arrange shelves and stilts within a kiln.  This photo shows the interior of an Excel EX-226.  Notice that at the very bottom of the kiln, a full octagonal shelf is placed.  This bottom shelf is actually resting on four 1" ceramic columns that are part of a typical kiln furniture kit. 

Also notice that roughly 6 inches higher, and resting on taller columns, a half shelf has been placed.  This arrangement is practical for firing a very tall price (like a vase) that can be placed on the bottom shelf.  Smaller pieces can be placed on the upper, half shelf, sharing the firing event.  Notice the tripod or star-like pieces on the half shelf.  Those are stilts (previously discussed) that can be used to place your pieces atop while firing.

Figure 3: Shelves and Stilts in EX-226 Kiln

If you look even more closely, you may be able to see the 0.5" gap between the edges of the shelves and the kiln walls or fire brick.  This gap is necessary for aforementioned reasons.  You can also see the elements that heat to a red hot glow when firing.  Those are the horizontal grey lines in Figure 3.

 

Outer Dimensions

Outer kiln dimensions are only important to consider if you are facing size limitations where you will ultimately install your kiln.  Figure 4 depicts a Skutt KM-818 (similar to Excel EX-226) in the corner of our garage.  Notice the door to the left of the kiln.  This door can be opened slightly while the kiln fires, allowing the fumes the vent.

Figure 4: Skutt KM-818 in Garage

When considering the outer dimensions of your kiln, it is recommended to have at least 2 feet of clear space around the perimeter of the kiln, in all directions.  Remember, these machines can reach over 2,300 degrees F, and the exterior stainless steel jacket gets too hot to touch very quickly. 

Because we like to tuck our Skutt Kiln into the corner of the garage when not it use, we built a small wooden platform (Figure 5) on casters that the kiln rests in.  As you can see, this makes moving this little kiln a very simple task.  We only move the kiln when it is cool, and when the breaker is turned OFF.

Figure 5: Home Built Platform on Casters

 

Electrical Service and Kiln Location

All electric kilns require some heavy duty electricity in order to run properly.  So when you ultimately decide to choose your location for your kiln, you may want to consider placing it in a location that is relatively close to existing electrical service panels, breaker boxes, or existing 240VAC receptacles (used typically for electric ranges, dryers, or even A/C units).  Smaller kilns can be plugged into 240VAC receptacles.  Larger kilns must be direct wired by a certified electrician.  If you have any tough questions about power for your kiln, Rich is an electrical engineer and would be happy to assist you!

Figure 6 shows the plug for our Skutt KM-818, inserted into the appropriately rated, three prong receptacle (dryer type plug).  Figure 7 shows it unplugged.  When we built our home, we decided to have the electrician install a receptacle and dedicated breaker just for the kiln.  In fact, this receptacle is only several inches below our main breaker panel in the garage.

 

Figure 6: Plug for Skutt KM-818 Kiln

 

Figure 7: Plug for Skutt KM-818 Kiln - Unplugged

 

Figure 8 illustrates the main breaker panel that services our home.  The 240VAC breaker on the bottom left of this panel provides dedicated power to the Skutt Kiln in our garage.  This makes it very convenient for us to turn the breaker OFF when the kiln is not in use or when we move or unplug the unit.

Figure 8: Breaker Panel Servicing the Skutt Kiln

 

If your home cannot be modified to connect you kiln in such a manner as we have shown, the smaller kilns can be installed in your utility room (where your electric dryer resides) so long as it can be far away from nearby walls, and, a window is available to be opened while firing.  For applications where natural ventilation is not available, the use of a kiln vent (Figure 9) can be used.  A kiln vent uses an electric blower fan to vent fumes to the outside world, very much like your electric dryer vent.

 

Figure 9: Kiln Vent

Finally, if you are interested in a larger kiln, or have access to 3 phase electrical power (most homes only have single phase), you can purchase 3 phase kilns.  3 phase kilns can be less expensive to purchase and, in many cases, to operate.  However, it is rare that providing 3 phase power to a home would ever be cost effective.

 

What About Cones?

A cone is a piece of material that in the old days, would be installed in a switch on the kiln limit timer to control firing.  It would basically melt when the kiln reached temperature, shutting off the electricity to the kiln in a very crude but reliable manner.  Physical cones are still in use today and many tried and true potters swear by them.  At Handsnclay, we have found that most people prefer not having to mess with cones.  Most of our customers opt for a programmable control (more on this subject later).

Selecting the cone that your kiln will fire to is extremely important, and most people will want a unit that will fire to Cone 10 (2,381 degrees F).  However, in reality, we find that most of our customers rarely fire above Cone 8 (2,320 degrees F).  The Cone is simply the maximum temperature the kiln will reach.  Many high fire clays and glazes must be fired at a minimum cone 6 to 8, and some to cone 10.  We recommend the purchase of at least a cone 8 kiln.

 

Fire Brick

Fire Brick is the ceramic core of your kiln.  It is encased in steel jacketing that holds the electric elements.  Fire brick is typically in 2.5" thick.  However, some kilns have 3" thick brick.  So which one is right for you?

The answer is simple, kilns with 3" brick are slightly more energy efficient than those with 2.5" brick.  Think of it like insulation for your home.  The thicker the insulation, the more efficient the home.  However, the savings from 2.5" to 3" brick is marginal at best.  Also, some claim that a 3" brick cools more slowly, which in theory, it does.  This can create slightly different glaze results.  In practical terms, we have never seen a firing difference in our 2.5" versus 3" kilns.  Though some potters who like to use porcelain clays tend to prefer 3" kilns due to the characteristics of porcelain.

The bottom line is that the dimension of the brick is not a significant factor in practical terms.

 

Controls

With the advent of low cost control electronics, kilns have evolved tremendously over the last ten years. 

Figure 10: Programmable Control

Figure 10 shows a programmable control by Excel called SelectFire.  It can be added to existing kilns of any make or model, or can be ordered on a new kiln.  Once you use such a control, you will throw away your cones forever!  These controls allow you to set them and forget them.  You can also experiment with custom firing profiles and can replicate them with computer precision at any time. 

A kiln with a programmable control may cost a little more initially, but quickly pays for itself as you will no longer need to buy cones.  When you consider the precision and flexibility of the control, the choice becomes obvious.

Remember that all controls are not created equally.  As Rich is an electrical engineer who also repairs kilns and wheels, he has a unique perspective on whose electronic controls are designed and built better.  That is why we only sell certain brands of kilns.  Excel and Skutt have premium quality controls that utilize heavy duty electrical components.  Remember, it is what is on the inside that matters the most!

But in the end, for whatever kiln you decided to purchase, be sure to choose a kiln with a programmable control.

We hope you found our personal experience in buying a kiln for our home to be informative and beneficial to your kiln purchase.  If you have any additional questions, simply email us and we will guide you through the process.  We don't want you to be confused or intimidated when buying your kiln.