A kiln sitter is the mechanical device that turns off a manual electric kiln when a small cone bends. It does not read temperature or run a program. It responds to heatwork, the combined effect of time and temperature that matures clay and glaze, and trips a switch at the end. This guide covers how a kiln sitter works, which cones and bars it takes, setting and calibrating it, common problems, and pairing it with a digital controller. It is research-based: we compare maker manuals and published guides; we do not fire kilns.
What a kiln sitter is, and who makes it
Kiln Sitter (also written KilnSitter) is a trademarked name. For decades W.P. Dawson, Inc. of Brea, California made it, and Dawson-branded sitters appear on many older kilns. In early 2009 Skutt acquired Dawson's KilnSitter division, which Skutt says gave it exclusive rights to the device and its parts.
Orton does not build the sitter. It makes the small cones and bars the sitter uses, and its controller guides explain how to keep a sitter as a backup. Skutt still presents a KilnSitter (KS) line of manual kilns next to its digital KilnMaster kilns.
How a kiln sitter works
The sitter is a lever system that runs through the kiln wall. Dawson's LT-3 and LT-3K booklet names these parts:
- Cone supports: two metal supports inside the kiln that hold the cone or bar.
- Sensing rod and tube: the rod rests on the cone and moves inside a tube through the wall.
- Claw, trigger and weight: outside the kiln, the claw holds the trigger, which holds a weight up.
- Plunger button: pushed in to start the kiln; when the weight drops, the switch opens.
- Limit timer: a backup timer that trips the switch if the cone never does.
The firing sequence is simple:
- The cone lies flat across both supports, and the sensing rod rests on its middle.
- Outside, the rod's other end holds the claw against the trigger, so the weight stays up and the kiln can run.
- As the kiln reaches the cone's rated heatwork, the cone softens and sags between the supports.
- The rod drops with it. That lifts the claw off the trigger, the weight swings down and the kiln switches off.
Because the sitter only switches the kiln off, you control the heating rate by turning the switches up in steps (low, medium, high) at intervals you choose, as Skutt describes for its KilnSitter kilns.
Small cones or bars: what goes in a kiln sitter
A kiln sitter takes small cones (often called junior cones) or pyrometric bars, never the large or self-supporting cones you set on a shelf. Orton describes its small cones as the cones "commonly used in the Kiln-Sitter" and its bars as "specifically designed to function in the Kiln-Sitter." Orton states that bars have the same temperature equivalents as small cones, so a cone 6 bar and a cone 6 small cone should shut the kiln off at the same point.
| Option | Shape | What Orton says | Good for |
|---|---|---|---|
| Small cone | Tapered, about 15/16 in long | The taper lets you shift shut-off by placing a thinner or thicker part under the rod | Fine adjustment once you know your kiln |
| Pyrometric bar | Uniform bar | Uniform shape makes consistent placement easy; same equivalents as small cones | Beginners who want repeatable placement |
Orton sells both in boxes of 50. Pick the cone number your clay and glaze call for: the bisque cone your clay maker suggests, and the glaze's stated cone for glaze firings. Our bisque firing guide and glaze firing guide cover the cone choices, and the pottery cone chart lists temperatures. Orton publishes separate temperature columns for small cones, so do not read a small cone's value from the self-supporting column.
Sitter cones: Orton small cones (cone 6). Shelf witness cones: Orton self-supporting cones.
How to set a kiln sitter before a firing
Set the cone with the kiln switched off. Dawson's booklet describes this routine:
- Clean the cone supports with a small wire brush after every firing; rotate or replace supports that keep residue. Dawson suggests keeping a spare pair.
- Hold the claw down against the trigger so the sensing rod lifts clear of the supports.
- Lay the small cone or bar flat across both supports, against the metal step, centered under the rod. Dawson's diagram places the cone so the inside edge of its number circle lines up with the outside edge of the support.
- Lower the rod gently onto the cone and check that nothing touches the rod, the cone or the tube. Dawson asks for shelves and ware to sit at least 1 inch from the tube.
- Set the limit timer. Dawson says 1/4 to 1/2 hour beyond your estimated firing time (use 1/2 hour until you know the kiln), and never more than 20 hours. Set it before you push the plunger; the plunger will not engage with the timer at OFF.
- Push in the plunger button so the weight latches up, then start turning the switches up as your kiln manual and firing plan describe.
Write each firing in a log: cone used, switch times, total hours and what the witness cones showed. With a sitter kiln, that log is what lets you repeat a good firing.
Check every firing with witness cones
A sitter cone only tells you the switch tripped. Dawson recommends witness cones too, set 1 inch above or below the tube:
- Guide cone: one number cooler than the sitter cone. It bends first and tells you shut-off is close.
- Firing cone: the same number as the sitter cone. Its tip should bend down close to the base.
- Guard cone: one number hotter. If it bends at all, the kiln went past the target.
The Ceramics Monthly article on sitter calibration puts it plainly: trust the large witness cones over the small sitter cone. Our pyrometric cones guide explains how to set up and read a cone pack.
Calibrating a kiln sitter with the firing gauge
A kiln sitter comes with a small metal firing gauge. Slipped over the rod and supports, it holds the rod at the angle of a cone bent to about 90 degrees, which is where the kiln should switch off. With the gauge in place you check how the claw meets the trigger and adjust the trigger plate with its set screw.
Sources differ on the exact setting. Dawson's LT-3 and LT-3K booklet specifies a 1/16 inch clearance between the claw tip and the trigger with the gauge fitted. The Ceramics Monthly calibration article describes the trigger plate just touching the bottom of the claw, with no gap. Follow the manual for your kiln and sitter model, and remove the gauge before firing.
Dawson also says to check that the kiln stands level and the rod is centered, and to repeat these checks every 30 firings. Its test uses small cones in an empty kiln: a cone bent to about 90 degrees means the adjustment is right. Ceramics Monthly suggests recalibrating after buying a kiln, after repairs and whenever results drift.
Common kiln sitter problems
| Problem | Likely causes (Dawson booklet) | What to do |
|---|---|---|
| Ware over-fired, guard cone bent | Cone dislodged, cone touching the tube, ware fallen against the tube, cone placed wrong | Check placement and clearances; lower switch settings if the sitter cone is over-bent; keep the limit timer set |
| Kiln shut off too early, firing cone unbent | Trigger set too high, worn rod, cone too low for the kiln's behavior | Recheck adjustment with the gauge; retest with a cone one number hotter |
| Kiln does not shut off | Claw clearance, trigger setting, uneven floor, weight blocked outside the kiln | Switch off by hand, then check every adjustment before the next firing |
| Inconsistent firings | Sensing rod sluggish, not centered, bent or eroded | Have the tube assembly or rod replaced; Dawson says power must be off first |
| Cone stuck to the supports | Glaze or cone residue built up | Wire brush after each firing; rotate or replace supports |
Shuts off early or late
Ceramics Monthly's rule: shuts off early, raise the trigger plate slightly; shuts off late, lower it slightly. Change one thing at a time and confirm with witness cones.
Rod and tube wear
Dawson notes that high-fire use can bend or erode the rod, which throws off the adjustment, and says to leave the top peephole open during firings to extend tube life. Never oil any part of the sitter; the booklet bans lubricants of any kind.
Dawson's 2000 booklet rates the LT-3 and LT-3K for kiln temperatures up to and including cone 8. If your kiln is rated higher, check the kiln maker's manual for what it says about high-fire use of its sitter.
Kiln sitter vs digital controller
A sitter kiln asks more of you: you turn switches up by hand, stay close to the end of the firing, and get no built-in ramp, hold or slow cool. A digital kiln controller runs the whole schedule from a thermocouple reading. The sitter's advantage is simplicity: no circuit boards, cheap parts and a shutoff tied to heatwork. Sitter kilns still fire good pots with a log, witness cones and attention. Our digital kilns page covers kilns sold with controllers.
Pairing a kiln sitter with a digital controller
You can run a sitter kiln from an external controller, and the sitter can stay in place as a backup shutoff. Orton's AutoFire 4000 and AF4X user guides describe the setup for a kiln with manual switches: turn all the dials to their highest settings so the controller does the switching, and place a cone 10 bar under the sitter's sensing rod as a backup that cuts power at high temperatures. Orton adds that its controller is not a safety device, relays can fail in the "on" position, and the kiln should never be left unattended near the end of a firing.
The usual routes are a stand-alone controller box between the wall supply and the kiln (Seattle Pottery Supply lists a wall-mounted Bartlett-based box in 35, 50 and 100 amp versions) or a conversion of the kiln's switch box. Either way the kiln needs a thermocouple; see our kiln thermocouple guide. Have the kiln maker, a kiln technician or a licensed electrician choose and install it, and keep the sitter working as a backup.
Do not wire a controller into a kiln yourself. Digitalfire notes that home-built controllers are not CSA or UL listed, which can affect fire insurance. Have a licensed electrician check the circuit, and use the volts and amps on the kiln's data plate.
Buying a used kiln with a sitter
Used sitter kilns often cost less than digital kilns. Skutt's dating helps: "Old Style" sitter kilns ran from 1954 to 1980, the "A Series" (Dawson-branded sitter, serial starting with A) from 1980 to 1996, then KS models. Check that the rod moves freely and the timer runs, then use the checklist in our kiln for sale guide.
Safety notes
- Dawson states the sitter is not a fail-safe shutoff. Be present at the end of every firing and switch off by hand if it runs over.
- Keep the kiln off wood floors and carpet, with the clearances in your kiln manual.
- Vent the room or fit a vent; see our kiln vent guide.
- Unplug the kiln or switch off the breaker before replacing a tube, rod or supports, as the manuals say.
- Clean dust with a damp cloth or HEPA vacuum, never by dry sweeping; clay and glaze dust contain silica.
What you need
For a sitter kiln you need small cones or bars, witness cones, spare cone supports and the firing gauge. If you want programs instead, compare digital models in our best electric kilns guide.
Sources: W.P. Dawson KILN-SITTER LT-3 and LT-3K operating booklet (2000); Skutt KilnSitter parts price list (Dawson acquisition note) and KilnSitter wiring diagram page; Skutt KilnSitter kiln line and operation pages; Orton Small Cones and Pyrometric Bars pages; Orton AutoFire 4000 and AF4X user guides (October 2018); Ceramics Monthly "Tips and Tools: The Kiln Sitter"; Seattle Pottery Supply Modular Digital Control Box listing; Digitalfire glossary entry on kiln controllers. Specs checked October 2026.