Energy calculator

How much does it cost to fire a kiln?

Cost per firing is energy per firing multiplied by your fuel price, and the energy has three parts. First, heating the kiln itself: brick and fibre have mass, and taking that mass from room temperature to cone 6 absorbs a large amount of energy that you never get back. Second, heating the ware and the shelves. Third, the heat leaking out through the walls for the whole length of the firing.

That third part is the only one most calculators model, which is why their numbers come out low. The steady-state loss is what it takes to hold temperature, and a firing spends most of its hours climbing, not holding. This tool integrates the loss across the ramp, adds the thermal mass of the wall you specified and of the load you entered, and divides by the efficiency of your heat source.

For a typical studio electric kiln, expect single-digit to low-double-digit kilowatt hours for a small test kiln and several tens of kilowatt hours for a full cone 6 firing in a 7 to 10 cubic foot chamber. Enter your own tariff to get the actual figure, because electricity prices vary more between regions than kilns do between designs.

How much power does an electric kiln need?

There is no single correct answer, so the tool shows you four and lets you compare them. The physics minimum is the steady-state loss plus a margin, and it is always lower than what anyone actually builds, because a kiln sized to its heat loss would take days to climb. Real sizing rules are empirical: Olsen's roughly 1 to 1.2 watts per cubic inch of chamber, the same by surface area at 5 to 7 watts per square inch, and the medians from a survey of 60 commercial electric kilns.

The recommendation the tool gives you sits between the practical minimum (about three times the steady-state loss) and the lowest of the industry rules. It also converts that to amps at 240 V, which is usually the number that decides the project, because the supply you can get to the kiln is a harder constraint than anything else on this page.

How much insulation does a kiln need?

Insulation is where the cost per firing is actually won, and the returns fall off fast. Going from 2.5 to 4.5 inches of insulating brick cuts the loss sharply. Going from 6.5 to 9 inches barely moves it, and you have paid for a lot of brick and a much heavier kiln.

R-value alone will mislead you here, for two reasons the tool handles explicitly. Conductivity is not constant: insulating firebrick conducts roughly twice as much heat at 1260 °C as at 260 °C, so a wall rated on a room-temperature figure looks far better than it performs. And a thick wall on a small chamber does not conduct like a flat slab, because the heat-flow area grows from the inside face to the outside. The solver uses conductivity at each layer's own mean temperature, and counts the thick wall either by mean area or by Langmuir's furnace shape factors, your choice, with the other method's figure shown alongside.

Watch the exterior shell temperature as well as the loss. Above about 70 °C the outside of the kiln is a burn hazard, which is an insulation problem before it is a fuel problem.

Electric, gas or wood: how do the numbers compare?

The chamber loses the same heat whatever is heating it. What changes is how much fuel you have to burn to deliver that heat, and it changes a lot. Electric resistance puts essentially all of its input into the chamber. A studio gas or propane burner delivers about half, the rest leaving up the flue. Wood is nearer a fifth, which is why wood firings consume quantities that surprise people coming from an electric kiln.

Gas kilns are sized on burner capacity rather than on heat loss. Olsen's rule is 10,000 BTU per cubic foot per hour for insulating brick, and 16,000 to 19,000 for hard brick, which is capacity at full turn-up rather than what you burn while cruising. Wood is scaled from Olsen's fastfire: about a quarter cord per 18 cubic feet to cone 10.