Steel vs Stone Preheat Times

The table

Why conduction is not the bottleneck

The instinct is that steel conducts heat 30-odd times better than cordierite, so it must heat up faster. The reason that does not follow is the Biot number: the ratio of resistance to heat moving inside a body against resistance to heat crossing into it.

Below about 0.1, internal conduction is effectively free and the whole slab can be treated as one temperature. For the quarter-inch steel here the Biot number is 0.001. Even the worst case on this site - a thick cordierite stone - comes in around 0.09.

So conductivity, the property steel wins on overwhelmingly, is not the limiting factor for any of these. What limits them is how much heat has to go in, which is mass times specific heat capacity, divided by how fast it can cross the surface.

The model, in full

Lumped capacitance. The time constant is:

tau = m x cp / (h x A)

where m is mass, cp is specific heat capacity, h is the effective surface heat transfer coefficient and A is the exposed area. After one tau the surface has closed 63 percent of the gap to oven temperature; after 3 tau, 95 percent; after 4.6 tau, 99 percent.

Worked example - Baking Steel Original. Published mass 15 lb = 6.80 kg. Carbon steel cp = 470 J/kg.K. The plate is 16 by 14 inches, so two faces plus edges give 0.299 m2 of exposed area. With h = 20 W/m2.K: tau = 6.80 x 470 / (20 x 0.299) = 534 s = 8.9 minutes. 3 tau = 27 minutes. 4.6 tau = 41 minutes.

The one input that is an assumption rather than a published constant is h. We use 20 W/m2.K: a linearized radiative component near 21 for a 0.9-emissivity surface warming toward a 500 F cabinet, plus a few W/m2.K of still-air convection. Take h as 30 and every time above shortens by about a third.

The cross-check that makes us believe it

Baking Steel publish their own preheat guidance for the Original: 45 to 60 minutes at 500 to 550 F. Our model, built entirely from their published mass and a textbook specific heat capacity, gives 41 minutes to 99 percent.

Two completely independent routes landing on the same answer is the strongest validation available to a site that owns none of this equipment. It is also why we trust the model on the plates whose makers publish no guidance at all.

What this means in the kitchen

Do not shorten the preheat because you bought a steel. If anything, lengthen it.

Thickness costs preheat roughly in proportion to mass. Going from a quarter inch to three eighths adds about 15 minutes; to a half inch, about 28.

The way to know is to measure. Every figure above is a model with an assumed h. A twenty-dollar infrared thermometer replaces all of it with a number from your own oven, and that is the honest recommendation this whole page leads to.