Over the weekend (yeah, it was raining here in Seattle) I ran a little real-world experiment to gauge the heating/cooling efficiency of saucepans of varying composition. I'm interested in sharing the results, and also in finding out if others have run their own similar--perhaps more scientific--experiments.
I had 4 same-diameter (5.75 inches), straight-walled saucepans, one each of tinned copper (3mm), enameled cast iron (3mm Belgique), stainless/copper clad (1 mm Revereware), and monolithic aluminum (1mm mongrel). I put 3C of tapwater in each, and let them all come up to room temp, then put them, in turn, uncovered, onto an electric radiant heat hob of the same diameter, preheated and maxed out on HI.
The times to boil were as follows:
Cast Iron 9:21
SS Clad 12:10
This order of finish was not surprising to me given the published conductivity numbers of the various metals, but the time differences were surprising--what those differences mean not only in terms of cooking time, but also in terms of energy used. Comparable time differences were also consistently noted at 100, 125, 150, 175 and 200 degrees F. Also surprising was the upper limit of temperature measured in the pans: the copper registered a max of 210F on my dairy thermometer and attained a roiling boil, whereas the others maxed out at lower temperatures (Al 202, Cast 207, and SS 206) and had less vigorous boils (the aluminum pan's was particularly feeble). While this embarrassingly proves the weakness of my hob, it also proves the relative efficiencies of the materials.
Following each boil test, I also timed cooling. The boiling pan was moved to a cool trivet and the time to cool in 25 degree steps was measured. The times to cool from boil to 125F were:
SS Clad 38:46
Cast Iron 40:51
The surprises here were that the water in aluminum cooled substantially faster than that in the copper pan, and the SS pan cooled it faster than did the cast pan. However, I did not have access to 3mm-thick aluminum or clad pans, so I think the much-thicker copper and cast pans tended to retain more heat than the thinner materials, and perhaps skewed the numbers.
Finally, I tested the pans to assess what hob settings would maintain a gentle simmer, both lidded and uncovered. The results were:
Copper 3 (2 lidded)
Cast Iron 4 (3 lidded)
Aluminum 4.5 (3.5 lidded)
SS Clad 5 (4 lidded)
If someone DOES have access to 4 same-sized pans of SAME bottom/wall thickness, and wants to run a similar test, I'd be interested in the results.