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Dec 19, 2010 09:46 PM

Even heat challenge -- copper diffuser plate?

I've been reading many of the recent threads about experiments comparing cookware of various materials with great interest. (As some may remember, I posted my own initial results a couple months back with an IR thermometer:


With all of these tests by so many people, we have empirical evidence that slow response materials like cast iron and stainless steel have hot spots that can produce significantly uneven heating and scorching under many common cooking conditions. But obviously people who love certain kinds of materials (particularly cast iron), still like them and want to use them for all sorts of reasons. I too would like to have a way to use my cast iron pans more often.

Here's what I'm wondering: what about those copper stovetop diffuser plates? Most I could find are 1/8" thick copper plates -- at least as thick as the 2.5-3.0 mm copper we see recommended for good copper cookware. Thus, they should be able to distribute heat across the surface of the plate as well as copper cookware.

Here are a couple links:

Obviously, one could get a piece of copper plate cut to spec from a sheet metal source as well.

Does anyone have experience using a copper plate to mediate between an uneven burner and an uneven pan? How does it work for you?

Just in theory -- assuming we have a pan with a flat bottom that mostly makes contact with the copper surface of a diffuser plate, could we transform a cast iron (or stainless) pan into a relatively even heating surface? Obviously, we'll lose some responsiveness, since the heat has to diffuse through a lot of metal -- but cast iron isn't good at responsiveness anyway, so would this be any worse? And we'll lose some efficiency -- extra heat is needed to raise the temperature of the copper, and it will radiate off exposed surface around the pan. But stovetop cooking energy use is usually pretty insignificant within household energy use (and it's already pretty bad in terms of heat energy efficiency).

We would effectively choose to even out the heat source before it reaches the pan, rather than even out the response of the pan. I know a number of people have suggested ways of making a more even heat source -- is this a reasonable one?

Even for fairly large copper plates, they cost less than $100 each. Even the smallest cheapest decent quality copper pan costs more than that. So, could a couple of these diffuser plates be a reasonable affordable alternative for someone who wants even heat but prefers to use cast iron or some other material for whatever reason? Obviously, this wouldn't be effective for pans without flat bottoms or for the occasional application that requires the sides of a pan to be as evenly heated as the bottom (where aluminum or copper pans are the only reasonable choices).

If these diffusers don't work well, why not? And if they do, why don't they come up as a good solution to some of the issues voiced in recent threads?

(Edit -- also, if these work, for those on a budget, an aluminum plate should be much cheaper, lighter, and also quite responsive. I don't see aluminum coming up in quick internet searches for home cooking, though I see some mentions for commercial applications, but one could easily get one custom cut from a metal shop. And since it wouldn't come in contact with food, it shouldn't be a concern for those who avoid aluminum cookware.)

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  1. They probably work. There appear to be a few solid aluminum heat diffuser/flame tamer on Amazon and other places:

    1 Reply
    1. re: Chemicalkinetics

      Thanks for the link. I did try searching Amazon quickly before, but I think I was using a different search term -- the stuff that showed up was either thin flimsy things or stuff like cast iron flame tamers, rather than aluminum. Some of these have promise, though I'm a little shocked at the price. Many of these are almost as expensive as copper plates in my links, but given how cheap aluminum is compared to copper, many of these seem to be quite pricey.

      I also saw when I did a quick Chowhound search before posting that you had recommended these to someone at least once before. Do you have personal experience? I've mostly heard of "flame tamers" as things to use when cooking stew or stock or something at a low simmer, and your burner wouldn't go low enough -- I don't know anyone who has actually used them for more general cooking applications.

    2. Athanasius: Yes, I think these hold real promise for evening out heat. My predictions include:

      GAS: A huge improvement for any pan that hotspots. And, if the disc is sized to the pan, one would retain the effects of hot combustion gasses flowing up the pan's sides. An oversized disc will tend to broaden the hob, making burners "larger".

      ELECTRIC: Not much actual improvement for resistive or radiant hobs, as these elements already deliver pretty uniform, high surface-area contact with pan bottoms. However, like with gas, electric hobs could be effectively enlarged.

      INDUCTION: Obviously a straight-gauge Al or Cu disk isn't going to do anything. But a bimetal disc with a bottom layer of ferrous alloy would work. If the underling induction coil is single-ring, and the appliance hot-spots with CI before, it would be a major improvement afterward. But if the coil adequately covers the pan bottom, the disc's effect would be more like on electric. A bimetal disc would be $$$, and I'm not sure how the detection circuits would like it if it was not optimally-sized.

      I have a large (maybe 20x12) 1/2-inch-thick AL trivet I'd be happy to test on, but I think to do this right, we'd be better off with you and your IR gun.

      I have to smile when I think about the 20th & 21st C. "advances" in cookware and appliances. We wouldn't be having this discussion (or the many others like it here), if everyone had smooth, flat, stable- and uniformly-heated surfaces on which to perch their thin, their uneven, their spotty pots. Kinda like a wood cookstove, an AGA or a commercial griddle. We probably wouldn't have tortured and bankrupted ourselves with sandwichware and magnets.

      12 Replies
      1. re: kaleokahu

        Thanks, kaleokahu. (And by the way, thanks for your experiments in this matter.) I agree with you that these things would be worthless for induction unless they were engineered, but on other stoves they could have some use.

        I also like this:

        "We wouldn't be having this discussion (or the many others like it here), if everyone had smooth, flat, stable- and uniformly-heated surfaces on which to perch their thin, their uneven, their spotty pots. Kinda like a wood cookstove, an AGA or a commercial griddle."

        Yeah, my current theory is that the apparently very old reputation of "even heat" for cast iron cookware comes from the past where old cookstoves or even open fires were the standard cooking apparatus. The same thing that makes a cast iron pan surface uneven on a modern range also makes it slow to change temperature. And when you have wood burning away in your stove or even directly under your pot, the heat source will flare up and down quite a bit. In that case, a material that can mediate and won't change temperature quickly is an asset -- whether it's the cast iron of an old wood stove or a thick cast iron pot/pan in a fire. The responsiveness of copper and similar materials would tend to make its temperature fluctuate a lot more with flare-ups, particularly over an open wood fire, and thus wouldn't be so "even heating."

        The advantage of the modern range, of course, is that it's a lot more efficient. The old cast iron woodstove had an even heating surface primarily because the fire spread out heat throughout the stove in all directions, "wasting" a lot of heat to cook one pot for dinner. (Of course, in reality, these stoves often contributed to heating your house, so the heat wasn't always wasted.)

        But, as you point out, efficiency comes at a price. So now we need something to distribute our small burner flames/coils to match our large pans. What I wonder is why it has taken so long for anyone to notice we might benefit from such things to cook on modern stoves with cast iron, etc.? Gas stoves have been common for a century.

        1. re: athanasius

          Wow, my head almost exploded reading this short thread......

          I use a round Griddle for one burner or a Griddle plate for two burners. Cheap and easy.

          1. re: fourunder

            fourunder: You can be forgiven for not staying completely awake here, LOL. The central topic was how to avoid/minimize hotspotting in poorly-conductive CI cookware by use of an aluminum or copper diffuser. How would putting another layer of CI down help very much?

            1. re: kaleokahu

              It mimics a solid top range like in a commercial kitchen, so you can control the heat better, e.g., by pulling off a fry pan from directly over the fire/burner, and transferring to the CI plate......but I use it when I make a small pot of Sunday Gravy in a consumer grade aluminum pot or stainless steel pot(thinner gauge). The CI doesn't create a burn spot like direct flame know, the spot where the tomato pulp or meat/chop meat collects.... and if you forget about stirring, it burns black. The CI griddle affords you some margin for error and forgetfulness, while using a higher flame, effectively increasing & dispersing the surface heat while minimizing the burn spot. Also, the double griddle plate allows you to mimic three burners, instead of two.....very handy when cooking for holiday parties.

                1. re: kaleokahu

                  The other way to look at this is that a cast iron flame tamer/heat diffuser effectively thickens the cast iron cookware. Any cookware (copper, aluminum, cast iron...) becomes more even heating when it becomes thicker, but it comes at a price of slower heat response.
                  A cast iron heat diffuser for a cast iron cookware actual makes some sense. Though a copper or aluminum heat diffuser will be better. On the other hand, a cast iron heat diffuser for a copper or aluminum cookware would be weird, I think.

                  1. re: Chemicalkinetics

                    Chem: Right on about the thickening.

                    "Any cookware (copper, aluminum, cast iron...) becomes more even heating when it becomes thicker."

                    But only within certain limits with low-conductivity metals. fourunder above was using it to prevent a scorchspot in a tomato sauce, essentially MODERATING the heat, not really spreading it out. There's that famous piece "Understanding Cookware..." that you've linked to in the past that has a great graphic of what happens when you thicken poor conductors--the heat "dome" created above the heat source just shrinks proportionally. There is less heat making its way through, sure, but the top part of the dome is actually SMALLER. Ergo, I think if you cooked on high heat with double-thick cast iron, you'd just have a smaller hotspot.

                    I understood athanasius to be more focused on evening than moderating.

                    1. re: kaleokahu

                      Yes, Kaleo -- I was basically asking the question: "If cast iron (or stainless or whatever cooking material) doesn't heat as evenly as copper/aluminum/etc., is there a way we can get it closer?"

                      As Chem and Fourunder note, you can minimize the problem of hotspots, which clearly is the source of the name "flame tamer," by putting a layer of whatever thick metal below your pan. My question is related -- how to not only make the heat source less damaging, but also spread it out more to make a less conductive pan behave more like more conductive pans.

          2. re: athanasius

            athansius: "What I wonder is why it has taken so long for anyone to notice we might benefit from such things to cook on modern stoves with cast iron, etc.?'

            Do you want the short(er!) answer, or the "end of Western civilization" answer? LOL, I'll spare everyone the latter. IMO, the advent of gas cooking (and later, electric) was never a huge advance in anything other than CONVENIENCE.

            What happened was, we all got used to (in reality, became dependent on) the convenience of gas and electric--and more lately MWs and induction. We erred on the side of convenience, and the problem of unevenness seemed like a small price to pay for not having to cut, split, stack, pack, and feed wood and dump ashes.

            The number of people who really cooked with woodstoves or over open hearths got smaller and smaller, and so we lost sight of the bargains we'd struck for convenience. My maternal grandmother, who died in 1968, cooked her whole life on and in a woodstove that was already old when it was installed in her parents' new house in 1897 (She persisted with it even after the cheap firewood supply was gone, using flakes of Prestologs).

            Interestingly, with the shift to gas, many companies offered early conversions where the retrofitted gas jets were positioned under the same part of the thick CI woodstove cooktop as where the firebox had been. I've never cooked on one, but I believe they worked well. In fact there are still a few restorers of vintage woodstoves that will--for a price--convert these to gas (and electric). Now they're considered cool relics, but in the 20's and 30's they were looked down upon. Sort of like how people willingly junked grand touring cars like the Cords and La Salles to buy Packards and Fords.

            I'm fascinated by the gyrations and gymnastics attendant to trying to approximate that old, evenly-heated cooking surface. If you think about it, the sandwichware I often slander and besmirch has fitted to/in it a little bit of "woodstove"--or trivet/diffuser, if you like.

            I say you're onto something--let's try putting the "woodstove" back where it belongs--on the cooktop. If they work as well as I suspect they will, most folks should have one.

            PS Tom Keller calls for use of diffusers in making things like garlic confit--and not just on extreme low heat settings, either.

          3. re: kaleokahu

            Did you ever test the trivet? Or did you post it and I missed it?

            1. re: rbraham

              Nope, it's still at my other house.

              1. re: kaleokahu

                What a great reply! I wish I could use it, and I would at every conceivable opportunity.

          4. Athanasius,

            I'm late to this discussion but here's my input: Like you, I wanted a copper diffuser but those offered at retail such as in cooking magazines are expensive and somewhat thin; you can find various thicknesses at commercial metal distributors, even pre-cut into discs, but I hoped to find something less expensive. A local metals scrap yard that used to be a great place for that kind of thing said they rarely have any copper plate these days but they did have a sheet of 1/4" aluminum that was a bit rough (had some dried cement on it, scratches, etc.) but wasn't much money so I got it. I briefly considered using it as is as a solid top on my stove since it neatly covered all four of my stove's burners, but I decided that heating up the entire sheet for just one pan wasn't very efficient, so I had a friend with a metal band saw cut me four discs of varying diameters, up to my largest pan's size.

            Well, I'm totally sold on them and now use them just about all the time, always if I'm using a copper or enameled cast iron pan. I truly think they even out the heat and give me much more control over the cooking.

            Copper is, of course, a better conductor, but aluminum is pretty good and for what I paid I'm very happy.

            Here's a metals distributor if you've got to have copper (there are lots of others - just Google "copper sheet":


            1. I have just run across an ad for Bella Copper and am having the same questions about popping for this expensive but promising resource.

              I see this thread is nearly a year old, so, did any of you ever try a copper diffuser? What were your results?

              Thanks in advance.

              1. Could someone sum up what we are talking about?

                1) Diffusers/"hot plates" for more control of heat--particularly useful when low steady heat is required and the gas hob can't stay low enough--as well, by the same principle, spreading around/evening the heat around a single piece of equipment; OR

                2) A copper or aluminum plate that does the same thing, and by its width or use of arcane (to me) principles of convection or conduction, can allow me to use an 11-in. Pan on a standard burner, thus leaving a sizeable ring of pan-bottom hanging over thin air; and

                2a) A plate that I can over multiple burners, eg bellacopper?

                I am most interested in 2) and 2a), insofar as they can be distinguished from 1).


                6 Replies
                1. re: rbraham

                  Hi, Rob:

                  1) Diffusers or "flame tamers" are largely designed to moderate the heat that reaches the pan. They may, but need not be made of conductive material. They function as stove trivets. On modern adjustable hob stoves, the only reason to moderate heat is if the hob won't adjust low enough.

                  2) In addition to serving this moderation function, a plate can, at all heat settings, effectively widen the hob and make it more even. This can help when the cookware and/or the hob are mismatched or prone to hot-spotting (e.g., big CI skillet on small, cheap gas hob). Obviously, plates of Cu and Al are better at moving heat out toward the edges of the plate than are iron and steel.

                  2a) If you plan to straddle two active hobs with one plate, the evenness of the heat will be better with Cu or Al. It still won't be perfect, but will be better than if you used a CI griddle. An advantage of doing this is that you can fit more or differently-sized pans onto the one expanded surface (e.g., a fish poacher or oval skillet).

                  You might enjoy: and

                  For awhile now I've been on the lookout for a chunk of 1/4" copper plate. But since I recently switched to a wood cookstove, I don't have the need any more.


                  1. re: kaleokahu


                    You chose 1/4-in as a min? I'm looking into going to some metal shops. Check this out:


                    And, at the same cite,


                    Where they mention that gauge as being good for "heat diffusers." (Other rectangular cut are also available, of course.) On eBay now,


                    Is a sheet for a tiny price. I'm trying to get my brain together to sort out the thicknesses and the terminology; mm doesn't equal millimeters for starters.

                    It would help for me simply to call BellaCopper for their thickness for starters, but i haven't taken my meds yet and I'm whacked.


                    1. re: rbraham

                      Hi, Rob:

                      No, not a minimum. But if I find a chunk of "scrap" that thick (0.250), I'm going to have it made into a Genoise pan.

                      0.125 (a/k/a 1/8", 3.175mm, or 8-gauge) is quite good. $75 for a round 9" diffuser you can use under all your cookware is a pretty good investment.


                      1. re: kaleokahu

                        BellaCopper, and a number of posters, have mentioned that if you match up two large rectangular plates, you can use the between-the-hobs space as a keep warmer.

                        I can only see keeping a small cup of butter liquid, not any normal amount of food in a pot. This has bearing on those circular (cheaper) plates vs. those of BellaCopper.

                        Any experience, math (for me, for pleasure), or dig out the IR gun?

                        1. re: rbraham

                          Hi, Rob: " can use the between-the-hobs space as a keep warmer."

                          It's a little better than that--depending on your settings, you can *cook* between the hobs. Many folks do, as witnessed by the popularity of griddles that straddle hobs. The heat won't be perfectly even, is all.


                      2. re: rbraham

                        BellaCopper is featured on Daily Grommet today--I posted a question about the thickness, they are 1/8" thick and the 10" one weighs 4 lbs!