Induction Cooking: How It Works

Here's the Basic Idea

"Cooking" is the application of heat to food. Indoor cooking is almost entirely done either in an oven or on a cooktop of some sort, though occasionally a grill or griddle is used.

Cooktops--which may be part of a range/oven combination or independent built-in units (and which are known outside the U.S.A. as "hobs")--are commonly considered to be broadly divided into gas and electric types, but that is an unfortunate oversimplification.

In reality, there are several very different methods of "electric" heating, which have little in common save that their energy input is electricity. Such methods include, among others, coil elements (the most common and familiar kind of "electric" cooker), halogen heaters, and induction. Further complicating the issue is the sad habit of referring to several very different kinds of electric cookers collectively as "smoothtops," even though there can be wildly different heat sources under those smooth, glassy tops.

As we said, cooking is the application of heat to food. Food being prepared in the home is very rarely if ever cooked on a rangetop except in or on a cooking vessel of some sort--pot, pan, whatever. Thus, the job of the cooker is not to heat the food but to heat the cooking vessel--which in turn heats and cooks the food. That not only allows the convenient holding of the food--which may be a liquid--it also allows, when we want it, a more gradual or more uniform application of heat to the food by proper design of the cooking vessel.

Cooking has therefore always consisted in generating substantial heat in a way and place that makes it easy to transfer most of that heat to a conveniently placed cooking vessel. Starting from the open fire, mankind has evolved many ways to generate such heat. The two basic methods in modern times have been the chemical and the electrical: one either burns some combustible substance--such as wood, coal, or gas--or one runs an electrical current through a resistance element (that, for instance, is how toasters work), whether in a "coil" or, more recently, inside a halogen-filled bulb.

Induction is a third method, completely different from all other cooking technologies-- it does not involve generating heat which is then transferred to the cooking vessel, it makes the cooking vessel itself the original generator of the cooking heat.

(Microwaving, an oven-only technology, is a fourth method, wherein the heat is generated directly in the food itself.)

How does an induction cooker do that?

Put simply, an induction-cooker element (what on a gas stove would be called a "burner") is a powerful, high-frequency electromagnet, with the electromagnetism generated by sophisticated electronics in the "element" under the unit's ceramic surface. When a good-sized piece of magnetic material--such as, for example, a cast-iron skillet--is placed in the magnetic field that the element is generating, the field transfers ("induces") energy into that metal. That transferred energy causes the metal--the cooking vessel--to become hot. By controlling the strength of the electromagnetic field, we can control the amount of heat being generated in the cooking vessel--and we can change that amount instantaneously.

(To be technical, the field generates a loop current--a flow of electricity--within the metal of which the pot or pan is made, and that current flow through the resistance of the metal generates heat, just as current flowing through the resistance element of a conventional electric range's coil generates heat; the difference is that here, the heat is generated directly in the pot or pan itself, not in any part of the cooker.)

How Induction Cooking Works:

1. The element's electronics power a coil (the red lines) that produces a high-frequency electromagnetic field (represented by the orange lines).

2. That field penetrates the metal of the ferrous (magnetic-material) cooking vessel and sets up a circulating electric current, which generates heat. (But see the note below.)

3. The heat generated in the cooking vessel is transferred to the vessel's contents.

4. Nothing outside the vessel is affected by the field--as soon as the vessel is removed from the element, or the element turned off, heat generation stops.

(Image courtesy of Induction Cooking World)

(Note: the process described at #2 above is called an "eddy current"; heat is also generated by another process called "hysteresis", which is the resistance of the ferrous material to rapid changes in magnetization. The relative contributions of the two effects is highly technical, with some sources emphasizing one and some the other--but the general idea is unaffected: the heat is generated in the cookware.)

(You can see what such a coil and its associated electronics looks like in the image at the right.)

There is thus one point about induction: with current technology, induction cookers require that all your countertop cooking vessels be of a "ferrous" metal (one, such as iron, that will readily sustain a magnetic field). Materials like aluminum, copper, and pyrex are not usable on an induction cooker. But all that means is that you need iron or steel pots and pans. And that is no drawback in absolute terms, for it includes the best kinds of cookware in the world--every top line is full of cookware of all sizes and shapes suitable for use on induction cookers (and virtually all of the lines will boast of it, because induction is so popular with discerning cooks). Nor do you have to go to top-of-the-line names like All-Clad or Le Creuset, for many very reasonably priced cookware lines are also perfectly suited for induction cooking. But if you are considering induction and have a lot invested, literally or emotionally, in non-ferrous cookware, you do need to know the facts. (Check out our page on Induction Cookware.)

(And there are now available so-called "inductions disks" that will allow non-ferrous cookware to be used on an induction element; using such a disk loses many of the advantages of induction--from high efficiency to no waste heat--but those who want or need, say, a glass/pyrex or ceramic pot for some special use, it is possible to use it on an induction cooktop with such a disk.)

On the horizon is newer technology that will apparently work with any metal cooking vessel, including copper and aluminum, but that technology--though already being used in a few units of Japanese manufacture--is probably quite a few years away from maturity and from inclusion in most induction cookers. If you are interested in a new cooktop, it is, in our judgement, not worth waiting for that technology.

(The trick seems to be using a significantly high-frequency field, which is able to induce a current in any metal; ceramic and glass, however, would still be out of the running for cookware even when this new technology arrives--if it ever does.)

There is also now the first of the new generation of "zoneless" induction cooktops. These essentially make the entire surface of the unit into a cooking area: sensors under the glass detect not only the presence of a pot or pan or whatever, but its size and placement--and then energize only those mini-elements directly under the cooking vessel. You can thus put any size or shape of vessel--from a small, traditional round pot to a gigantic griddle or grill--down anywhere, in any alignment, and the unit will heat it, and only it (or, of course, seveal "its", as may be).

Quoting AEG's brochure: "The hob senses the size of the pan and only heats the exact area covered by the pan. The Maxi-sense range [uses] ‘flexible sections’ to create an all-over cooking surface. Pans can be placed anywhere on the hob as long as the section marker is covered, eliminating the restriction of traditional specific zones [ = elements]. It does not matter how many pans you have or what size they are, whether it is a fish kettle, a small milk pan, or tagine . . . ."

This technology has only been around since about 2006, and in fairness it must be said that early reports on the prototypes were not all that one might have hoped for; De Dietrich, which is to say the Fagor Group, led then, but the prototype as distributed for testing had problems remembering where things were if they were moved about any, and also with uniform heating. Presumably, the engineers learned from what they heard, because such units are now in production and available (sort of--see the note below). We see, though, that Electrolux is into this technology in a substantial way in some of their induction lines, such as AEG. De Dietrich calls it "Continuum", AEG calls it "Maxi-sense" (as seen at the left). One supposes that soon everyone will have it; we feel it is clearly the future of induction, which in a way is to say the future of cooking, for it won't be so long now before gas for cooking is looked back at in the same way we today look back on coal and wood.

The only lines we know of with this technology are Fagor's De Dietrich--its premium, "upmarket" line--and Electrolux's AEG, neither of which is regularly distributed in North America; there is, however, one distributor in Canada--who apparently also ships to the U.S.--who handles some parts of the AEG line, parts which just recently expanded from two induction units to three, the new one being one of AEG's "zoneless" types, though one of only 6.9 kW total and three zones (yes, Virginia, even "zoneless" units have zones) and a somewhat strange profile, wide but shallow. We have no pricing or availability data.

There is also now such a thing as an induction oven. (It looks as if the usual heating coil on the base of the oven has been replaced by a ferrous plate, which is energized to heat by embedded induction coils beneath it--so any sort of bakeware will work in it.) Expect to see more such things before long.

Now Let's Take a Closer Look

(In this part, we use a little math--but don't shudder, it's all just arithmetic!)

First, let's define some terms. Energy is a quantity: it's like a gallon of water. In cooking, we aren't really concerned with actual energy--we want to know at what rate a cooking appliance can supply energy. It's like, say, a garden hose: if it can only produce a dribble of water, it doesn't matter to us that if we let it run day and night we could eventually fill many buckets. What we want to know is how forcefully that hose can spray--how many gallons a minute it can put out--because that's what does useful things for us in some reasonable amount of time.

So, in discussing cooking appliances, we normally talk about energy flow rates, which are just like the water flow rates expressed in "gallons a minute"--that is, we want to be able to know at what rate we can pump heat into the cooking process. For gas, energy content (quantity) is traditionally measured in "British Thermal Units" (BTU), and so the flow rate of gas energy is given in BTU/hour. For electricity, energy content is normally measured as "kilowatt-hours" (kWh) and the flow rate is just kilowatts (kW).

(Let's restate that, because it often confuses people, being sort of "upside down". A kilowatt is not a quantity, it's a rate, like "knots" to measure speed at sea--there are no "knots an hour", knots are the speed, and kilowatts are the electrical energy-flow rate. To measure total energy--as, for instance, your electric-supply company does, to know how much to bill you--we multiply the flow rate, kilowatts, by the time the flow ran, hours, to get "kilowatt-hours" of energy. So BTU/hour and kilowatts are both measures of energy flow rates, not of energy itself.)

The energy in gas and the energy in electricity just happen to be measured in different-sized numbers, but they're measuring the same thing. It's like miles vs. kilometers: we can say a place is about 5 kilometers away, or that it's a little over 3 miles away, but the actual distance we'd have to walk or drive is the same. We can easily convert from miles to kilometers if we know how many of one make up the other. Likewise, we can easily convert from BTU/hour to kilowatts (or vice-versa). There are just about 3,400 BTU to a kWh--or, more exactly, about 3,413. (Keep in mind that a kilowatt is 1,000 watts: 1 kW = 1000 W).

Superficially, then, comparing cooking technologies looks easy: can't we just look at the rated kW or BTU/hour of a cooktop, and simply convert one kind of measure to the other to compare them? Nope. The complication is that the various technologies are not all equally effective at converting their energy content into cooking heat; for example, gas delivers little more than a third of its total energy to the actual cooking process, while induction delivers about 85 to 90 percent of its energy.

That means that if we have a gas cooker capable of putting out X BTU/hour, converting that X to kilowatts does not tell the story--because a lot more of that X is wasted energy that doesn't do any cooking than is the case with induction. To truly compare the cooking power of a gas cooker and an induction cooker, we indeed need to first convert one measure to the other, say BTU/hour to kilowatts; but we then need to slice off from each unit's nominal output the amount that does not get used for cooking.

(Think again of garden hoses: if we have two hoses and each is getting, say, 5 gallons a minute pumped into it by the water tap it's screwed onto, are they the same? Not if one has a pinhole leak while the other has a gaping rip. The amount of water that comes out the nozzle to do whatever we need done will differ drastically from one to the other. Induction cooking has a pinhole leak, maybe 10% to 15% of the raw energy it takes being wasted; gas cooking has the whacking great rip in it, the average unit wasting over 60% of the raw energy it consumes.)

So, to see how induction compares to its only real rival, gas, we have to make the following calculation:

BTU/hour = kW x 3413 x E_ind/E_gas

That last term there--E_ind/E_gas--is simply the ratio of the two methods' real efficiencies: E_ind is the energy efficiency of a typical induction cooker and E_gas is the energy efficiency of a typical quality gas cooker.

The snag comes when we try to find reliable figures for those efficiencies. It is remarkable how much misinformation there is (especially on the internet), largely from well-meaning but ignorant sources who do not understand the issues, or are simply repeating what they read elsewhere (from someone else who does not understand the issues). For example, the energy-efficiency values quoted by various induction-cooker makers range from a low of 83% to a high of 90%, while values given for gas cooking run, depending on the source, from 55% down to as little as 30%, nearly a 2:1 ratio.

Fortunately, in the last few years some standardized data from disinterested sources have become available, so we no longer have to rely on figures from parties with an axe to grind. The U.S. Department of Energy has established that the typical efficiency of induction cooktops is 84%, while that of gas cooktops is 40% (more exactly, 39.9%)--figures right in line with the range of claims made for each, and thus quite believable.

Using those values (and sparing you the in-between steps), we can say that gas-cooker BTU/hour figures equivalent to induction-cooker wattages can be reckoned as:

BTU/hour = kW x 7185

It is worth noting that the testing method that established the induction data used, in essence, a slab of ferrous metal as the "vessel". It reliably established what might be called a "baseline" efficiency, and that is why we use it throughout in evaluating energy equivalencies. It remains as a possibility that particular items of induction equipment--and, for that matter, of cookware--may be a bit more or less efficient than the baseline. There are at least plausible reports that some makes, coupled with some items of cookware, can achieve true efficiences close to 90%. On this site, we do not use that value because we do not yet know of any definite, reliable data, but you should keep it clear in your mind that when we discuss the gas heating-power equivalencies of induction units, we are using what should be considered rather conservative numbers; chances are that many induction units are actually somewhat more powerful (in BTU/hour equivalents) than we set forth.

In fact, Panasonic states for several of its units that efficiency is 90%, noting that: Heating-efficiency measurements were taken based on standards of the Japanese Electrical Manufacturers' Association and using a Panasonic standard enamelled iron pot. Also: a University of Hong Kong research product showed induction efficiencies from 83.3% to 87.9%, numbers clearly in line with 84% as a minimum and 90% as possible.

So How Much Power Is What?

Perhaps the most useful way to use that conversion datum is to see what good gas-cooker BTU values are and work back to what induction-cooker kW values would have to be to correspond. But what are good gas-cooker BTU values? Here too, opinions will vary. As a sort of baseline, we can look at what typical mid-line gas ranges look like. As numerous sources report, a typical "ordinary" home gas range will usually have its burners in these power ranges, give or take only a little: a small burner of about 5,000 Btu/hour; two medium-level burners of about 9,000 Btu/hour; and (depending on width, 30 inches or 36 inches) either one or two large burners of anywhere from 12,000 to 16,000 BTU/hour

When one moves from stock home appliances up to the deluxe level (sometimes called "pro", though ironically the warranties for such units expressly forbid commercial use), gas ranges and cooktops naturally become more powerful. On these, burner powers run up to 18,000 BTU/hour or thereabouts (one highly regarded specimen of this class has four 15,000-BTU/hour burners and two 18,000-BTU/hour burners). One expert source remarked of such gear: Most commercial-style home ranges offer 15,000 BTUs per burner, which is perfectly adequate for most at-home cooks. You won't always need all that heat, but if you want to caramelize a bell pepper in seconds, or blacken a redfish like a pro, well, you'll need all the heat you can get. My advice: Go for the big-time BTUs (which, in the tests he was discussing, was that 18,000 BTU/hour level).

So let's summarize by showing representative gas-power levels and their induction-power equivalents (remember, calculated quite conservatively):

• Typical home stove:
  
  • small: 5,000 BTU/hour gas = 0.70 kW induction
  • medium: 9,000 BTU/hour gas = 1.25 kW induction
  • large: 12,000 BTU/hour gas = 1.70 kW induction; or 15,000 BTU/hour gas = 2.10 kW induction
    
    
• Typical "pro style" stove:
  
  • medium: 15,000 BTU/hour gas = 2.10 kW induction
  • large: 18,000 BTU/hour gas = 2.50 kW induction

(Even for wok cooking, the most power-hungry kind there is, experts consider 10,000 BTU/hour good and 12,000 BTU/hour "hot".)

So how do actual real-world, on-the-market induction cooktops stack up against gas?

It's an almost comic mismatch. Sticking to build-in units (as opposed to little free-standing countertop convenience units), it is difficult, perhaps by now impossible, to find a unit with any element having less than 1.2 kW power--which puts the smallest induction element to be found equal to the average "medium" burner on a gas stove. The least-expensive 30-inch (four-element) induction cooktop has:

• a 1.3-kW small element (between 9,000 and 9,500 BTU/hour),
• two elements of 1.85 kW each (well over 13,000 BTU/hour), and
• one element of 2.4 kW (over 17,000 BTU/hour).

The least-expensive 36-inch (five-element) induction cooktop has:

• a 1.2-kW small element (8,500 BTU/hour),
• a medium element of 1.8 kW (13,000 BTU/hour),
• a larger element of 2.2 kW (16,000 BTU/hour),
• and two elements of 2.4 kW (over 17,000 BTU/hour).

The very highest-power gas burner to be found in the residential market is 22,000 BTU/hour, and that's a sort of freak monster, whereas a 3.6-kW and 3.7-kW element--which is around 26,000 BTU/hour of gas!--is found in many induction cooktops. (Moreover, the elements on some induction units can share power with one another, so that if not every element is already in use, a given one can be "boosted" beyond its normal power level, for uses such as bringing a large pot of water to a boil, or pre-heating a fry skillet.)

So, in sum, induction is not "as powerful as gas"--it's miles ahead.

(There is, incidentally, a lesson there: even really serious cooking does not, save for perhaps a few specialty cases, require stupendous amounts of power, and you should not be seduced into choosing between units sheerly on the basis of the maximum available firepower per element. For one thing, most units of the same size have total maximum unit capabilities that are nearly identical: the differences lie in how they distribute that total among the unit's elements, which are invariably four on a 30-inch-wide unit and five on a 36- inch-wide unit. When a pro tells you that really "big-time" power is the equivalent of around 2.5 kW of induction, you should ask yourself whether getting elements with significantly more power than that really should be a major consideration in your decision-making process.)

Induction Cooking: Pros and Cons 2

Inadequate Power?

This is not a valid negative--but we list and discuss it here because there are so many falsehoods and misunderstandings floating around on this matter. As we clearly showed, with hard numbers, induction cooking units are not merely as powerful as even "pro" gas ranges (residential "pro", that is), they are almost invariably much more powerful. (And that's using conservative figures for both gas and induction efficiencies.) To recap, a top-line (and top-price) so-called "pro" home gas range might have burners each rated at 15,000 BTU/hour or, in a few cases, as much as 18,000 BTU/hour--but that is only about 2.1 to 2.5 kW for induction elements, and even the most modest cooktops have at least one element of at least 2.4 kW (and many have elements up to 3.6 or 3.7 kW!). Any concern over the adequacy of the "cooking power" of induction units is simply silly.

Radiation Hazards?

Owing to the length of quoted material involved in our discussion, we have put this topic on a page of its own; but the real scientific literature seems to show rather clearly that there are simply no radiation-associated hazards, even for those with imbedded cardiac devices. The fields are very localized, and in any event the cooking vessel absorbs virtually all of the field energy (and if there is no cooking vessel on an element, it won't turn on). You should certainly read about it for yourself, but claims of hazard seem quite groundless.

Noise

Induction itself is a noiseless process: the energy fields are generated by electronic equipment, which is silent. But even efficient electronics generates some heat. Whether the amount of heat generated can be dissipated "passively" (just by radiation and natural air flow, still silent) or requires a small fan to augment the air flow depends in good part on how tightly a given maker has packed how much power into how much space--some units have fans, some don't. But even on those with fans, one, the fan does not necessarily run all the time--usually just when the unit is running multiple elements at high settings--and two, such fans are normally pretty soft-sounding. There can also an occasional very soft "tick" sound, as the power controller cycles the elements on or off to keep the element power steady and stable.

What can sometimes produce sound with induction cooking is not the induction equipment but the cookware itself. Some of the possible causes include:

• Encapsulated slugs in the base of the cookware: "clad" cookware (which is what any stainless-steel-finish cookware that works on induction is) has as its base a sort of "sandwich" of layers of several different metals (typically steel outside, aluminum or sometimes copper in the middle, and more steel inside); if the middle layer is merely encapsulated in the steel, as opposed to being actually welded within it, it can move about, however microscopically; but any such microscopic play can give rise to a sort of "buzzing" noise. On some other cooking surface, that buzzing won't happen, but the high-frequency oscillations of induction's magnetic field can cause it in lower-quality clad cookware (but even then, only on higher-power settings). When it occurs it's not typically loud, but it can annoy some people. Again: it's not the induction equipment, it's the less than ideal cookware, but it is an induction-related phenomenon.

• Loose-fitting handles on cookware, typically when riveted on, can vibrate slightly.

• Pans with irregular bottoms can vibrate audibly on the glass surface, though again typically only at high-power settings.

• At high-power settings, lighter-weight lids may occasionally vibrate a bit.

Cookware of solid cast iron, including enamelware, is not subject to such issues; and clad cookware of the top lines should not be.

Electricity Failures

If the electricity supply to your home is interrupted, you will be unable to cook; gas supplies can be interrupted, too, but such interruptions are normally somewhat less likely than electricity interruptions. If the electricity where you are frequently goes out for hours at a time, the loss of cooking ability may be an issue for you. Most people living in such circumstances will have provided themselves with a backup, such as a propane-powered emergency generator--but if that's you and you have no backup, factor the matter into your decisions.

No "Char" Flames

For those to whom charring such items as peppers in an open flame is important, the lack of such a flame is a drawback. (It is, of course, one shared with all non-gas cookers.) But nowadays, most good ovens--gas certainly, but probably even electric--can do an acceptable job of charring food.

Neutral Or Hard to Reckon

Energy Costs

Energy-cost differences are hard to reckon because the prices of gas and the price of electricity these days are highly volatile, even relative to one another (the DOE--the U.S. Department of Energy--reports that between 1999 and 2008, the national annual average residential natural gas price more than doubled), and vary considerably from locale to locale even on the same day at the same hour (and, of course, by season, too), sometimes by as much as a 3:1 ratio. But in any event, it is not a really large factor: according to the DOE (Table A.4), cooking accounts for only about 2.7 percent of an average home's energy use--and that use includes ovens, toasters, microwaves, and whatever else, not just stovetop cooking. The difference in cost for various cooktop energy sources is at most on the order of a couple of dollars a month.

Where does that come from? In November of 2009, on a national average, induction-cooking electricity cost about 1.43 times what gas-cooking cost (gas was $11.25 per thousand cubic feet, about 1,020,000 BTU, while electricity was 11.33 cents a kilowatt-hour, and 1 kilowatt-hour equals about 7,185 BTU). Overall household energy costs were estimated by one source--and this is a big variable--at $5 to $10 a day. Assuming, then $7.50 a day, that's about $228 a month, of which on average 2.7%, or roughly $6, goes for cooking costs. The 43% greater cost of electricity would be about $2.60, but that's way high because it assumes that all of the cooking energy is used for stovetop cooking, and that all households were using gas, the lowest efficiency method, for their cooking. So a couple of bucks a month is probably too high an estimate.)

As one often-quoted energy resource site put it, Most people can't save much energy by changing their cooking methods. That site estimates saving about $13 a year for gas cooking rather than electric, and that's not induction electric, which is significantly more efficient than most other electricity-powered cooking methods. So perhaps even a buck a month difference is too high an estimate. In short, the energy cost differences just don't matter. (Which, of course, is why they're in this "neutral" category.)

Purchase Costs

It's hard to say that induction units are "comparable" to, much less cheaper then, gas cookers when their prices start at well over a thousand dollars: nonetheless, we will say it. The reason we do is because one needs to be careful to compare apples to apples, and the conventional 30-inch slide-in kitchen stove is an orange in this analogy. It is not always true that "you get what you pay for", but it is always true that you don't get what you don't pay for. An induction unit is so clearly superior, in so many ways, to any other form of cooking that it is hard to exaggerate the differences. One can say that a Chevy and a Rolls Royce are both "cars"--vehicles that take a given number of passengers from Point A to Point B--but there are valid reasons for the difference in their prices.

Moreover, a cooker--ordinary, fancy gas, induction, whatever--is a very long-term investment. The cost difference between a simple, inexpensive plain kitchen stove and a decent or better induction unit is not much when averaged out over the likely lifetime of such a unit. Consider: right now (2/10), Consumer Search's preferred gas range with convection oven costs about $800; an induction-top range with convection oven (and the warming drawer the other lacks) can be had for $1,770. Yes, that's quite a difference; but amortize the $970 difference over the useful lifetime of such an appliance and it's maybe a buck a week.

But back to that "apples to apples": if one compares prices for induction units with those of comparable power and quality gas cookers, they are more than competitive. That $800 mentioned quickly doubles or trebles--and just for a cooktop, no oven--when one gets into the high-end gas equipment that is the only kind of gas cooking comparable in power to induction. For a top-line four-gas-burner-top range with 18,000 BTU/hour burners, one sees prices very close to $4,000, not the $800 mentioned above for an ordinary kitchen range. So if $1,770 is a lot more than $800, it's an even greater lot less than $3,900. Apples, oranges: take care.

Vessel Sizes

Cooking vessels at the extremes of size--the very small and the very large--occasionally raise issues. Because the auto-detect feature that all induction units have is meant to assure that things from cooking implements (such as metal tongs or spoons or ladles) to jewelry (rings or bracelets) will not activate an element, the detectors are often set rather conservatively, so much so that on some units very small pots or pans will not be detected (the usual minimum pot base size for activation is from 4 to 5 inches, depending on particular unit.) But that is scarcely a major issue: if you really must have such a pot--say "a butter warmer"--there are accessories available that make it easy.

At the other extreme--things like griddles or fish poachers that are well over 12 or 14 inches in at least one dimension--also present issues; but we list this as "neutral" because those issues are not substantively different from induction to, for example, gas. An induction element heats a cooking vessel placed on to the width of the element--just as with, for example, a gas burner. If one places a 12-inch-diameter skillet on a 9-inch induction element, the actual heat generation will take place in a 9-inch-diameter zone in the pan bottom; likewise, if one places the same skillet on a same-size gas burner, so also will the heating be limited to the size of the burner diameter. Heated cookware will do one of two things, depending on its construction (see out page on cookware for more detailed explanations): vessels designed to accomodate rapid changes in cooking temperature, such as clad stainless-steel cookware, will be correspondingly rapid in spreading heat throughout their total cooking area; vessels intended for even-temperature cooking, such as cast iron (enamelled or not), will be slower to achieve temperature equilibrium, but once well heated will hold temperatures pretty even and constant across their total cooking area.

On any cooking technique whatever, heat is only delivered or supplied within the diameter of the zone--gas burner, induction element, heater coil, whatever. Any vessel nontrivially larger than that zone will invariably be a little less hot at the outer edge of the cooking zone. That is a fact of life independent of the cooking technology, and is thus neither a plus nor a minus for induction compared to other methods.

(A very limited number of induction cooktops come with an induction-powered "bridge" between one element pair that allows the pair plus the intervening bridge to function as a single large area, conveniently griddle/grill-shaped.)

Actually, though, in the present state of the art induction is gaining the clear advantage as "zoneless cook-anywhere" induction cooktops--meaning that the entire surface is a cooking "zone"--become more and more prevalent. On such units, an "element" is defined by the size and shape of the cooking vessel placed on the surface: the entire cooktop is underlain by a very large number of small "micro-elements", and those micro-elements lying under a vessel ware what is activated by its presence. Grills, griddles, fish poachers, super-large skillets--all are heated uniformly merely by being placed anythwre on the cooktop. This is not guessing or "futurology": units that actually work that way are to be had right now from well-known makers (but, regrettably, for unknowable reasons, so far not yet in the North American market).

Get Others' Opinions

If you would like to take a current look at what is being said about induction cooking by actual users, not "authorities", here are some direct links. Each will do a realtime Google search for the word induction used in any discussion. The first is an especially good web resource; the other two are usenet ("groups") discussion forums. The difference between the last two is that one will search one set of groups--all those with the word cooking anywhere in their name--and the second another group, all those with the word food anywhere in their name (of course, there will be some overlap between those two sets of results, notably rec.food.cooking):

• the GardenWeb forums, where much and frequent discussion of induction equipment and cooking is to be found.

• "cooking" groups (such as rec.food.cooking, alt.cooking-chat, and alt.creative-cooking)

• "food" groups (such as rec.food.cooking and rec.food.equipment, an especially relevant group)

The GardenWeb posters tend to be everyday folk; the usenet posters tend to be more various. In any event, using these links gives you a set of results over which we have no control at all, so it's as unbiased as it gets (the selection is unbiased: many of the posters will be highly biased one way or another--see the text immediately below for examples of what we mean).

Cracked Pots

No, not the cookware you might use, but the crackpots who post nonsense about subjects about which it is manifest that they are sorely uninformed, thus creating false worries in the minds of those who expect authoritative-sounding posts to actually be authoritative. As some wit once remarked, "There is no harm in being a fool; harm lies in being a fool at the top of your lungs." And the internet, whether the web or usenet, is chock full of cracked pots apparently willing to be fools at the tops of their lungs about induction cooking and induction equipment.

We used to have here a little selection of cracked-pot postings, with our explanatory comments appended, but there's really little point to it now. Once, when so little was generally known about induction in North America, cracked pots could get away with posting ignorant (and usually snotty) nonsenses about the inferiority of induction and the supposed vast superiority of gas--but those days are gone now.

Not that there aren't likely to still be a lot of cracked pots out there--this is the human race we're talking about--but hard, factual data is now readily adduced. One could, for example, if given to being tediously supererogatory, compile a long laundry list of top-rank chefs and restaurants that use, and extravagantly endorse, induction equipment, as a sort of "Take that!" to those who insists that "the pros" use nothing but gas; but there would be no point except to prove a willingness to scan a lot of web pages, because so very many top chefs and restaurants would make that list.

The old guff seemed to be especially based on the purported weakness of induction units beside gas cookers; today, to anyone who can read without moving their lips, that scarcely rises even to the level of being humorous--it's just so silly. Remember:

BTU/hour = kW x 7185

Most household units have at least 2.4 kW elements, and many have 3.6 kW; that is very conservatively equivalent, for gas cooking, to 17,000 BTU up to just almost 26,000 BTU. That is cooking power, and it's commonplace in home units. Nuff said, hm?

Summing Up

Although this site is about the clear superiority of induction to any other method of cooking, we really have tried to give as balanced a picture as possible. If it seems to you, after reading this page, that we have skewed toward the favorable, that is only because induction really is immensely superior. Its sole consequential drawback is its inability to work with certain kinds of cookware--which is not an inherent flaw, because it works with the very best--but which can be a drawback is you are at present heavily invested (whether in a dollar or in an emotional sense) in incompatible cookware.

Induction Cooking: Pros and Cons

Favorable:

Instant Adjustment

To serious cooks, the most important favorable point about induction cookers--given that they are as or more "powerful" at heating as any other sort--is that you can adjust the cooking heat instantly and with great precision. Before induction, good cooks, including all professionals, overwhelmingly preferred gas to all other forms of electric cooking for one reason: the substantial "inertia" in ordinary electric cookers--when you adjust the heat setting, the element (coil, halogen heater, whatever) only slowly starts to increase or decrease its temperature. With gas, when you adjust the element setting, the energy flow adjusts instantly.

But with induction cooking the heat level is every bit as instantaneous--and as exact--as with gas, yet with none of the many drawbacks of gas (which we will detail later). Induction elements can be adjusted to increments as fine as the cooker maker cares to supply, just like gas, and--again very important to serious cooks--such elements can run at as low a cooking-heat level as wanted for gentle simmering and suchlike (something even gas is not always good at). Someday, perhaps not so many years away, the world will look back on cooking with gas as we today look on cooking over a coal-burning kitchen stove.

No Wasted Heat

With induction cooking, energy is supplied directly to the cooking vessel by the magnetic field; thus, almost all of the source energy gets transferred to that vessel. With gas or conventional electric cookers (including halogen), the energy is first converted to heat and only then directed to the cooking vessel--with a lot of that heat going to waste heating up your kitchen (and you) instead of heating up your food. (The striking image at the left shows how precisely focussed heat generation is with induction--ice remains unmelted on an induction element that is boiling water!)

As a comparison, 40%--less than half--of the energy in gas gets used to cook, whereas with induction 84% percent of the energy in the electricity used gets used to cook (and the rest is not waste heat as it is with gas). There are two important heat-related consequences of that fact:

• 

  cooler kitchens: of course the cooking vessel and the food itself will radiate some of their heat into the cooking area--but compared to gas or other forms of electrically powered cooking, induction makes for a much cooler kitchen (recall the old saying: "If you can't stand the heat, get out of the kitchen."); and,

• a cool stovetop: that's right! The stovetop itself barely gets warm except directly under the cooking vessel (and that only from such heat as the cooking vessel bottom transfers). No more burned fingers, no more baked-on spills, no more danger with children around. (The photo at the right--one of several similar ones to be found on the web--shows, like the one above, how only the cooking vessel does the actual cooking.)

Safety

We have already mentioned that the stovetop stays cool: that means no burned fingers or hands, for you or--especially--for any small children in the household. (In the image at the right, you can see a pot boiling water on an induction unit while a dollar bill between the pot and the cooktop surface is unsinged.) And for kitchens that need to take into account special needs, such as wheelchair access, nothing, but nothing, can beat induction for both safety and convenience (see the paragraph farther below).

Furthermore, because its energy is transferred only to relatively massive magnetic materials, you can turn an induction element to "maximum" and place your hand flat over it with no consequences whatever--it will not roast your non-ferrous hand! (Nor any rings or bracelets--the units all have sensors that detect how much ferrous metal is in the area that the magnetic field would occupy, and if it isn't at least as much as a small pot, they don't turn on.) And, while an element is actually working, all of its energy goes into the metal cooking vessel right over it--there is none left "floating around" to heat up anything else. (The image at the left shows a hand--wearing a metal ring--harmlessly touching a full-on induction element, while a metal utensil lies equally harmlessly on another, emphatically demonstrating those points.)

Moreover, gas--induction's only real competition--has special risks of its own, not all of which are as well known as they perhaps should be. While the risk of a gas flame, even a pilot light, blowing out and allowing gas to escape into the house is relatively small, it does exist. But a much bigger concern is simply gas itself, even when everything is working "right". Use any web search engine and enter the terms gas health risk cooking and see what you find (really: do try it right here); if, for example, you visit the Gascape web site, you may never again want to even enter a house with gas laid on (take some time to really poke around on this site--you may be shocked). And, of course, all combustion releases toxic carbon monoxide.

Ease and Adaptability of Installation

Unlike most other types of cooking equipment, induction units are typically very thin in the vertical, often requiring not over two inches of depth below the countertop surface. When a cooking area is to be designed to allow wheelchair access, induction makes the matter simple and convenient. (In the image at the left, notice how the induction cooktop is scarcely any thicker than the actual countertop.)

Ubiquity

It is an obvious but still very important fact that induction cookers are powered by electricity. Not every home actually has a gas pipeline available to it--for many, the only "gas" option is propane, with the corollary (and ugly, space-taking, potentially hazardous) propane tank and regular truck visits. But everyone has clean, silent, ever-present electricity.

Cleanliness

Burning gas has byproducts that are vaporized, but eventually condense on a surface somewhere in the vicinity of the cooktop. Electrical cooking of any kinds eliminates such byproducts.

Unfavorable:

The Cooking Vessels

The most obvious and famous drawback to induction cooking has already been mentioned: it only works with cooking vessels made of magnetic materials. The commonest such materials used for cooking vessels are stainless steel and cast iron. Cookware suited for use with induction cookers, from the extreme high-quality end down to thrift-store modest, is readily available; but if you already have a stock of mostly expensive aluminum or copper or glass or pyrex cookware and little or no cast iron or stainless, you might be up for a cookware investment.

On the other hand, if you have a significant quantity of non-ferrous cookware that is not terribly expensive, you can replace it--possibly with much better stuff!--as part of the process; cast iron is by no means "spendy" cookware. If you have ever seen the inside of a real restaurant kitchen, you will surely have noticed that most or all of the cookware is either cast iron or nice, shiny stainless steel (even when they are still using gas for their cooking). Steel is most cooks' preferred cookware material for many good reasons we discuss elsewhere on this site (see the link below--and recall that enamelled steel cookware also works beautifully on induction.

(Note that not all stainless-steel cookware works equally well on induction units; much depends on how the maker has assembled the layers of metal of which the pot or pan is made. Do not assume that all cookware labelled "stainless steel" will work on an induction unit--but almost all makers whose products do work, which includes a lot, will proudly say so in their advertising material or specifications. The easiest test in the world is to take any magnet--a refrigerator-decor type works fine--and see if it will cling to the bottom of a piece of cookware. If it doesn't, or if it clings very weakly, that item of cookware will not work on an induction cooker. If you're shopping for cookware that you want to be able to use on an induction unit, now or in the future, just take such a magnet along with you. Or, if you're buying off the web, make sure the product description says the item is induction-compatible, or ask for a written or emailed statement that it is, with full refund privileges.)

As we noted elsewhere, technology to allow use of any metal cookware--even copper and aluminum--is in the pipeline, but there are definite problems with getting sufficient power levels with that technique, so it will likely be many years before units with it start showing up in the mainstream (if they ever do). So, for now, the need for ferric cookware does remain.

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