Tell me about burner output in induction cooktops

sf7307August 12, 2013

I know when i got my last cooktop [gas], I spent a lot of time on the BTUs -- wanted very high and very low (it didn't work out that way -- I didn't much like the cooktop I got, but I don't live in that house anymore anyway!)

Does the same issue apply to induction? How do the "burners" work --- there's the ones that are concentric circles -- are those just small pan/large pan, or also different power levels?

Here's a comparison I did on AJ Madison of 4 induction cooktops - all are 4 burner, but there's a great deal of difference between the burners and wattage. These are for, in order, a GE, Bosch, Electrolux and KA cooktop. the main difference I see is that the highest power on the Bosch cooktop is 2400, whereas the others are in the 3700/3900 range.

Help, I need an education!

Set 1 QTY 1 1 1 1
Set 1 Output 3700 2400 3900 3700
Set 2 QTY 2 1 1 2
Set 2 Output 2500 2200 3200 2500
Set 3 QTY 1 2 1 1
Set 3 Output 1800 1400 2600 1800
Set 4 QTY - - 1 -
Set 4 Output - - 2000 -

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Xena99

Check out The Induction Site for a good introduction to this subject. There is more to consider than sheer power.

    Bookmark   August 12, 2013 at 3:11PM
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jwvideo

I'll try to give you a summary, but this a subject that has been discussed extensively in other threads. So, read the other threads.

First thing: specs alone will lead you astray into confusion. They get reported differently in different places and mean different things in different contexts.

Second, induction burners are usually paired into zones Typically right and left zones in 30" ranges and cooktops, Each zone has a maximum power output which gets divided between the two burners. Each burner has a "normal" maximum wattage Within that zone, you can borrow power from the other burner and run one burner at higher wattages for a short period of time. This is often --- but not always --- called "boost" or "power boost." Sometimes it is called something else.like power sharing, and sometimes you just have to read a manual to figure out if the burners do this. On some models, the manufacturer may neglect to release the info and it can be hard to find the it elsewhere. Regardless of what it is called, boost allows you to to use one burner to boil water very quickly while the other burner runs at a reduced rate.

So, let's say your induction cooktop has a 1500 burner paired with 2500 watt induction. "Boost" may allows you to "borrow" 1200 "watts" from the small burner and run the bigger one at 3700 watts for ten minutes. Of course, that means you can't do anything with the little burner while the big one is being boosted.

Third, where this gets confusing is that some specs on some sites list max boosted output for each burner, others list max-unbosted output and some list both figures. For example, a "2500 watt" could be a burner that can boost to, say, 3700 watts or it might be an 1800 watt burner that could boost to 2500 watts. Also, when you read specs online, you may one stove maker may be saying that the burner is 2500 watts another saying that its 3700 watts, or maybe something like "3700W (boost)/2500W."

Fourth, the way you find out which figures are being provided is --- well, not always clear. You may find it in the owner's manuals (often available as a pdf download from vendors and from manufacturers' support web sites). You may find it on a specs page on a manufacturer's site. You might have to look elsewhere.

Fifth, at this point, somebody who is is into what I call gonzo searing, will protest vehemently that they don't want no stinking wimpy 2500 watt burners, they need stuff that is always powerful enough to melt lead and they cannot sear a steak unless a cast iron pan is glowing cherry red, so dammit, I want at least a 23,000 btu gas burner which is supposedly "way" more powerful than that puny 2500 watt-hr burner. Well, not so fast. To compare them we need to convert the energy units to from watts to Btu/hr (or vice versa) and we need to take account of the relative efficiency in delivering heat. That is, gas burners put roughly 33% to maybe 40% of their energy into the pans (varies with stove, cookware, burner design, altitude, grate height and other factors.) Induction burners put in between 84% and 90%. So, if you want to compare heat from an induction burner to a gas burner, you not only have to convert electrical energy from watts to BTU/hrs (or vice versa) and then you have to apply the efficiency factor. So, say you want to compare heating from a 3700 watt induction burner to a 22000 btu gas burner. Well, 1 kWh = 3412.14163312794 BTU. So you multiply 3.7 kW x 3412 x .85% = 10,731 effective BTU/hr. Then you multiply 22,000 btu./hr. x 33% = 7,260 btu/hr. Or, to put it another way, to get the equivalent effective energy output from a gas burner, you would need a to be running a gas burner at 32,500 btu/hr in your home kitchen. So, consider how often will you be needing a 32k btu-hr burner for any length of time at home. I consider my own cooking and, with a stove whose burners throw 15k btu-hr, I rarely kick up the heat to max for anything other than boiling big kettles of water. YMMV, of course.

Now, let's go back to that burner at its unboosted "normal' 2500 watt setting which you can run for as long as you want. Remember that a 22000 btu/hr burner has an effective heating power of 7,260 btu/hr? Do the math on 2.5 kW x 3412.14163312794 x .85 and you get 7250 btu-hrs. Darn close, ey?

So, is that powerful enough for you?

Sixth, you asked about concentric rings on induction cooktops. That is sort of related to "large pan small pan," but maybe not quite the way you may be thinking about if you are used to radiant electric smoothtops. With radiant smoothtops, the rings represent portions of the burner. So, you've got a small pan, you turn on only the small portion of the burner. With induction, the whole burner comes on but only the magnetic base of the pan heats. (In effect, the pan is heating itself.) This is often called pan-sensing, but really, pan sensing is just the term for the minimum amount of mass needed for a burner to function. In a sense, the mass of the pan affects the power levels because, when you have a smaller pan, you are using less of the magnetic field than with a pan sized to more closely matches the burner size. (You do understand that induction burners use magnetic fields to induce heat in the pan itself?) But this rarely is an issue unless you need to extreme heat to, say, melt lead in a 3" diameter steel measuring cup. If a pan is big enough (has enough magnetic-metal mass) to register with the burner, you can get it hot enough for just about anything most people would want to cook in a small pan.

Seventh, you asked about very low heat. Most induction cooktops are capable of producing very even, very low heat. But, the thing to look for is the number of digital steps or settings for heat levels. Some cooktops have only 9 levels per burner, some as many as 19 or 20. These often represent half steps and give you finer control at very low heat levels. Try googling "induction + gardenweb + ("low heat" simmer "low temp")" and you will find numbrs of threads discussing low heat and simmering on induction stoves and cooktops.

This post was edited by JWVideo on Tue, Aug 13, 13 at 17:27

    Bookmark   August 12, 2013 at 4:30PM
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kaseki

JW: One major nit

The rate of heat emission or heat transfer is typically measured in either watts (for the rationalized mks system of units) or BTU/hr (for the English system of units). The total heat generated, delivered, or whatever you are doing with it over some period of time (the integral of the rate) is measured in joules (watt-seconds), kW-hrs, or BTU. Hence, some editing above is advised to avoid causing confusion with the units.

The hobs are correctly rated in watts, although this is likely watts used by the unit and not watts delivered into a pan, but watts used can only be measured with a pan involved because otherwise the induction magnetic circuit is not complete.

Induction efficiency is relatively high, and probably similar among units, so ratings for the same action, e.g., Power Boost or not, can generally be compared. I second the Induction Site recommendation.

kas

This post was edited by kaseki on Mon, Aug 12, 13 at 19:47

    Bookmark   August 12, 2013 at 6:57PM
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jwvideo

You are correct. Sorry for any confusion. In dashing off a response, I see I did mix things up in describing the units of measurement. When I am being careful and not just dashing off responses, I remember that the equivalencies are watts to btu/hr. and watt-hours to btu rather than the way I wrote it above.

Mr. Chairman, I defer to superior knowledge of the member from California, and stand corrected. ;>)

    Bookmark   August 13, 2013 at 3:27PM
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ginny20

OK, I have to say it because you mentioned Kitchenaid, and I would be remiss If I let someone buy one inadvertently. It clicks! It can be annoying! I love how it functions. It only has 9 power settings, plus boost, but the boost does make water boil fast, I can melt chocolate without a double burner, and I can set a pan on level 1 to keep warm. It has a bridge burner. And of course, it cleans up like a dream. But if you haven't read about the noises it makes, please do before ever considering it.

Here is a link that might be useful: Noisy KA induction

    Bookmark   August 13, 2013 at 3:51PM
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kaseki

NH -- Nearly as laterally and philosophically distant from California as it is possible to get in the USA.

kas

    Bookmark   August 13, 2013 at 9:10PM
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