We initially planned to have our cooktop be a series of these modular cooktops. They look very sleek, but I discovered that no one manufacturer had top power options in all modules. The only way to get the best induction or the best gas or the best wok burner is to mix & match among Wolf, Gaggenau, & Thermador, and we didn't think that would look very good. Some have controls on the front (like a rangetop) while others have them on top, stealing room from the cooktop. Also, the total number of possible burners comes out to be less than a conventional cooktop, and the price is quite a bit more. Since we already had a hood planned for a 60-66" cooktop, we then considered other options, including one 60" or multiples. DH wanted gas, I wanted some induction and a powerful wok burner. Here's what we finally decided to do: We flanked the DCS 36" all gas range with the Gaggenau induction cooktop and Gaggenau teppanyaki. The Gagg induction is capable of at least 30,000 BTU & is a great wok burner.

The reason the manufacturers say not to do it is that they want the bottom of the pot to be in contact with the surface of the cooktop. Some units won't even register a channel bottom or one with a lip. Others will register and heat them, and work within a quarter inch of the surface, though perhaps not as efficiently. I have used my Graniteware roaster with the tree dents on my 11" element to make gravy, and that works just fine (lots of questions have been asked about that!), but canning is another story. What concerns me, though I haven't had a chance to ask the manufacturer of my induction (Gaggenau), is that the air in the space under the canning pot (or my big griddle) could get extremely hot, and if it's damp, steamy. This might just be a safety issue to be aware of when moving the pot. But I worry that a sufficient volume of super hot air could crack the glass. My unit does have an over heat sensor though, and the unit will cut off entirely during marathon stock making sessions (11" flat bottom, Le Creuset, enamelled steel stock pot). I don't know if that kind of overheat will happen to you with your canner. I was simmering pretty high with a turkey carcass when that happened to me. I don't think it did when I made chicken stock, which I think simmers lower. Keeping a full sized canner on the boil for a long time will probably trip the sensor as well. If you're just doing a seal on jam, it should probably be fine, but might not work for a long boil. I can't imagine the weight being too much (unless it's dropped) or the enamel melting. Enamel is glass based. It melts a temperatures that aren't allowed in home kitchens, like over 1500 degrees. A bigger issue might be the diameter. I think even the small Graniteware canner is a few inches bigger around than your element. I don't know if that is more likely to lead to cracking or something. Generally, you're expected to use a pot that's no more than an inch beyond the ring (two inches more in diameter). People here have mentioned issues with pressure canners and induction, but you need an awful lot of ooomph with a pressure canner, and the heat might cut out before you develop enough pressure. Do ask the manufacturer. You're more likely to get a good answer. I'd do it in writing, by e-mail, so they can have a good discuss rather than having a customer service rep give you a canned answer. (so to speak)

Of course it is "possible." Just like Dr. Frankenstein worked at home. Whose project, echoing the question by gigleus, had some major reliability and safety concerns, to say the least. Maybe, more like the kind of "home brewed" projects such as, say, turning a 20 year-old pickup into an all electric vehicle or into a dragster with a twin supercharger "454" motor and huge racing slicks, or turning it into a four-wheel-drive, high lift monster truck. Can be done, but would you want that for your daily ride? Hvtech has an interesting suggestion for owners of old Jenn Air "modular" cooktops and stoves. However, while Jenn Air made numbers of smoothtop radiant electric cartridges/ modules, I cannot recall ever seeing an induction cartridge. The burner control systems were just too different, which is a big reason why nobody makes (or will make) plug-and-play induction modules that can fit into the top of a coil-burner stove or into the supports beneath an old smoothtop. The older style electric stoves used electro-mechanical potentiometer/rheostat burner controls. Making those work with the digital microprocessor controls used by induction burners is pretty complicated. (AFAIK, only Miele and Garland/Mantowiac induction burners have potentiometer controls; their products cost $$$$) This is what Homepro meant with the comment about different control technology. For a Frankenstove, you would need to rip out the old control systems and wiring, assemble a set of the microprocessor-driven control-boards required to operate the induction burners, and then figure out how to reprogram them and convert them to work with a rotary knob interface. You also would need to build a fan system to keep the induction electronics cool, which is something nobody did with electric stoves 25 years ago. You'd also need to build in enough space for clearance from the oven part, too. All of that would be for naught if your old stove has the oven vent in one of the rear burners as numbers of electric coil stoves did, back then. The closest thing to "plug-and-play" induction burners are the commercial "drop-in" induction burners from the likes of Cooktek. In theory, you could carve up or build a new stove-top to hold four of them, rewire the range, and cut holes in the backsplash to mount their control modules. That would cost you around $4k to $5k in parts, which is a whole lot more than just buying a new induction range outright. For that kind of money you might as well be looking at the ultra-premium priced induction ranges from the likes of Dacor, Viking and Miele. And a Cooktek style solution would still require you figure out how to get enough clearance below the burners for their cooling to operate while you are using your old stove's oven. So, no plug and play solution here. As homepro noted, some folks have pulled out old non-functioning coil burners and placed a couple of portable induction cookers (PIC) over the holes, That will raise the level of your cooking surface by two or three inches which may or may not be a problem. The size of the PIC casings is large enough that it will be next to impossible to fit more that two PICs on top of the old stove. Depending on how many burners you use at a time, that may or may not be a problem, as well. There are some limitations to working with the less expensive PICs (which would be most of them). In an older kitchen, there might be some problems finding enough separate 120v electrical circuits (PICs can draw so much current that you will blow a circuit breaker by running two on the same circuit at the same time -- same thing with a microwave, btw). One nice thing, though, is that many electric stoves from 25-years ago had an extra-120v outlet on the backsplash and, running through the stove's connections, that outlet will be on a circuit separate from other kitchen outlets. If that kind of solution interests you, you could check out the discussions in the cookware section at chowhound.com where numbers of folks like paulj and have reported putting PICs on old stoves and several others have decided to dispense with stoves altogether. Also, look over the blogs on induction at www.centurylife.org. For a discussion here on using PICS, you might check out this thread if you have not already seen it: http://ths.gardenweb.com/discussions/2324992/portable-induction-cooktop-and-cookware

I bought a second-hand 4 y.o 30" Bosch 800 series: NIT8066SUC (Stainless rim on top and bottom) for a fraction of a new Bosch cooktop. The control on it is easy to use: it depicts 4 separate icons representing the burners that you select before using the single universal power bar. We use either a paper towel or parchment paper to prevent scratches under our cast iron skillet on the highest heat to sear meats. The paper towel does have brown markings, but has never burned. I like MizLizzie suggestion of a thin silicone protection pad; I'll look for one to try. We used inexpensive single countertop induction plates for 4 months before deciding to get the Bosch to replace a broken 20 yr old 30" electric radiant. Still love it after 2 months of solid use by 3 members daily.. No complaint by 30 - 60 y.o hearing of very low level almost undetectable hum/sound