I think you are also asking about the differences (pros and cons) between rangetops and cooktops, right? Surface area - cooktops have less real estate for your pots and pans because of the knobs. If you are looking at a 30" cooktop, this is really a problem (see Deeageaux's pic above), and I would not recommend a cooktop in a 30" size. Rangetops have the knobs across the front, like a range, but without the oven, so more surface real estate for your pots and pans. Aesthetics - cooktops are a more sleek contemporary look; rangetops are a more "professional kitchen" bulky look. A matter of personal preference. Power - rangetops tend to have more btu's than cooktops, though many find the cooktop's btu's to be plenty, so again, personal preference. Knob placement - for cooktops, some say they don't like the idea of having to turn knobs while a hot pot and flames are right next to the knobs. Also there have been reports of cooktops' knobs becoming damaged over time by the heat. Others say they prefer the cooktop's knob placement because it's easier to see them (vs. looking at the knobs on a rangetop), and they don't mind that the knobs may or may not be close to heat. Future replacement - if you need to replace a rangetop, it's a matter of simply switching out. If you need to replace a cooktop, you may or may not find another cooktop with those exact dimensions to fit in your counter cut-out. This problem has been reported several times on this forum and the Kitchens forum, with people having to re-cut counters or find filler for counters in order to fit a new cooktop. Expense - rangetops cost more than cooktops.

I would recommend a 36" cooktop 100% over a 30" cooktop. The reason is that in a 30" size, the knobs on the cooktop will take up valuable cooking space. Please visit an appliance store and check out any brand's 30" cooktop, and you will see what I mean about the knobs on a 30" cooktop. There is very little room left for a larger fry pan or pot when you lose those inches from a 30" cooktop to make room for the knobs. I do not entirely agree that a 36" cooktop requires a 42" vent hood. It's a nice-to-have, but you will be fine with a 36" hood. Just make sure the hood is deep enough to exhaust the front burners (i.e. don't get a hood that is shallow from front to back, even if it's a bargain). Another alternative if you do not want to lose valuable countertop space to a 36" cooktop, is a 30" "rangetop". A rangetop is basically the top part of a range, without the oven underneath. That means the knobs are across the front, like a range, rather than taking up valuable cooktop space. Another advantage to a rangetop is that it will be easy to switch out to another rangetop in the future if need be, cause there is no countertop cutout. A cooktop on the other hand, has a countertop cutout specific to that particular cooktop. Should you need to switch out the cooktop some years from now, it will be very difficult to find a cooktop with that exact cutout to fit. We have seen that situation several times on this forum. And, many people prefer the more "professional kitchen" look of a rangetop, but that is individual taste. The disadvantage to a rangetop is that it is more expensive than a cooktop. Here is a link that might be useful: Kitchenaid 30-inch Rangetop (Looks like there are rebates available from KA right now!) This post was edited by alwaysfixin on Sun, Dec 16, 12 at 12:32

I have a 30" gas range with five burners. It's possible to use all five simultaneously if you use mostly small pots. If you want to cook a gourmet dinner for two, the fifth burner might come in handy. If cooking for four or more people, you probably won't have room for a fifth pot.

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