Image Credit: Marc Rosenbaum
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We don’t often think about the energy we use for cooking. In the most economically disadvantaged countries, gathering energy for cooking is a major component of people’s time (mostly women), and smoke from wood cooking fires is a significant health issue. One great solution for these people is solar cookers, and this organization is my favorite non-profit, because it helps the planet’s poorest people while doing environmental good.
In industrialized countries, cooking energy is off our radar. We first started thinking about it seriously when Jill got the book by Kate Heyhoe called Cooking Green. The authordescribes a lot of simple techniques to reduce cooking energy. Reading this book, though, pushed me to try a technology I’d heard of before but associated with very costly appliances, the induction cooktop.
Gas stoves aren’t very efficient
Gas cooktops place a flame beneath the cooking pot, and heat up the bottom of the pot, which transfers heat to the food within. A conventional gas cooktop is a tad less than 40 percent efficient. You can sense this because you can feel the heated combustion products rising around the pan, and often the handle of a fry pan gets too hot to touch when used on a gas cooktop.
Gas also has the disadvantage of creating these combustion products in your kitchen. Harvard School of Public Health’s venerable Six Cities Study is one of the research efforts that has linked gas cooking with increased respiratory symptoms in children. When I use a gas range or oven I always use the range hood if one is available, to exhaust at least some of these pollutants outdoors.
Nonetheless, gas has always been the preference of the serious cook (and wanna-bes) and certainly in high-end homes there has been a proliferation of commercial-like ranges the size of Mini-Coopers with associated commercial-like range hoods which suck pets and small children right out of the kitchen. Gas cooktops are preferred over electric cooktops because they can be turned down quickly.
Traditional electric cooktops are more efficient than gas — about 70 percent — but the thermal mass in the burner has made them slower to respond than their combusting competition. There are more modern electric burners like halogen cooktops that are speedier, yet, like the gas cooktops, they heat the pot which then heats food.
An oscillating magnetic field
Induction cooktops work by inducing a current in the piece of cookware with an oscillating magnetic field. The resistance to this current flow creates heat. The energy is delivered directly in the pot without first heating it from the outside, so it is both fast and efficient — efficiency in the mid-eighties is often cited. Using an induction cooktop limits your choice of cookware, because it has to be ferrous: iron, steel, or some kinds of stainless steel.
We got interested in trying an induction cooktop and learned that single-burner units were available on eBay for under $100. We bought one sold by Burton that was rated at 1,800 watts, about as large as is possible to use on a 120-volt circuit.
We began to experience the benefits although there were drawbacks, too — this particular unit has a cooling fan and is a bit noisy. It was, however, almost instantaneous in its turn-down of temperature — you could have a rolling boil and hit the controls and bingo — it was simmering or less. And if water boiled over onto the cooking surface, it didn’t even sizzle, because the heat is generated in the pot, not the cooker.
It was time to get rid of the old gas range
When we moved to our current home, we inherited a KitchenAid gas range. I thought it was surprisingly slow to bring large pots to a boil, and I disliked having to use the noisy range hood every time I was cooking.
We began to look for electric ranges with induction burners. One of the least costly was this Frigidaire that had the intriguing (and money-saving) feature of having two induction burners and two conventional electric burners, all beneath the same glass top. You can keep all your cookware because the non-ferrous stuff is usable on the conventional burners. We ordered one.
The large induction burner is over 3,000 watts and is the fastest burner I’ve ever used. I cooked eleven pounds of potato salad in two pots a few weeks ago, putting the larger pot on the induction burner and the smaller one on the conventional burner. The spuds on the induction burner were done before the other pot came to a boil.
When you get a higher-end appliance like this one, you get the good with the bad. It’s all digital push pad rather than nice analog twisty dials — I hope the digital brain lasts a long time.
On the other hand, it has convection oven modes, and lots of cool racks. The conventional burner side has the nifty feature of a “bridge” burner between the two round burners, which can be used to apply even heat to a griddle that straddles the whole side of the cooktop. Great for pancakes and French toast.
Our new stove uses a fraction of the energy of the old one
I have a pretty good idea of how much energy we used in the gas range, because for several months our only gas appliance was the range. From a delivery on September 27, 2010 until we installed the new electric range in early April 2011, we used about 13 gallons of propane, or 2.1 gallons/month. That’s a gross input of about 192,000 BTU/month.
I have a kWh meter on the electric range, and in four months it’s consumed 51 kWh, which works out to 174,000 BTU in total, or about 44,000 BTU/month. That’s twenty three percent of the gas range consumption. If primary energy is accounted for, the new range is using about 60% of the primary energy that the gas range did.
In addition, the lack of combustion means that we only use the range hood when we have odors or excess moisture — not as a matter of course. This will save heating energy in the colder seasons.
Overall, we think the induction range is the bee’s knees. South Mountain Company has put a couple of them into custom homes, and the owners love them, both for their cooking speed and controllable output, and for the health benefits. And apparently more and more professional chefs are turning to induction, so they are in good company.
Marc Rosenbaum is director of engineering at South Mountain Company on the island of Martha’s Vineyard in Massachusetts. He writes a blog called Thriving on Low Carbon.
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23 Comments
Convince my wife
Now if I can only convince my wife...
Time for Induction
I'm in exactly the same place you were ... Testing with a single burner Burton before making the plunge for the big induction cooker. I buy foreclosed homes and fix them up greener than new codes. But so far, I've yielded to the "Foodies" who all say they want gas. However, now that I am renting them out instead of flipping them, I will begin putting in induction cooking. Perhaps include a set of cookware as a move-in incentive. Based on my experience with my single induction burner, I'm sure they will love it after they try it. In sales, it's called the "puppy dog close" And it's how I started putting Mini Split Heat Pumps in all my projects. After the buyer or tenant tries them ... they all love them. So I'll be looking for the best entry level induction cooker for my renovation projects and I think I'll go for that unit you mentioned for my house. Thanks for the review to push me off the fence and go ahead with what I had already planned.
Induction concerns
The big concerns most foodies have with induction cooktops are use of cast iron and wok cooking. Cast iron has a tendency to scratch ceramic/glass cooktops pretty quickly, and given the weight of cast iron pans, they aren't always lifted straight up and down. Well maintained cast iron pans are almost certain to outlive you, your induction cooktop, your house and your kids.
Wok cooking is the other issue, although I saw an induction wok cooktop burner in an ad for a diy network show about KBIS this weekend.
Things to think about.
Terrific.
This is something I've really been wondering about. Now if I can just (a) convince my wife, and (b) figure out what to do with my new 18/10 stainless steel pots. Thanks for posting, and for the links.
Induction Cooking
Marc, you overlook an important energy issue associated with induction cooking - peak demand. As an electric device, induction cooktops have large peak demands. Althought data is sktechy from the manufacturers (most sales reps I've talked to look at me with rolled yes and start talking about how you can touch the surface when I ask the question), the data I've been able to collect on induction cook top peak demand is scary - up to 10 kW per burner. This is a serious issue for us utlility types, and has serious implications for residential energy use. Yes, you can cook something faster and without the combusition issues associated with gas stoves, but you can't escape the fact that induction cook tops are electric devices that have large peak demands. With the introduction of time of use rates and smart metering by utilityies across the nation use of Induction cooktops also has serious utility bill implications. You can also imagine how the high peak demand of induction cooking might affect use of PV. In brief, you'd have to install a pretty big PV system to meet the instantenouse power needs of induction cooktop, especially if you're using more than one burner (think Thanksgiving or a party). As a result, I don't recommend use of induction cooktops in the ZNE demonstration projects I work on.
Full disclosurer: Mike works as a research project manager at the Sacramento Municipal Utility District (SMUD), a publicly owned electric utility.
Response to Mike Keesee
Mike,
Do you have evidence that induction cooktops have a higher peak demand than ordinary electric-resistance cooktops?
There is an apparent contradiction here: Marc is implying that these stoves use less energy than other cooktops -- and I assumed that he meant that they use less energy than electric-resistance cooktops.
Since electric-resistance cooktops are very common, and since utilities haven't been brought to their knees by electric-resistance cooktops, why the fear about induction cooking?
My Perfect Appliance
We have a GE Profile stove. It has halogen burners on top, but has a two part oven. A small pizza oven and a larger lower oven. We cook almost everything in the smaller oven, but when the boys come home we can use the larger oven.
I want an induction top with a two part oven. That would be the perfect stove. A slide in universal easy replacement for electric and gas stoves.
Response to Mike Keesee
Mike,
I think you're way off on your numbers. I just looked up a "high-end" Viking 6-burner induction cooktop and came up with a maximum of 13.5kW total based on their specs (240V x 56.3Amps)....and that's only if you have all 6 burners at 100% power.
I'm not sure if Marc R. is data-logging instantaneous power, but hopefully he is and can provide some good data on this from his house. I can give you a general idea though based on my house (plus-energy house in central Virginia...with well-used induction cooktop), since I can get energy usage history in 30-minute intervals from my electricity provider. Over the past 2 months, my peak 30-minute usage from the grid was 2.4kWh (4.8kW) for the entire house (this happened between 5:30pm and 6:00pm). My average peak demand from the grid (30-minute interval) for the past two months during the 3:00pm to 8:00pm hours of the day has been 0.6kW (of course, we are sending energy into the grid during many of these hours). We have a 6.2kW PV system and don't have TOU metering.
Awesome cooktops, but get an extended warranty!
We loved our induction cooktop (an Electrolux) until it failed. It's way faster than any gas stove (let alone other electrics) and since the top doesn't get hot food doesn't burn on it the way it does with smoothtop electrics. But ours failed after just a year of use and the estimated repair cost was close to what we paid for it on Ebay ($1250). Fortunately we bought a SquareTrade warranty and they send us back our purchase price, so we're only out $80 for the service call and $50 for the warranty. Be sure you do the same if you want to join us out here on the bleeding edge. I also now recommend the same with front-loading washers (just had our Maytag fail a month out of the one-year warranty, and although they did offer to cut the repair cost 50%, that's still over $200!).
Oh, and they do require more power, at least on a per burner basis. Ours had 2 burners of 3600 watts, which is 50% more than the biggest smoothtop I've seen (it requires a 50 amp breaker and the separate ovens another 40 amp breaker). Of course, because more of that energy goes into the pan instead of into the air you use it at full power for far less time so there is a net savings.
beware phantom loads
An induction cooktop that we installed for a client peaks at about 2.5 kW when in operation, just for general background.
But it appears to be using about 40 watts in stand-by mode, which is about 350 kWh a year. In the couple of months we've been trying to trouble-shoot this, the manufacturer's tech support has been often friendly and accommodating, but fundamentally useless. First they said it was normal, then they said it wasn't, when Martin blogged about it.
I think they don't really care, in the end. So be sure to ask you supplier what the phantom load is for the appliance you're considering. They won't be able to answer, but if enough of us ask the question, maybe one day they will.
Response to Paul Eldrenkamp
Paul,
You raise the nerd's lament: "The manufacturer's tech support has been often friendly and accommodating but fundamentally useless."
I want that on a T-shirt...
For once I'm in complete agreement...
I think induction is the bees knees and wish I had one. I'm similarly attracted by the idea of a "hybrid" cooktop, half induction and half halogen. I too enjoy the square griddle bridge burner feature of our present all-halogen range.
I'm really tired of otherwise-sane energy / green clients who insist on gas cooking. Here in sunny Florida, gas cooking adds yet more heat to reject via air conditioning. Not mentioned so far here is the devilish addition of latent load - combustion of gas yields water vapor, the last thing we need 9 months per year in a Florida home.
I have a new construction client who insisted upon a 48" Viking (Mini Cooper Special) range, a 1200 CFM hood and not one operable window in the kitchen or even within 30 feet of the kitchen. There is a fireplace, though, and the house is quite tight, so I'm quite concerned about backdrafting.
Icing the cake, the owner intends to rent out the house...will clueless tenants have any idea of the danger posed by a huge hood, un-openable windows and a fireplace?
Back to the matter at hand - per my TED, our conventional double oven halogen range used 14 kwh last month, or 48 kBtuh, similar to Marc's reported usage. We don't eat out much, but I suspect the toaster oven and microwave figure in a bit as well. Eventually I'll log those loads as well.
I hope the guy all wound up about induction peak loads doesn't dry laundry with electricity...the typically electric clothes dryer smacks the grid with over 5500 Watts continuous load for at least 20-30 minutes 4 - 8 times per week.
I am on a tear this week about phantom or vampire loads. A range using 40 Watts in standby (mine uses 1) would burn 29 kwh per month, double what we used actively cooking...that's completely unacceptable.
I love my induction cooktop
We built a new house last year and I, too, almost yielded to the "foodies" who were snobbish about gas. With no room for a hood, I considered gas without a vent but my inspector warned me of the dangers of indoor air pollution. He said almost 80% of homes he inspects with gas stoves are not vented to the outdoors, they just have "faux" vents with recirculating fans and filters. No wonder so many people have respiratory issues. So, I went for the induction and chose a 30" Kenmore cooktop - rated one of the best and most economical. It took a while to figure out how to use because it's so darn fast and wickedly powerful that I have to have everything ready to go before turning the stove on and I burned a lot of things for the first few months by turning it up too high! My favorite pan is an old cast iron skillet and I can cook eggs in a few minutes (that includes heating the pan) and have the pan and cooktop wiped down in 30 more seconds. Try that with gas! Or, easier yet - I use oven parchment paper under the pan (no, it doesn't burn) and then I can slide the pans around without scratching the cooktop or having to clean it due to drips and splatters. I also read somewhere to sand the bottom of a cast iron skillet to make it smooth so it won't scratch when sliding it. Actually, it took me a while to stop sliding pans off of an element- - like we all do. I had to re-train myself to simply leave it where it was and turn down the dial. It **instantly** responds. I recently used my parents gas stove and couldn't believe how long I had to wait for water to boil and the time it took to clean the gunk from the grates and burner pans. ugh. Right then, I realized I will never go back to gas. Gas gives off more heat, odors and steam. Induction gives off virtually no heat and no residual soot either. Our unfinished drywall backsplash is still pretty clean after a year. Now for the drawbacks I have discovered: My 30" cooktop (most are the same) is laid out weird, the elements are squished together which make it hard to fit multiple pans on it. It's because all of the controls run along the bottom plus they beep if you lay a lid or utensil on them which is annoying. Some of my light-weight pans make a buzzing noise when in use which I found out is due to the construction of the core in the bottom of a pan. (Induction works by resonating a frequency and some of the metal cores rattle which sounds like a buzz!) Also, make sure the pan bottoms are very flat - it has to make contact to work. Another negative I can say, my cooktop is shiny black and it takes a lot of polishing to keep it streak-free. I would look for a 36" with the controls on the side or grouped in the middle with a better element layout -- a griddle bridge would be great. Plus, one with a pattern on the glass to keep the scratches and streaky top hidden. And, a tech told me these induction cooktops aren't very popular because they are all electric and when they break, you almost have to start over because they are very expensive to repair. That brings me to my last point - I would stick with a separate cooktop and separate oven for not only ease of future replacement (and cost) but I fear that an induction top with a built-in oven below wouldn't be able to cool off as well and lead to premature electrical failure. Mine has an automatic fan to cool it down and requires a clearance underneath. Additionally, find a brand with a long warranty and/or extended service plan.
I enjoy still being able to
I enjoy still being able to cook when the power is out. That most recently happened two weeks ago. My grid-tied PV would have been of no help with an induction cooktop. Thanks, gas.
But the day I'm convinced my cast iron won't scratch it up, I'd probably give it a shot.
Induction cooktops are
Induction cooktops are gaining popularity in commercial kitchens, but mostly for back of the house food prep. I interviewed a chef in Chicago last year who was thrilled with the performance. They can be fine tuned to precise low temps for "sous vide" and tempering chocolate without additional equipment and minimal effort, something gas or electric cannot do. But they are most often used for pasta stations or cooking stocks, which require long cooking times.
For commercial kitchens, the energy savings do not come from the hobs themselves, however. The savings come from being able to reduce the cfms in the ventilation. A commercial kitchen using a six burner induction range can reduce ventilation from 4700 to 1900 cfm because the overall temperature in the kitchen is reduced and less conditioned make-up air required to replace outgoing flow. For residential use those numbers won't be so significant, but they could add up.
I'm surprised no one has mentioned the elephant in the room, EMF exposure. Studies such as this one http://www.ncbi.nlm.nih.gov/pubmed/22674188 have shown that the hobs can exceed levels generally considered safe by European standards (at least at close range), so it might be best to keep the kids and pregnant moms away from these and use them for your potatoes and stock and not for something requiring constant stirring. Still, I wish I had one!
If you're stuck with a gas stove, check out http://theturbopot.com/. They use heat fins to improve heat flow to the pots/pans. They are supposed to work great, dramatically reducing cook times.
Response to Minneapolis Disaster
We use cast iron (two 10" skillets and one 15" skillet) for more than half of our cooking. No scratches, yet, on the glass cooktop after 4 years. We don't shake our pans around a lot though. Gotta be careful when lifting the 15" skillet...that thing is a beast.
IAQ Issues and induction cooking
Two comments. First, I have done stovetop testing for ultrafine particle emissions and found that during water boiling test, induction cooktops were the only ones to not emit significant UFP (both gas and resistance did). This is a major benefit of this type of cooking, as cooking activities dominate indoor UFP levels. Second, Marc your range hood is NOT only for combustion byproducts, but also removes pollutants that result from the actual cooking of food. This is why electric ranges still need to be vented. Particulate matter, formaldehyde, acrolein and other pollutants are still emitted at high rates. Please do not recommend not using the kitchen extract fan.
I guess I have a 3rd comment about your primary energy estimate for the induction cooktop. What conversion values are you using for propane and electricity? I ask because the source energy and carbon intensity of electricity use is very high in some parts of the country, and an induction cooker would have to use anywhere from one half to one fifth the site energy of a gas cooker in order to just break even...but I don't know about these values for propane. Seems to me that it would be similar to natural gas?
Whoops primary energy foible
I was looking at the total induction BTU and comparing to monthly gas number. Whoops! Still, in many parts of the country electricity is more than four times worse than gas, which again leads to only breaking even...or worse. If you previously cooked with resistance, then induction is an amazing improvement. Or if you live somewhere with low carbon electricity (Washington, Oregon, Idaho, CA, VT, etc.) Its also a big win.
I convinced my husband
In our house my husband does most of the cooking. After much research, discussion and an in store demonstration he was convinced that an induction cook top was the appliance to use in our new near passive house. You can get induction ready cookware at Marshalls for the same or lower cost as regular cookware.
Reply re. Extended Warranty
This thread is pretty much defunct, but I thought I'd add one thing re. Scott Raney's recommendation of an extended warranty. The December 2012 Consumer Reports arrived today, and in it (pp. 56-58) were ratings of various ranges and cooktops, including induction units. Induction units were consistently rated the highest in performance, but of equal interest is the fact that CR still does not recommend purchase of an extended warranty for any of the appliances listed, including gas, electric resistance, and induction.
Induction Cooking
I'm glad to see that my comments on the peak demand impact of induction cooking got the juice going.
Martin, in response to your question, I've only been able to get peakd demand information from one manufacturer. In general, sales reps stare at me w/ puzzlement when I ask about the peak demand of their products, and the manufacturers don't publish data. In brief, more data needs to be offered and/or collected. Hey NREL/DOE, is this a research opportunity?
As to the fear question, yes, we in the utilty world (full disclosure, I work for the Sacramento Municipal Uitlity District (SMUD)0 are very concerned about peak demand as it drives our costs and is a major contributor to local air pollution when utilties fire up "peakers."
In response to Mr. Semmelheck, 13.5 kW of potential peak demand is scary. FYI, utility resource and distribution planners always plan for worst case. So add that 13.5 kW of stove to the AC to the rest of house and you might have 1 or 2 houses per 50 kVa transformer. For years, we in the efficiency side of the business have been trying to convince our resource and transmission and distribution collegues to downside infrastructure based on the reduced home loads. Now you've just added 13.5 kW to the house! Oh, by the way, you're PV system doesn't count in the resource/T&D world because it's 1) not reliable (think clouds) or 2) dispatchable (see reilable). Finally, 2.5 kW peak is a big deal. I'm trying to convince folks to go zero peak and to do so with the minimum amount of PV becasue, well, PV's expensive, still.
Mssrs. Eldrenkemp's and Less's comments on stand-by loads and source energy impacts of induction cooking are on point, especially the source energy impacts. Remember, we're still dealing w/ electricity here with all the associated losses found in the grid.
Mr. Kinler's comments are on point about electric driers. That's why I encourage participants in our programs to install gas clothes driers. However, if push comes to shove, utilities can control clothes driers. We could easliy develop demand response (we used to call them load control) programs for driers and offer incentives for folks to re-schedule their clothes drying to off peak periods (which, by the way, we in the utility would prefer... think kWh sales and revenue). Being able to "manage" customer demand is a very important point becasue theoritically we could control or lock out use of the induction stove during a utility peak period, but you could imagine the howl (and rightly so) from our customers -- i.e., you're telling me when I can eat?!
All that said, I do know a place where induction (electric) cooking has made major inroads - Japan. But you need to look at how electric cooking has come to predominate in Japan, which are largely cultural and safety issues. First, the Japanese don't have big stoves or for that matter do a lot of cooking at home (think of Salary Man eating out every night), and rely on smaller appliances (rice cookers and the like). They also tend to eat later in the day then we do (when it's a little cooler). Second, they have this well deserved phobia about gas - gas pipleiines tend be break and explode in earthquakes (I think most gas use in Japan is done w/ propane tanks; at least that's what I saw when visited).
So a word of caution about induction cooking. Yes, it's better than resistent cooking, but not much, espeically from a peak demand point of view.
@mike Are you talking inrush current?
I have read this article and your comments and I have looked at the loads of induction cooktops. They do have high wattage elements, and considering inductive loads have high inrush currents I would think that inrush to a 3 Kw induction driver could be 3 to 4 times that 3Kw. That would only be for about 20 msec. The chances of everyone turning on elements at EXACTLY the same time is very remote. The thing I would worry about is the magnetic field if you have a pacemaker.
Induction Cooking response to Roger Williams
I'm referring to instantaneous peak demand. Keep in mind that utilties across the nation are installing "smart meters" (my employer/utilitiy has completed its smart meter change out) and smart meters have the ability to recording use to the minute (or finer). Installation of smart meters will lead to time of use billing with the potential for demand billing. So if you use your induction cooktop for only a minute (or maybe less), a smart meter will capture the instantaneous demand in kW, and in the future you might get a bill from your local utility based on your energy (kWh) use and peak demand (kW). As a result, I don't recommend induction cook tops in my zero energy projects.
Oh, did I mention that they're really expensive and require 220 volts and maybe an upgraded electric panel?
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