Cookin'

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. She describes 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 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 ro 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.

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 1,800W, about as large as is possible on a 120V 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, amost instantaneous in its turndown 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.

When we moved to House 5, 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 kW 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, 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.

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 9-27-2010 until we installed the new electric range in early April 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 sixty percent of the primary energy that the gas range did.

In addition, the lack of combustion means that we use the range hood when we have odors or excess moisture, but not as a matter of course. This will save heating energy in the colder seasons.

Overall, we think the induction range is the bees knees. South Mountain has put a couple 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.

Comments

[Andrea Lemon]

Thanks for the summary. You turned Ted and me onto induction cooking when we first met you -- we now have a wimpy 1600W mini-burner in our apartment, and it's wonderfully responsive. It's perfect with our pressure cooker. Two of the biggest foodies I know swear by induction cooking, and we are planning to install a 4-burner cooktop in the new house.

Sadly our fancy non-ferrous pots and pans will have to find a new home, but good induction-friendly cookware is not particularly pricey as long as we're not seduced by Williams-Sonoma brands.

[Bob Lemaire]

I like the technical analysis of induction cooking and the whole idea of it has always been so cool to me - if not so much to the cook in the household. As in most of these opportunities that make great technical sense, there has to be a component that attracts the less technology leaning (i.e. average person). You may have hit on it in the ability to boil water very quickly. We have a thermador combination gas/electric cooktop that has three gas burners and two electric. The cook prefers the gas, and uses it exclusively. What I'm wondering is if one or more electric could be converted to induction, and maybe become more useful, at least to boil water. Anybody have any thoughts on that?

[Marc Rosenbaum]

Great question Bob, call Thermador and ask 'em!

[Adam H]

I've been coveting an induction top for a while, now, so this was a nice bit of analysis to read. I feel compelled to point out, though, having read the Fridgidaire page: They claim your oven has a "chicken nugget button." Them's fighting words, where I come from.

[Bob Lemaire]

Well, I did send the question to Thermador, but I seriously doubt they would be interested. If they were to offer upgrade they would be cutting themselves out of an upgrade sale, but more likely, it would not be worth the development cost to get all the approvals they would need. I think I would be on my own to try and fit an induction burner into the unit and wire it to the existing controls. I guess what I was asking you and your followers was, given your experience and research, do you think there would be issues with, for instance, mounting under the glass top, and the nearby cast iron gas burners.

[Marc Rosenbaum]

Well, Adam, I was trying to keep that particular piece of info under wraps but you've blown my cover. We have 25 chicks in the basement right now, and I'm watching very closely to see when I can first begin to harvest some nuggets.

Bob, I know Gaggenau offers modular cooktops that can combine induction, gas, and electric, as well as various other bits. But I know nothing about the prudence of modifying your Thermador.

[j chesnut]

I worked on the design of the Passivhaus in Hudson, WI which included an induction cooktop. I don't have the info handy but the Thermador unit sounds familiar. The project is being monitored for energy use and we seemed to have found that the induction cooktop had a phantom load which we were surprised by because the unit did not have any digital display that was in constant operation. Anyone else experience this or know of induction cooktops that avoid phantom loads?

Reading this post is the first time I've heard of pollutants due to gas ranges. Is this true for both propane and natural gas? I have a natural gas cooktop but I always hear that natural gas burns clean.

[j chesnut]

A correction to my previous response. Just found out today that after the energy monitoring equipment was upgraded and reconfigured there is no longer an indication that the induction stove has a phantom draw.

[About WFG]

Well I must say nice post..Traditional electric cooktops are more efficient than gas - about 70 percent - but the thermal mass in the burner has made them slower ro respond than their combusting competition

[Daniel Bergey]

You're saving much more energy than I would expect from the product efficiencies. Do you figure that your gas stove was less than 40% efficient, or that something else is contributing to your energy savings? For example, I'd believe that a higher heat input reduces the time pot is on the stove, and hence the convective losses from the pot.

[Marc Rosenbaum]

Daniel -
I think the disproportionate savings are due to the energy used is the ramp up to the end point desired (usually, boiling). Once the water is boiling, the heat transfer efficiency ratio of roughly 2:1 is probably valid, but if it takes three times as long to get to the end point then the losses off the pot have got to be more.

[Seth Downs]

Thanks Marc for enlightening me about induction cooking (and Marathon hot water heaters, Fujitsu ductless minisplits, The Thousand Home challenge...). We are now the happy cookers over a Frigidaire induction stove and our one year old says thank you for not poising his air. By any chance do you have a recommendation for a whole house fan? I'm thinking that would be just the thing for the high dessert (Albuquerque) summer with cool nights.

[Kim Quirk]

Hi Marc,
I am also a very happy induction cooktop owner (Whirlpool). I went cold turkey -- all burners are induction. I had some pots and pans that work and I had to buy a few. I had a standard thermal electric cooktop before this and I love the low simmer and the very fast heat. According to the literature, it should save around 20% in electricity over the old one. I'm measuring all my electric use but I can't easily do a one-to-one comparison.

Has anyone else been able to cook the same thing on standard electric burners and on induction and then been able to measure the actual electricity used?

[Marc Rosenbaum]

Seth, no specific whole house fan recommendation. Usually belt driven ones have been quieter.
Kim, I don't know the extent of the data that's been taken on electric vs induction energy usage beyond the older report I read some time back.

[michelle]

What are folk using to cook in power outages which is normal at our location several days up to a week? Generator to run the induction or electric stove? Thnks Michelle

[Marc Rosenbaum]

Great question, Michelle. I've had a one burner propane stove and a 20 pound propane cylinder for years for just that type of event. For safety, the tank should remain outdoors, so i should run a permanent gas line from outdoors to inside to hook it up to (I had that in my NH house).