Overcooked myths: microwave ovens and home energy use

The Microwave Oven - hot stuffThe roving finger of home energy blame finds another target in today’s New York Times. The microwave oven is portrayed as the biggest guzzler of home energy in a confusing table of bar charts and percentages.

It’s true that newer technologies with always-on or standby functions are increasing the demand for home electricity, but we must remember that these aren’t all simply adding to the demand — sometimes they’re replacing it. The microwave is a perfect example.

For small meals, the microwave is by far and away the most efficient (and by extension eco-friendliest, and cheapest) way of cooking. In fact, the same meal can consume less than 1/5th (pdf) the amount of electricty if cooked in a microwave rather than a conventional convection oven.

So why the confusion? Well, it’s true that the microwave does have a very high energy consumption rate of around 800 watts. But nobody has the microwave oven on all day. This is where the numbers can get misleading — power ratings (generally given in watts) must be multiplied by the time the device is actually in use to make for simple comparisons. A little bit of math reveals that the microwave’s quick heating ability results in a net gain in efficiency over conventional stoves (if not necessarily a gain in good flavor).

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  1. DWD - August 9, 2006

    In a home that is “off the grid” the three biggest energy “hogs” are the microwave, hair dryer, and clothes dryer. Now, this is assuming propane appliances (clothes dryer, stove/oven, heat). The wattage used by these appliances require more than solar panels to operate (even considering storage capacity) and therefore require a generator of some sort. I can watch television and DVDs all day for the energy consumption of a microwave meal.

  2. Anonymous - August 9, 2006

    Have you read about what happens to the food value of your meal after cooking it in the microwave? In one old study (sorry I don’t remember the details) they tested broccoli before and after, and after microwave cooking it was not recognizable as food. I would rather have a cold meal, thanks! Are there any numbers on the energy consumption of toaster ovens and the like?

  3. pradwastes - August 10, 2006

    A 900 Watt microwave acually uses 1.5 kw while it is on. The microwate is not best thing for cooking anything as the manufacturer would like us to believe. In my kitchen, all the plug moldings are on the same breaker. Using a coffee maker, toaster and microwave will thow a 25 amp breaker if the rifigerator cyles on at the same time. Being on the grid is no help here.

    Microwaves are mostly used for reheating dinner and thawing out something frozen. In these rolls, the microwave works well. Microwave popcorn is better than any other way of preperation and it takes only a couple of minutes.

    It is not a fair comparison to compare it to the chothes dryer or oven because it normally is used for very short periods of time. The microwave heats water and fats directly and it is very efficent for heaing only the food.
    I will admit a potato tasts different when cooked in a microwave.

  4. Anne - August 10, 2006

    Microwaves can leak and they destroy the nutritional value of the food that is nuked. I get as far away as I can from them when they are being used. I have heard that it can effect well beyond the homeowner’s microwave.
    They can especially poison meat. When they first hit the market, I went to a presentation that suggested that microwaving food creates radiolytic damage to the isotopes in the food.

  5. Dave - August 11, 2006

    Are you serious? “Radiolytic??” Get off the conspiracy theory websites. They are poisoning your brain.

  6. simon - August 17, 2006

    The point is about energy transfer. Most of the energy that a microwave uses heats up the water in the food. Very little of it goes to heat up the oven and the room beyond, unlike convenitonal ovens eg fan ovens. Microwaves are not great for everything, but if you want food heating you can probably do a lot worse.
    I’m not sure about the argument that microwaves destroy nutrion in food. I cooked using only a microwave for two years (raw food not processed, TV dinners) and did not get scurvy.

  7. organic brian - August 18, 2006

    Dave, see below for a definition of the word “radiolytic” from the Merriam-Webster online dictionary, and a link to some info about liver cancer and radiolysis of irradiated foods. Why make fun of somebody else’s statements just because you’re uninformed?
    Main Entry: ra·di·ol·y·sis
    Pronunciation: “rA-dE-‘ä-l&-s&s
    Function: noun
    Etymology: New Latin
    : chemical decomposition by the action of radiation
    – ra·dio·lyt·ic /-dE-&-‘li-tik/ adjective

  8. Anonymous - October 12, 2006

    Most people who fear radiation are simply ignorant of it.
    Microwaves cook through friction. The so-called radiolytic compounds are also present in barbequed food.

  9. Daniel - December 4, 2006


    Electrical Engineer weighing in on a few comments:

    The original article mentioned that Microwave ovens consume less energy per meal cooked, than other means. This is by and large true, because microwaves don’t need to run as long as an electric burner or a gas flame to accomplish the same results.

    Where the train went off the rails for one respondent is the failure to understand the difference between power and energy. They are NOT the same. Energy is work- it can be a specific amount of heat, for example- a log contains a finite amount of energy, which is released as it burns. Power, on the other hand, is a measure of the RATE of energy usage (or generation).

    To use the log metaphor- If you have 2 identical logs, they should theoretically contain the same amount of energy. (a perfectly valid assumption). Now, burn one log with the damper half-open, and the other one full-throttle. The latter situation gives you a hotter flame, but the log burns out much faster. The wide-open stove is burning energy at a much higher rate, therefore, it carries a more powerful flame. At the end of the day, however, both stoves release the same amount of energy.

    The same is true of Electricity. Electrical energy is commonly measured in Kilowatt-Hours. One kilowatt-hour of electricity is the amount consumed by burning ten 100-watt lightbulbs for exactly one hour. You will be charged the going rate by your electric utility for this. If you turn off half of the lightbulbs, you use half as much energy, because the lightbulbs are burning with half the power for the same amount of time. You can also burn all ten for 30 minutes, and pay the same.

    Microwave ovens are very powerful devices. They gobble up the electricity far faster than many other cooking appliances, so your source of electricity, be it grid or PVA,’s etc, must be capable of delivering energy at a rapid enough rate for them to work at all. The upshot is, however, they run for a very short period of time, so the net energy savings is positive by comparison. Off-grid systems, however, are very limited as to how fast they can deliver the goods, so hungry devices like microwaves often cannot co-exist peacefully with the other electrical devices in the household.

    Now as far as “Radiolytic by-products,” or god forbid, “Isotopes” in the food…

    To put it inelegantly… that is B.S.

    One more time…and please listen carefully, OK people?

    P-U-R-E B-u-l-l S-*-*-t.

    Lemme explain why-

    In order for radiation to cause chemical changes to matter, it must be of a high enough energy to dislodge electrons from the orbits of atoms, or to dislodge a neutron from an atomic nucleus. (The latter is how isotopes are made). The name of such high-energy radiation is called “Ionizing Radiation.” For example, the least energetic of these are Ultraviolet wavelengths, on up to X-Rays, and gamma rays (which are released during the decay of some radioactive elements). Those are the bad guys. They will hurt you- very badly! By the way, all of them are ABOVE the spectrum of visible light, further and further increasing in energy. Energy goes as increasing frequency.

    But wait… I hear you cry… Microwaves make RAY-DEE-AY-SHUN, right (cue up scary theremin music).

    Yes, of course they do. So does a light bulb. So does your iron, so does your wireless telephone, so does your 100% certified-organic cow-chip space heater.

    Without going into a quantum physics or a Radiochemistry lecture, let me simply say that there are many, many, many different kinds of electromagnetic radiation in the universe, and forgive my sarcastic tone, but it drives me to distraction to hear people continually repeating the same old meme:

    RADIATION = BAD!!!!!!

    while being completely ignorant of the immutable laws of physics.

    MICROWAVES ARE NOT IONIZING RADIATION!!! The entire Microwave spectrum is FAR BELOW visible light wavelengths, and as far as ionizing danger goes, your ligtbulb is more dangerous.


    (Simple chemical reactions that occur by the simple application of heat are another matter, but you don’t even need a microwave oven for those!)

    If anyone wants to go up against the pantheon of quantum physicists from Madam Curie’s time to the present day, be my guest. I’ll leave that as an exercise to the student.

    Microwave ovens, if used inartfully, tend to cook the ^%$#@! out of certain foods, rendering them, for the most part, inedible. But they will not result in food that is any more hazardous to health than if cooked-to-death by any other means, with the possible execptions of exposure to Cobalt-60, or a thermonuclear bomb.

    I am sorry I had to post such a lengthy polemic, but this really bugs me. For the record, I have unimpeachable liberal/progressive/ecological bona-fides, and I walk upon Mother Earth with as light of a footprint as possible. However, I am also a trained engineer and scientist, and I can’t tell you how many times I have cringed to hear the ignorant spoutings of otherwise well-intentioned people trying to make their cases- some of them valid, some of them simply snake-oil salesmen who are just out to sell books, seminars and worthless supplements to an ignorant and under-educated public. Just look at the “alternative” vanity publishers these people use. Nobody legit will even touch them!

    Finally- people- please, if you are fighting for a progressive cause, you have my 100% support. But please, do your homework. Learn your science, and don’t be afraid to call BULL-SH*T on the charlatans in your midst (and there are a LOT of them!).

    The Elephant in the Room is that far too many so-called alternatistas are guilty of the same kind of faulty reasoning, illogic and idol-worship of Christian and Islamic fundamentalists. Beware false-prophets. Scientific theories are testable, and as such, know no ideology, so beware false prophets and intellectual LA-ZI-NESS!

    If you think my vitriol is bad, just imagine what a REAL enemy of your cause will do as he gleefully, and justifiably, pokes huge gaping holes through all of the Junk Science that is out there, and repeated ad-nauseum with no critical thinking, whatsoever.

    I’m on YOUR side, don’t forget.

    Thanks for listening.

    Peace to all, and do be well.


  10. Angela - December 4, 2006


    Thanks for the awesome comment. A very well-reasoned treatise that actually provides more insight than the original post. 😉

    For the record, the link on ‘radiolytic’ compounds is related to the irradiation of food in order to kill things like salmonella – not really in support of the ‘microwave is evil!’ discussion.

    Thanks for the info Daniel.

  11. Dan - December 8, 2006

    Someone above mentioned microwaves are a good way to cook popcorn. They might be from an energy standpoint, I don’t know, but there seems to be increasing evidence those non-stick bags are less than healthy…Worth using the stove for?



  12. Maria - August 13, 2007

    Microwaves do not destroy nutrients. This is misinformation. I went to a chiropractor at one time for back pain who tried to convince me of the evils of microwaving food and other utter nonsense.
    An excerpt: “In studies at Cornell University, scientists looked at the effects of cooking on water-soluble vitamins in vegetables and found that spinach retained nearly all its folate when cooked in a microwave, but lost about 77 percent when cooked on a stove. They also found that bacon cooked by microwave has significantly lower levels of cancer-causing nitrosamines than conventionally cooked bacon.
    When it comes to vegetables, adding water can greatly accelerate the loss of nutrients. One study published in the Journal of the Science of Food and Agriculture in 2003 found that broccoli cooked by microwave — and immersed in water — loses about 74 percent to 97 percent of its antioxidants. When steamed or cooked without water, the broccoli retained most of its nutrients.”
    I would believe the guys at Cornell University before I would believe quacks like “Drs.” Mercola and Weil.

  13. Robin - December 26, 2007

    you can cook popcorn in the microwave in plain old paper bags…it’s cheaper, too. here’s a link to the basic recipe.

  14. Rapids$!t - July 16, 2008

    Regarding the comment about the study that microwaved broccoli lost it’s nutrition, it’s because they boiled the broccoli in lots of water in the microwave and most nutrients simply ended up in the water. If you heat the broccoli by itself or steam it, no more nutrient loss occurs than if you used a stove. In the end, microwaves cook by heating–it’s just that it’s a direct method of heating, without an intermediate (flame, hot surface of pan, hot air, hot water, etc.)