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How to boil water - Gas stove or Microwave

sueinphillysueinphilly Posts: 4,207Registered User Senior Member
edited November 2009 in Parent Cafe
Assume I want to bring 1 cup of tap water up to barely a boil.

I have an 1100 Watt microwave or a gas stove.

Which costs less to use to produce desired effect?

I don't care if one takes longer than the other
Post edited by sueinphilly on
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Replies to: How to boil water - Gas stove or Microwave

  • mominvamominva Posts: 2,276Registered User Senior Member
    Don't know about cost. Stove is safer. (I remember the stories about burn injuries from the eruption of hot microwaved liquids when the surface tension is broken.)
  • mafoolmafool Posts: 6,453Registered User Senior Member
    This will depend, in part, on the relative costs of electricity and gas in your area.

    On a stove, you need to heat the pan in order to heat the water, and there is waste heat. In a microwave, you heat the water, and some of that heat is "wasted" in heating up the container and the surrounding air.

    Wild guess coming: I think you use less energy in the microwave.

    Any physicists in the house?
  • bomgeedadbomgeedad Posts: 350Registered User Junior Member
    I always wonder about this question for a electric stove because that is what I got.

    Just for the energy to heat up the water, I am sure that a microwave use more energy. However, with a stove you also heating the pot. I never pour a cup of water into the pot that means I usually heat more than a cup of water. When water boils, the stove is still hot, that means energy is being wasted.

    So it is interesting to see whether microwave or stove wins.

    After posting I see mafool's post which also cover the same point about heat is wasted on the pan/pot.

    Microwave works by heating water molecule, not much heat is wasted in heating the container(cup) and air.
  • mafoolmafool Posts: 6,453Registered User Senior Member
    leave it to an engineering student.

    I asked my son, and now he is discussing the fact that energy is lost in converting coal into electricity, so we can't really compare the energy used in the two methods.....

    So. My answer is, forget boiling water for tea and have some wine, instead. Then you won't care!
  • swimcatsmomswimcatsmom Posts: 14,998Registered User Senior Member
    My answer is, forget boiling water for tea and have some wine, instead.
    Funny :D

    But for breakfast (for those like me that would be unconcious for the rest of the day after wine for breakfast) how about an electric kettle. I am English so lots of cups of tea - I use an electric kettle. They are easier to find than when I first moved here. Don't know how many cents it costs to boil the water - I am hazarding a guess it is cheaper than in a pan because the element is just heating the water not the pan. Definitely quicker.
  • oregonianmomoregonianmom Posts: 1,983Registered User Senior Member
    Every week I bring one cup of water to boil in a pyrex measuring cup - in the microwave. Takes 3 minutes. Then I stir in 1/4 cup of sugar. Voila! - hummingbird nectar!

    I used to do it on the stove, but it took longer and then I had a pot to clean. The pyrex cup just goes into the dishwasher. :D
  • mafoolmafool Posts: 6,453Registered User Senior Member
    ^^^I should have include a disclaimer for Brits! ;)
  • sueinphillysueinphilly Posts: 4,207Registered User Senior Member
    Wine will be funny with my oatmeal.....

    I just got a new microwave (1984 model finally died). The old one was 650 watts and the new one is 1100 watts.

    It is really really fast at its highest power setting.

    FWIW, looking at my latest electric bill, my net cost per Kwh is .212 (that is taking the avg usage/billed $)

    So if I use the microwave at full power for 1 minute, it costs ?

    Where is the electrical engineer when you need one.
  • yayverilyyayverily Posts: 222Registered User Junior Member
    Sheesh. This is like taking the SAT.

    1100W microwave operating for 2 minutes (that's all it should take) will consume 0.0367 kW-hrs of electricity. My electricity costs $0.146/kW-hr, so it would cost $0.0054 for each cup of water boiled in the microwave.

    It would be difficult to figure out how much gas you use to boil a cup of water on the stovetop (unless you have a flowmeter on your gas line), but I'm going to say the microwave is probably cheaper, primarily because it's putting the energy only where it's needed--into the water. A lot of wasted energy/heat goes into boiling water in a pot on a stovetop.

    Now, what if you start with hot water from your tap? You would need less additional energy to make it boil than if were cold to start with. You could save a few tenths of a cent for every cup of water boiled...money in the bank!

    This discussion reminds me of the time Kramer decided to return the soda cans and bottles to Michigan for a higher refund.
    The Bottle Deposit, Part 1 - Wikipedia, the free encyclopedia
  • bomgeedadbomgeedad Posts: 350Registered User Junior Member
    1100W is the output power, the actual power usage is higher and depends on the model, it should be given on the spec of the microwave. Wiki claims the typical efficiency is about 64%.

    One interesting fact I read is that some guy measure microwave usage using one of those kill-a-watt device and finds the microwave clock uses as much electricity as 7 minute of full power microwave.
  • rocketman08rocketman08 Posts: 1,194Registered User Member
    It's actually quite dangerous to boil water on it's own in a microwave. If you simply place water in a smooth glass container and 'boil' it in there you can actually superheat the water beyond it's boiling point due to a lack of nucleation sites. If the glass is then bumped (when trying to pick it up) or something with lots of nucleation sites added (e.g. some freeze dried coffee) the water will then errupt violently and it's easy to get seriously burned.

    As for the original question there are a number of factors to consider (e.g. how was the electricity originally generated) but in general I'd say the gas burner is much more efficient. Some power plants use natural gas or other fossil fuels (e.g. coal) to generate electricity. During that process you have to boil water to make steam to turn a tubine to make electricity. That electricity is then sent to your house (with a lot lost on thew way) and then finally used to generate microwaves (which isn't 100% efficient) used to finally boil water again. Therefore it would take much less energy to simply boil the water with a fossil fuel right at the beginning than using a fossil fuel to boil water for making electricity to only then use that electricity to boil water again.

    So the gas burner would be the 'greener' option (if the electric was made with fossil fuels... which most is). I imagine it would be cheaper too, but I don't have the figures.
  • sueinphillysueinphilly Posts: 4,207Registered User Senior Member
    1.60Kw as power usage (does that make sense).

    About the clock using more power than the microwave. I had to google that. I will now be pulling the plug when not in use. I'd do that for vcrs and tvs too, but then all the settings get reset every time.

    Hidden Energy Bandits: Things that use electricity even when they're off

    The clock on the microwave uses more energy than the oven

    The first time I heard that statement I thought,"Great, another electrical myth, like the myth that you should leave lights on because they take a lot of electricity to start up.". After all, I knew that the oven uses about 1000 watts while the clock uses five.

    But then I thought, wait a minute, the clock is running 24/7, while the oven is running just a few minutes a day. Then I did the math:

    How much energy the clock uses in a day: 5 (watts) x 24 (hours) = 120 (watt-hours)

    How long it takes the microwave to the same amount of energy:
    120 watt-hours / 1000 watts = 0.12 hours, or 7.2 minutes

    This means that if you use a typical microwave oven for less than 7.2 minutes/day, the clock uses more electricity than the oven. Wow.
  • Barneyfife2008Barneyfife2008 Posts: 135- New Member
    I was told to throw a toothpick into water for the microwave as it superheats without something to "hold onto".
  • yayverilyyayverily Posts: 222Registered User Junior Member
    OP wanted to know which is lower cost--microwave or stove top.

    1.6kW power consumption microwave running for 2 minutes uses 0.0533 kW-hr. At $0.212/kW-hr (her cost), that is a cost of $0.0113 to boil a cup of water. That's the easy one. Microwave is very efficient when it comes to putting the heat into the water and not the room, but as others have pointed out the efficiency of generating the electricity in the first place factors in (about 60% efficiency is typical for power plants burning natural gas).

    Going rate for natural gas is about $1.58/therm, where a therm is 100,000 BTUs. It takes 1BTU to raise temp of 1lb of water by 1 degree F. If all the heat went into the water (it doesn't), then it would take 73 BTUs to raise the temp of 1 cup of water (0.52 lbs) by 140 degrees (from 72 to 212). Cost of this is only $.0012, or 10 times lower than for the microwave. In reality, on the stovetop, much of the heat is lost--found one example on-line of someone boiling a quart of water in 6 min on an 18K BTU/hr gas burner. That works out to $0.0284 (about 3 cents) to heat up the quart, or $0.0071 for each cup, and says only about 17% of the heat generated by burning the gas is actually going into heating the water--so the efficiency of using the gas stove to heat up water is actually pretty low, but the cost to boil a cup of water may still be a tad lower than using the microwave (and that is true only if you use a small pot and heat up only one cup of water, not a larger amount).

    A third method of boiling water seems to be favored in the UK--the "plastic electric jug-kettle", which uses a fully immersed heating element and couples the heat from the filament into the water much more effectively than a stove top. This still uses electricity, but is far more efficient (close to 100%?) than the microwave (which, as noted by bomgeedad, is about 64% efficient at converting 110V AC to microwave energy). This is the cheapest way to boil a cup of water, and the "ECO-kettle" is advertised as good for the environment as well (since it heats up only the amount of water that you need, and does so efficiently).
    Eco Worrier - Times Online - WBLG: Kettle versus hob debate
    Eco Kettle - save energy with The Eco Kettle
  • sueinphillysueinphilly Posts: 4,207Registered User Senior Member
    thank you very much for your very thorough analysis.

    The idea of putting a heating element into the water just seems weird to me.

    I'll probably use the microwave because it only takes about 90 seconds to get the water to the temp I need (or to reheat a cup of coffee)
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