Updated on 07.31.14

Saving Pennies or Dollars? Hot Water or the Microwave

Trent Hamm

saving pennies or dollarsSaving Pennies or Dollars is a new semi-regular series on The Simple Dollar, inspired by a great discussion on The Simple Dollar’s Facebook page concerning frugal tactics that might not really save that much money. I’m going to take some of the scenarios described by the readers there and try to break down the numbers to see if the savings is really worth the time invested.

Jessie said, Here is a practice that my mother does when the extended family is over for the weekend and I wonder if you can do the calculations for us:

Option one: keeping a hot water urn plugged in from 9pm-11am.
Option two: zapping a mug filled with water in the microwave for 2 minutes.

My mother estimates that it costs more to keep the urn plugged in for that time than for the 6 times the microwave would be used for 2 minutes each. Bear in mind that a few more people would probably drink the hot water if it was in the urn. Without the urn, only the people who really want coffee or tea will make themselves a cup.

The solution here, of course, is to calculate the cost of each method.

Calculating cost of microwave use A typical microwave oven uses 1,500 watts, or 1.5 kilowatts, of power. If you’re microwaving water for two minutes and repeating this six times, you’re using the microwave for twelve minutes, or 0.2 hours. This means that the microwave, in this usage situation, would consume 0.3 kWh (1.5 kilowatts times 0.2 hours) of energy. At the usual national rate of $0.11 per kilowatt hour, the cost of the microwave usage is about $0.03.

Calculating cost of the urn The only clear estimate I could find for the energy consumption of a typical hot water urn was approximately 180 watts in standby mode and 1,000 watts while heating. Looking at additional information about urns, I’ve found that they typically heat the water to boiling in about fifteen minutes. Thus, during the heating portion of the equation, the urn consumes 0.25 kWh (1 kilowatt of energy consumed over 0.25 hours) and during the 14 hours of standby, the urn consumes 2.52 kWh (0.18 kilowatts of energy consumed over 14 hours). At a typical household rate of $0.11 per kilowatt hour, the cost of heating the water and keeping the water near boiling in the urn overnight and in the morning is about $0.31.

Clearly, in the situation you describe, the microwave wins out. It costs less than using the microwave than it does to simply heat up the water in a typical urn, let alone keeping the water warm for any period of time.

Naturally, this difference can be easily mitigated with some changes. Let’s say, for example, that you just have the first person to wake plug in the urn. This would reduce the standby period to, say, five hours. This would consume a total of 1.15 kWh, which would add up to only $0.13 (approximately).

It’s also worth considering the convenience of using the urn. As you’ve mentioned, the convenience of urn use convinces people to use it versus microwaving water. If all they have to do is flip a switch to get very hot water, it’s much easier than filling up the cup and using the microwave.

The question really is how much that convenience is really worth for you or your mother-in-law. If the value of having that reservoir of hot water is worth another quarter of electricity, then she should keep using it.

Clearly the microwave is the less expensive option, but this falls into saving pennies rather than saving dollars.

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  1. Beth says:

    Why not just use an electric kettle? That’ll give you evenly heated water (which is a concern especially with microwaving water for proper tea). My kettle’s power usage is about 2kWh and that translates to maybe 30 seconds to boil a cup of water.

  2. moom says:

    Electric kettles are not common in the US. I had to buy one online when I lived there.

  3. lurker carl says:

    Most people I know run the faucet until the water gets hot to reduce their time waiting for their water to boil. A point-of-use instant hot water dispenser may be a better option.

  4. Jules says:

    I wonder why electric kettles aren’t more popular in the US. We got one soon after I moved to the Netherlands, and I cannot imagine life without it. The one disadvantage of the thing is that it’s noisy, but at least you don’t forget about it.

  5. valleycat1 says:

    We use an electric kettle here in the US. Once I heat the water in the morning, I don’t have to re-heat for the second cup of tea. So I’m with Beth.

    One added advantage Mom’s use of the urn over the microwave is that you don’t have to listen to all the door slamming & bell dinging every time someone heats up a cup. For me, that’s well worth a quarter a weekend.

  6. Tanya says:

    I was about to suggest electric kettles, as well. We have a couple that heat water quickly, and shut themselves off when the water’s hot.

    And you don’t get that “cup handle is hotter than the water inside” situation that occurs when you heat water in the microwave.

  7. Tracy says:

    I use an electric kettle as well – it’s quick, easy and it gets the water to the right temperature (neither a hot water urn or the microwave really do that.)

    You can pick one up for about 10 dollars.

  8. Baley says:

    I agree with the electric kettle idea. They are available in the U.S. (try a Bed, Bath, and Beyond-type store), and they are super efficient at heating water (at least time-wise; not sure about cost), and you can boil several cups at once. They’re great!

  9. Vanessa says:

    I bought an electric kettle as a wedding gift for a coworker just a few months ago. And yep, I got it from Bed, Bath and Beyond.

    I remember an episode of Good Eats years ago where Alton was using an electric kettle (for coffee?) so while not popular, they have been available for quite awhile.

  10. Nick says:

    This is kind of ridiculous.

    Just use whatever option is most convenient for you.

    There has to be a better way to spend your time than worrying about the pennies your saving on something trivial like this.

  11. Luke G. says:

    To clarify my earlier comment about not using hot water…I meant it in regards to using hot TAP water. I just realized that my comment was a bit ambiguous.

    Sorry! :)

  12. valleycat1 says:

    #10 Nick +1

    All of these saving pennies posts have been pretty useless. And if you go back & realize you’re doing some & not the others, it all balances out.

    For example, I have been a loyal brand-name gasoline buyer forever, much to my spouse’s chagrin. But I figure the extra 10 cents/gallon pays for itself because I have tracked & really do get better mileage with the better gasoline. [No need for anyone to explain to me it may all come out of the same tanker truck.]

    The only way to really save money is to tackle the big stuff and costly bad habits. This nit picking is just a diversionary tactic IMO.

  13. jim says:

    I also vote for an electric kettle. We have one and its great. My guess is that they aren’t as common in the US because we don’t drink as much tea here nor use coffee presses much. America store shelves have 25 coffee makers and maybe 2 tea pots.

    To those who think saving pennies is useless then please note that 31¢ vs 3¢ is 28¢ per day which adds up to $102 for a full year. $102 in a year is not trivial especially if you find a few things like this. Yes obviously bigger financial issues have more impact but that doesn’t mean that wasting $100 a year is a good idea now does it??

  14. Amy says:

    I think most people who frequently read personal finance blogs are on top of the big things. The only way to continue to save is to look at the small things. And as Jim pointed out, the small things DO add up over time.

    On another note, is an electric kettle the same thing as a hot pot?

  15. Kim says:

    I just cannot help but to think of the safety factor of leaving something heating up over night, especially when everyone is sleeping. Is this an item that’s been around for years? What’s the likelihood that it’ll catch on fire? To me, I like the microwave for that reason. If something does happen, you’re right there watching it and can deal with the situation.

    For what it’s worth… I’m also not the type to use a crockpot unless I’ll be home all day.

  16. AndreaS says:

    I happen to like these pennies-or-dollars posts. Many of Trent’s posts on time management, goal setting and so on, tend to blend for me. I like the specificity of these posts.

    Each of us does hundreds of little actions every day that impact our resources. It is interesting to one time make the effort to figure out which is the cheapest way, then make it a habit to do it the cheap way. For example, there are two routes I can take to the major city near me. It’s worth it to measure the mileage, and then forever on drive the shorter of the two routes. I figure each action out one time then never think about it again.
    As previous posters said, the cumulative impact of these small changes, over time, can add up to significant money over the course of a year.

  17. Evita says:

    I agree with Nick and Valleycat…….. those penny-pinching posts are not worth the time Trent spents writing them……… and my time reading them!
    For the record, I just boil the water on the gas stove (probably awfully wasteful but whatever….)

  18. LaDonna says:

    Another option is to heat a kettle full of water and pour it in a big Thermos. It’ll stay hot enough for tea for most of the day.

  19. lurker carl says:

    #16 AndreaS – The shortest route is often neither the cheapest or fastest, YMMV.

  20. krantcents says:

    Sometimes it isn’t worth chasing pennies unless it s every day. Some occasional savings of pennies can be meaningful, but it has to be continuous.

  21. BJD says:

    I fully agree with those saying this series is something that can be dropped.

    To #13 Jim – your point would be more valuable if it was an everyday expense but the writer clearly states “Here is a practice that my mother does when the extended family is over for the weekend” so you probably at best looking at a 12 to 24 days during a year; cost savings probably much less than $5 per year.

  22. valleycat1 says:

    I would disagree that most of Trent’s readers have a handle on the big stuff – just look at the questions he answers every week. For most people pennies saved disappear. I doubt that if they take this advice, for example, & even save $1 a month on electric, that that $1 makes any impact in their quality of life or ability to pay bills.

    Another example – I have friends who make an effort to buy sodas for home consumption only on sale (or not buying them at all), but then thinking nothing of getting one every day for lunch at the fast food counter for over a dollar each.

  23. Andrew says:

    I like these posts, even the ones that point miniscule savings because it demonstrates that extra effort vs. convenience is not always a deal that provides an financial return. It’s not nit-picking for pennies to put in the piggy bank – it’s a demonstration that not every supposed money saving habit has a measurable return.

  24. ChrisD says:

    I liked this post, but more because it shows that something is NOT worth bothering with than because it is. I was very surprised that leaving an urn on for 14 hours only costs 30c in electricity, I would have thought it would be a lot more. I might have though it was equivalent to microwaving 30 cups instead of only 10.

    For a few cups an electric kettle is ideal, esp as you can switch it on the boil and forget about it as it switches itself off. BUT you do need to top up the water if you want more than ~8 cups so if there is not a sink in the room…
    Combining the urn with a timer switch would save it from being on all night. I suppose saving electricity for the environment is still worth doing.

  25. Angie says:

    I like the posts, too. And they ARE called “Saving Pennies or Dollars”, so it’s not like he’s trying to waste your time or hoodwink you.

    Here’s a thought if you don’t care for them: don’t read em!

  26. John says:

    Why not put the urn on a timer to start 15 minutes before the first person is to use it??

  27. tall bill says:

    Hey Trent;

    Urns, much like a coffe pot, have internal thermostats which cycle on 100% to bring the water up to temp, then, based on ambient temperature, cycle say 20 – 60% to hold temp & not let it boil over. Your math assumed 100% which is not the case. Regardless, let’s assume 50% over several hours which would still be around $0.15 – still much higher than a microwave.

    We to have gone to an electric kettle which comes up to a boil in 2-3 mins & shuts itself off, staying hot enough for about an hour allowing the family to mix their drinks, etc for for the morning. Probably on par with the microwave or a penny or two more.

  28. Maggie says:

    I really like the posts. There are lots of sites to find out about spending and saving large dollars but not many on saving pennies. Once I read Trent’s article, it is then my choice whether to use his tips or not. I have found that a few cents here and there make a difference over time. I save all my change and a penny here and there do add up. I purchased a recliner for my husband with my change a few years ago. So $0.25 does make a difference. Keep these coming, Trent.

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