On boiling water for tea

26 Feb 2007

Got questions about the environment? Ask Umbra.

Dear Umbra,

My roommates seem to be constantly boiling water for tea. We've got a gas stove, a microwave, and an electric teakettle. However, we don't know which option is most efficient. Any ideas?

Kate R.
Syracuse, N.Y.

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Dearest Kate,

Idears-R-Me, and microwaved tea is nasty. Nas-tea, I suppose I must say, if I wish my membership in the Cheap Joke Association to be renewed.

To nuke or not to nuke?

Photo: iStockphoto

To recast your question in another way: which of these appliances spends the most energy heating the water and the least energy heating itself, the air, or any other involved items? A review of the literature (various governmental energy-efficiency advisories, like this one from Canada) indicates that the electric kettle is No. 1 in efficiency. Let's use logic to arrive at the same conclusion.

First examine the gas range as it heats a vessel filled with water. Note the open flame, which may or may not fit underneath the vessel. The flame is merrily heating the vessel, which must be well heated before the water can begin to warm. The flame is also -- it cannot avoid -- heating the nearby air. How much of the gas heat is lost around the edges of the vessel will of course depend on the size of the vessel, the size of the flame, and the operator of the stove.

You may be interested to learn that microwave oven digital displays are responsible for the lion's share of their power draw -- 80 percent, by one reckoning. (This means unplugging microwaves when they're not in use is a good way to increase their efficiency and decrease your overall energy use. Ditto for other home appliances and electronics.) In terms of efficiency, the microwaves inside the oven work their magic and heat only the targeted object, not the enclosed air, nor is any of the microwaves' embodied energy lost as a byproduct of combustion. There is no combustion. The waves (micro, as established) hit the water and the cup itself, causing their molecules to bounce about, rub against one another, and become hottish. Microwaves are very efficient at heating food, but in my opinion, microwaved water doesn't hold heat long enough to make decent tea. And overheating water in a microwave in an effort to get it sufficiently hot is dangerous. If your roommates prefer weak tea in tepid water, however, who am I to interfere? Bleagh.

The electric kettle has a heating element in direct contact with the water. If the kettle itself is an efficient model, little heat will be lost to the vessel or the surrounding air. When the water has been heated (hopefully boiled), the same efficient kettle should automatically shut off. Alright, I said logic, but logic does not tell us why a microwave is less efficient than a kettle at heating water, unless my snooty opinion about poor water heating in a microwave is actually germane. I've been looking for widely accepted efficiency percentiles on these three items to no avail. An efficiency percentile would tell us how much of the energy spent actually went to heating the water -- you can find this type of number for a home water heater, for example.

All I can tell you, in conclusion, is that the government energy-efficiency advisories prefer the kettle over other means. Let's trust they've done the analysis, and are not all just copying each other and creating one giant chain of misinformation. Fortunately this is a very small matter compared to issues such as personal vehicle emissions, and we can trust that going with the kettle is probably not so bad.

Firmly,
Umbra

Yours is to wonder why, hers is to answer (or try). Please send Umbra any nagging question pertaining to the environment -- but first check out her FAQs!

The claims made in this column may not reflect the views of this magazine. Neither the magazine nor the author guarantees that any advice contained in this column is wise or safe. Please use this column at your own risk.

Umbra Fisk is Grist Research Associate II, Hardcover and Periodicals Unit, floors 2B-4B.

Comments: (23 comments)

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Home hot-hot water taps?

Hi, Umbra,

This article brought to mind those home hot-hot water taps, the kind that dispense 190-degree water on command. Does one sacrifice greeniness for convenience in that case?

Thanks!
Rebekkah

-- Rebekkah Hilgraves, soprano "To sing well is to pray twice." -St. Augustine

by rebekkahhilgraves at 10:51 AM on 26 Feb 2007

Hot Water

Umbra, I'm usually a fan of your well-informed responses, but your comment that, "in my opinion, microwaved water doesn't hold heat long enough to make decent tea" just doesn't hold water. The heat capacity of water is unrelated to the method used to heat it; water of a certain temperature doesn't "care" how it got there.

I challenge you to a blindfold taste test of tea made with water heated in the microwave vs. water heated in an electric kettle.

The microwave is clearly the most efficient method to heat water for any purpose. Not to mention that an electric kettle is an appliance that is only good for one purpose (heating water) while a microwave can serve many functions (heating anything) making it superior from the manufacturing and durable goods waste standpoint as well.

by river2sea72 at 10:51 AM on 26 Feb 2007

Heating Water

Did the comparison of an electric kettle to a gas range take into consideration the energy loss before the electric kettle heats the water? Since approximately two-thirds of the energy used to make electricity is lost to waste heat and other losses, the losses could be comparable to the gas heat losses you describe with a gas range.

by drosenblum at 11:13 AM on 26 Feb 2007

Microwave tested

I performed a scientific test. I have a "Kill-a-watt" watt-hour meter. I plugged the microwave into it and made 500ml of hot water, measuring the temperature before and after. I did the same with a electric kettle, stopping the kettle when it reached the same temperature as the microwaved water. Anyone can repeat this experiment with a $40 "Kill-a-watt" and a thermometer.

I don't have my notes handy, but the microwave was quite a bit more efficient in this simple case.

Another thing in the microwave's favor is that you make exactly as much hot water as you want. In the electric kettle, you either measure and pour, take a chance at not having a full cup, or heat extra water, which ends up getting dissipated.

In the kettle's favor is (as you point out) the "phantom load" of the microwave, which uses energy just to show you a flashing "12:00", since the instructions got thrown away long ago and no one can recall how to set the clock. I search for old, thrift-store microwaves with mechanical timers -- no light show, but no phantom load, either.

Also in the kettle's favor is what I would assume is a higher embodied energy in the microwave. On a mass-basis alone, the microwave consumed more energy in its manufacture. Considering the electronic parts and special materials pushes the embedded energy up even more. Then there's the greater disposal problem, too.

Let me know if you'd like me to dig out my notes for exact kilowatt-hour consumption of both devices.

:::: Jan Steinman, EcoReality. ::::

by Bytesmiths at 11:55 AM on 26 Feb 2007

Efficiency & Good Tea

In addition to looking at the heat loss and inefficiencies in the energy plant and in losses assoiciated with delivering electricity to your home, we should also consider the energy required to stimulate the heating elements in the electric teapot. I learned in installing a solar setup that household appliances with heating elements are some of the biggest energy hogs we own. (hairdryers, toasters, coffee makers, irons, curling irons, electric stoves, etc)

Another seasonal consideration is; if you are drinking tea in the winter and heating your house with natural gas. A little heat loss around your pot of boiling water is only lending a helping hand to your furnace.

Its a complex equation, but I'd be surprised if the electric teapot doesn't come out last on the list in terms of efficiency, and the microwave first.

PS- A Nast-tea tip. A problem with the electric kettle is that it automatically boils the water. This is fine for black and herbal teas, but if you like green tea, you should steep the leaves (use whole leaves, not tea crumbs) between 170-180 degrees F. Boiling the water or oversteeping makes it taste bitter.

by gavnoyes at 12:29 PM on 26 Feb 2007

Home hot water taps

Rebekka,

One of the first things I did when I moved into my current house is to unplug the 190 degree F hot water tap that was installed on my kitchen sink. Such devices are basically mini hot water heaters, sans any insulation, that keep a cup or two of water at a constant sub-boiling temperature. They consume enormous amounts of electricity. Even if you are home all day and consume frequent hot beverages, this is like keeping your electric kettle on simmer 24/7. IMHO, the convenience of having such instant hot water is not worth the impact on the planet.

Anyone who thinks they might consume more than one cup of hot beverage in a sitting might want to try making a bigger batch and using a thermos to keep the stuff warm. That or an old-fashioned tea cozy over the teapot. BTW I once won a "Queen Mum" lookalike contest wearing such a tea cozy as a hat!

by rivergal at 12:30 PM on 26 Feb 2007

kettle issues heating

Not to mention the landfill issues from disposing burnt-out electric kettles!

by hmester at 1:08 PM on 26 Feb 2007
[ Parent ]

Eco kettle

Hmm - just tried to post a minute ago but think I screwed it up...here goes again!

I have a smart new kettle that boils only the water you intend to use. It's really easy to use and if you're just boiling water for one or two cups of tea, it's super fast.

Check it out.

by naat at 2:01 PM on 26 Feb 2007

Spelling

I love "Ask Umbra." The English teacher in my soul wants to point out that in the US, all right is always spelled as two words. (It's often spelled as one word in the UK, in case you're wondering.)

by ballroom16 at 3:42 PM on 26 Feb 2007

It does seem to me that microwaved water...

loses its heat more quickly than water heated in a kettle or on a stove (and thus is not as good for steeping tea.) I don't know why this is but it's something I have observed for years. I think it is true of foods as well as liquids. I know this because, in addition to my observations in my own kitchen, I worked at a restaurant where foods that were microwaved were always being sent back to the kitchen because they weren't warm enough even if they were taken directly from the microwave to the customer, whereas the foods that came off the stove were never sent back for being thermatically challenged.

by Roz Cummins at 5:26 PM on 26 Feb 2007

put the kettle on, love

You're right, it's all a bit petty in the greater scheme of things, though as a Brit, tea takes on greater significance than is necessarily healthy.
Anyhow, to the point: studies I have done (as in, me asking my family and friends) suggest that electric kettles get popped back on with far greater frequency than kettles on the stove. People turn the electric kettle on, forget to make the cup of tea immediately, then turn it on again to re-boil the water. This would seem to negate the saving made by kettles, and takes me back to my first comment of the petty-ness of it all...

by mgrist at 7:17 PM on 26 Feb 2007

Making Tea

The most Green and best tasting way to make tea is with the SUN. One gallon glass jar (a fancy one with a spigot near the bottom if you must). Fill the jar with clean water, drop in the number of tea bags to suit your taste, screw on the lid, and set it in the sun. The darker it gets, the hotter it gets, the darker it gets....
The UV from the sun also kills bacteria.

JGMDakota

by JGMDakota at 12:52 AM on 27 Feb 2007

Microwave Leaking or Vampire Power Loss

Concerning, "You may be interested to learn that microwave oven digital displays are responsible for the lion's share of their power draw -- 80 percent, by one reckoning. (This means unplugging microwaves when they're not in use is a good way to increase their efficiency and decrease your overall energy use. Ditto for other home appliances and electronics.)"

My preference is to use a Microwave Oven with simple mechanical timer and no display (I can't figure out all those darn buttons and menus anyway). In stand-by, the non-display, non-electronic control type consume no power. There is less to fail and go wrong. I lived three years in Zaire,(Congo) Africa. The simple mechanical dial type Microwave was the only type that would survive the horrible power fluctuations.

JGMDakota

by JGMDakota at 1:34 AM on 27 Feb 2007

electric tea kettles made of plastic?

Does anyone know if the boiling of water in the plastic kettles leaches anything toxic into the water?

by myndwalk at 4:48 AM on 27 Feb 2007

tea kettles

Another vote here against the ickiness of microwaved tea water.

I have a Capresso electric tea kettle, heats up very fast, turns off automatically, with a glass pot. A bit pricey, but worth it.

by peapack at 9:28 AM on 27 Feb 2007

hot water

In the winter, I keep my tea kettle on my wood-burning stove and the water is kept close to boiling by setting it a little off the side. In the summer, I make sun tea. The microwave does make for good backup.

by bailsout at 1:32 PM on 27 Feb 2007

Microwaves are Most Efficient

I remember reading that a Microwave will ALWAYS be the most efficient way to heat water.
That's because heating water is how a microwave cooks, or so I read.

Allegedly, the frequency a microwave operates at is the EXACT frequency to add energy to Water. Thus, the water gets hotter. Then, the hot water in the food radiates this heat out to the rest of it. This is why microwaves sometimes don't cook things as well as we'd like.

Also, an electric kettle, by its nature, would be less efficient. It uses electricity to heat a piece of metal, and then this metal radiates its heat to the water.
Plus, electric kettles are plastic, crappy plastic at that.
For the life of a microwave (also a multi-tasker), I would have to get several electric kettles. Plastics always reach a point where they're just too gross to keep using...Espescially those electric kettles...I'll never have one again....

by TheSSG at 2:18 PM on 27 Feb 2007

teapot crackpot

Dear Umbra,
I too disagree with your teapot assessment. I would argue that the gas stove is by far the best way to make your tea. The Canadian report you cited did not mention gas, only electric range tops. My 1000 BTU gas stove boils 2 cups of water in 3.75 minutes. Given the heat capacity of water, this means (following a few calculations) that my gas burner is rouglhly 30% to 40% efficient at raising the temperature of water. Power plants are about 30% efficient in generating and transmitting electricity (~33% efficient in generation and ~93% efficient in transmission). If your electric kettle were 100% efficient, it still would not beat my gas stove. In addition, 50% of the electricity in the US is generated by burning coal, with far-reaching environmental consequences compared to the relatively clean-burning gas in my stove. Finally, regarding microwaved tea water. It might taste the same as stove-top water, but tea is supposed to be savored slowly, not microwaved.

by davidshull at 2:22 PM on 27 Feb 2007

Sun Tea In Microwaved Temperatures

Most UV passing through glass is converted to IR radiation, so don't count on Mr. Sun to disinfect any liquid stored in glass. UV disinfectant pens are a new water purification technology but must be placed inside the container to work.
At a given atmospheric pressure, water heated to boiling in mug inside a microwave is the same temperature as boiling water heated in a kettle. However, don't count on easily getting water that hot in your microwave unless you are prepared to see much of it splatter out of the mug. All the people who think they are observing a scientific phenomenon, i.e. that microwaved substances cool more quickly than those heated by convection or conduction, are making a false comparision. What I think they are actually seeing is that foods heated to lower temperatures in microwaves aren't as warm as foods heated to higher temperatures elsewhere. Add to this the fact that microwaves do not heat ceramics or glass (unless they contain lead) while plates etc. placed under restaurant IR lamps do absorb heat, and you will see why food warmed on plates in a microwave arrives at a table colder than food warmed under IR lamps or placed from a saucepan directly on to a warm plate.

Many of us who make tea in a mug or teapot will put some hot water in the container for a while to warm it up, pour it out, and then pour in the tea-making water. I don't think anyone makes microwaved tea this way.

by rivergal at 3:18 PM on 27 Feb 2007
[ Parent ]

gassy

I'm guessing the gas stove is the way to go, since it doesn't involve the process of converting coal to electricity to heat (at which point you're probably getting about 1% of the energy in the coal) compared to a higher, if not great, percentage for the gas stove.

by TariffDude at 5:03 PM on 27 Feb 2007

first things first

Tea is not supposed to boiled anyway. The water shouldn't be boiled in the first place, just below boiling, and this will preserve the integrity of the tea. This alone could save energy, time and the flavor of the tea.

by masara at 9:13 PM on 27 Feb 2007

First things second

Masara: It's green tea that shouldn't be boiled. If you boil the water for green tea, it gets bitter. Black tea is different.

From the Tetley Tea company:

The key things to remember are to make sure you boil fresh water to more than 98.5 degrees centigrade, as it's only temperatures in excess of this that can efficiently extract flavour from the leaf. Water should be fresh and not previously boiled to maximise the oxygen content. Also, despite a common misconception which dates back to when we all used tea leaves brewed in pots, milk should be added after the tea bag has brewed, otherwise it will lower the temperature from the optimum level and affect the brewing process.

http://www.tetley.co.uk/UK/ThePerfectCuppa/

Ivriniel

by Ivriniel at 12:03 PM on 03 Mar 2007

Tea Time

I can understand the purist view of not using the microwave for water for tea, but I watch my grandchildren, both under two ... need I say more?
How many minutes in the mic for water to reach 180 degrees ... for green tea?
jsk

by jsk at 11:52 AM on 02 Apr 2008

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Darjeeling Companion

On boiling water for tea