heating water...

[VJ]

Hello!

We have the electric kettle, but it broke down. So we should replace it. However, we've noticed that we can boil the same amount of water almost 3 times faster on our induction cooking plate (in a pot).

And it made us wonder: what is the most energy efficient way of heating water? Induction cooking plate or electric kettle?
(We cannot use a simple power meter, as the induction plate is on 3 phase power.)

Of course, there are other arguments: electric kettle switches off automatically, takes up space on worktop and takes a socket; induction would be faster, but does not switch off by itself (we can set a timer) and takes up a cooking plate (but we have 4 and never use them all). But we just got curious on the power issue... :-)

Any thoughts?
Induction-plate or heating element?

Jörg

[dZeus]

Hello!

We have the electric kettle, but it broke down. So we should replace it. However, we've noticed that we can boil the same amount of water almost 3 times faster on our induction cooking plate (in a pot).

And it made us wonder: what is the most energy efficient way of heating water? Induction cooking plate or electric kettle?
(We cannot use a simple power meter, as the induction plate is on 3 phase power.)

Of course, there are other arguments: electric kettle switches off automatically, takes up space on worktop and takes a socket; induction would be faster, but does not switch off by itself (we can set a timer) and takes up a cooking plate (but we have 4 and never use them all). But we just got curious on the power issue... :-)

Any thoughts?
Induction-plate or heating element?

Jörg

The 3x faster argument is a simple matter of greater power output.

I think both are near 100% efficient in converting electrical energy into heat. With the induction plate, you're also heating the metal pan which probably absorbed more thermal energy than the kettle does, so my guess is that the electric kettle wins (if its shell is made of a poor thermal conductor such as some form of plastics).

[VJ]

Yes, the 3x faster is another argument... phrased it wrong... :-) The basic question was: for heating e.g. 1 l of water, which of both would consume less energy?

But your say that on the plate you also heat the pot is interesting... :-) The thing is: it is an induction plate, so the base of the pot is heating up as a result of the induction. It is not like on an electrical cooking plate where heat first has to be transferred to the base, and then to the water.
But more heat might be lost through the walls of the metal kettle than through the walls of the electric kettle. Seems like a valid point...

[cjolley]

For the same amount of water the kettle might use less because, no pot to heat and, ours at least, is kind of insulated so less heated air.

Auto off is IMPORTANT.
Plus better pouring spout.
And really, admit it, there is something relaxing about putting on a kettle of water. Pot not so much...

[UtwigMU]

I managed to melt electric kettle ^_^ Don't ask me how Acetone is great for molten plastic clean-up.

My method of cooking is to put empty pot on stove and heat it up, while boiling water in the kettle

Borrow electric power measurer - the one you plug stuff in and see how much power kettle or stove consume. Then time both to boil 1l of water at same temperature and multiply power with time to get Wh.

[cjolley]

I can tell you exactly how.
Those kettles depend on the lid being closed properly for the auto-off to work.
Leave it even slightly ajar and it will just boil all the water away and keep going

[UtwigMU]

I can tell you exactly how.
Those kettles depend on the lid being closed properly for the auto-off to work.
Leave it even slightly ajar and it will just boil all the water away and keep going

Actually I placed it on hot electric stove that I forgot was hot. Kitchen filled with smoke, plastic melted over the stove. Flatmate didn't freak out although it was her kettle.

[cjolley]

Actually I placed it on hot electric stove that I forgot was hot.

LOLZ, that will definitely do the trick

[Brian Ellis]

To heat a given volume of water from, say, 15°C to 95°C (no boiling) will always require the same number of joules (or Wh), no matter how it is done. Any difference between two methods will be functions of the thermal mass of the recipient up to the water level, the efficiency of the heating method (heat transfer: an immersion heater in a kettle will be nearly 100%), heat losses to the air over the time (the quicker the better), the heat losses due to heating the recipient and lid above the water level, the heat losses due to evaporation, less the gain due to condensation.

Actually boiling the water slightly changes the equation because the extra energy supplied will depend on the rate of evaporation or the power input, as a function of the heat losses. IOW, time to evaporate n grams of water will vary.

All in all, I would estimate that a well-designed kettle will be more efficient. If you find induction heating in a pot with a lid is faster, for a given volume of water, this is almost surely because the heater transfers more energy into the water, and therefore consumes more energy from the power supply.

[VJ]

Auto off is IMPORTANT.
Plus better pouring spout.
And really, admit it, there is something relaxing about putting on a kettle of water. Pot not so much...

Well, I would compare an electric kettle to a traditional kettle on an induction plate (not a pot - but at the moment this is the best we have).
Auto off is convenient, that is true. :-)
Induction (with a good pot) is ridiculously fast though (one single plate can go up to put 4kW). Not sure induction-compatible kettles would be *that* good as a good cooking pot - a lot depends on the construction of the bottom of the kettle.

Borrow electric power measurer - the one you plug stuff in and see how much power kettle or stove consume. Then time both to boil 1l of water at same temperature and multiply power with time to get Wh.

The cookingplate is on 3-phase power, hardwired, so no possibility to do that; the resolution of the electricity meter is too low to get accurate readings.

Leave it even slightly ajar and it will just boil all the water away and keep going

Auto off is what is failing on our current kettle... We noticed it when the kitchen window was all steamed up. :-)

Any difference between two methods will be functions of the thermal mass of the recipient up to the water level, the efficiency of the heating method (heat transfer: an immersion heater in a kettle will be nearly 100%), heat losses to the air over the time (the quicker the better), the heat losses due to heating the recipient and lid above the water level, the heat losses due to evaporation, less the gain due to condensation.

Yes, it is those differences I was curious about... Most electric kettles now don't have exposed heating elements, so I assume that lowers their efficiency (otherwise they would more resemble immersion heaters).

All in all, I would estimate that a well-designed kettle will be more efficient. If you find induction heating in a pot with a lid is faster, for a given volume of water, this is almost surely because the heater transfers more energy into the water, and therefore consumes more energy from the power supply.

Yes, but it does so for a shorter time...

[Brian Ellis]

Yes, but it does so for a shorter time...

Which electricity bill is cheaper: 3 kW kettle on for 3 minutes or 5 kW induction heater on for 2 minutes?