# A little OT: electric kettle versus kettle on induction ring

My solar installation is limited to 5kW. It can go to 7 for a bit, but I try to avoid it. Trouble is, our kettle uses almost 3kW. So if the water heater is on and the aircon etc. at the same time, we can have problems.
I noticed that our new induction hob has a "boost" facility which makes a pan of water boil very quickly. I'm pretty sure it consumes at a lower rate than the kettle. Is this possible? I would have thought a kettle with submerged element would be nigh on 100% efficient.
Opinions?
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Paul.
https://paulc.es
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On Thursday, 16 June 2016 17:32:14 UTC+1, Paul wrote:

A kettle with a submerged element is nigh on 100% efficient.
You will have to check the hob instructions for details of its consumption at various powers.
If you want to reduce instantaneous load, get a smaller and lower-wattage kettle for occasional cuppas.
Owain
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On 16/06/2016 18:40, snipped-for-privacy@gowanhill.com wrote:

ISTM both are 100% efficient at converting energy from electrical to heat. The problem is how much of that energy goes "usefully" to raise the water to boiling and how much is "wasted" by way of heating the kettle itself, the hob, the worktop, and the room generally by way of evaporation, convection, conduction, radiation and noise. So I'd think a first order test would be to put the same amount of water in each kettle and let them come to equilibrium at the same temperature. Then time how long each takes to boil the water. Multiply those times by the power of each (as a first approximation the rated power) to give a relative[1] measure of efficiency with the lower figure the better.
<envy_mode? Or - since you are living with solar power - forget efficiency of boiling water and open a bottle of something cool :)
[The same mass of water is raised by the same temperature using the same energy.
If the hob's power is P1 kW and the kettle's P2 and they take times T1 and T2 respectively to boil the water then the *total* energy each used - including waste - is P1 x T1 and P2 x T2. SO the more efficient is the one with the lower PxT figure.]
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Robin
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wrote:

That reads as if solar is your only source of electricity. Surely not, or are you out in the sticks with no mains supply?

Induction hobs have an efficiency of around 72%*, but a kettle should be pretty close to 100% as you say, so if your hob boils water faster than the kettle boils the same quantity of water, then your assumption that the hob uses less power must be incorrect. * http://tinyurl.com/jvx8efc
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Chris

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Chris Hogg wrote:

Spain IIRC.
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Chris Hogg wrote:

We have gone off grid. In Spain they decided to tax sunlight, so we threw the fuse.

I'll have a look later for interest's sake, but it sounds so far like my basic hunch was right ie; the kettle will be more efficient.
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Paul.
https://paulc.es
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On 16/06/16 17:32, Paul wrote:

The kettle is more efficient as you say - the only 2 losses from that system are:
1) Heating of the supply cables;
2) Some loss to the air through the wall of the kettle.
Otherwise, it's practically a perfect system.
However, the induction cooker on metal boost will do the job extremely quickly. But I suspect there will be some losses from the electronics as heat and could even be some small losses as eddy currents in more remote metalwork.
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On Thursday, 16 June 2016 20:25:52 UTC+1, Tim Watts wrote:

so the walls of the kettle don;t get hot. news to me. Steam never comes out of teh kettle.
yuo know why steam is an efficint clearer don;t you. It''s the energy it holds and when it comes out of the spout of your kettle it's lost.

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Then do not use them all at the same time.
How do you make a brew at night?
What happens if you cook a dinner?
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ARW wrote:

I already have the water heater on a timer so it's only on during sunlight hours, but on a hot summer day, we may have the aircon on at midday and fancy a cup of tea.

Put the kettle on.

Well, yes, every evening the usage peaks at around 5kW. We avoid making tea while dinner is cooking.
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Paul.
https://paulc.es
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What you need is some way to turn the water heater off when running the kettle.

No it doesn't if it boils the same quantity of water quicker.

Nope.

Correct.

Facts are better.
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Well, kettles elements are insulated, so that insulation has tobe heat conducting. The surface area of the element cannot be as great as the bottom of a pan, and you have thermal churning in both systems to be able to get the water uniformly hot. As you say though, induction through a gap should one would imagine be far lessefficient overall. Brian
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On Thursday, 16 June 2016 17:32:14 UTC+1, Paul wrote:

The way to go is to get a jug instead of a kettle. They are lift off (the base) too. You can boil the precise amount of water you need (They have a measuring scal, often takes only seconds. Boils very small quantities if that's all needed. Usually they have a smaller (in Kw) heating element than a kettle.
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harry wrote:

I thought all modern electric kettles were "jugs".
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Paul.
https://paulc.es
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They are kettles = jug kettles
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from KT24 in Surrey, England

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On Friday, 17 June 2016 08:49:12 UTC+1, harry wrote:

I have a jug gettle which is 3kw.
can anyone explain why the case of rthe kettle gets hot and reamins hot for a while after the water is gone. And where does the ENERGY comes from to heat the kettle (rather than the water) and where the ENERGY comes from to create the steam that comes out of my kettle ?
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On 17/06/2016 11:51, whisky-dave wrote:

OK but you have to supply some information..
what's it made from what's the wall thickness what's the dimensions what is the surface texture are there any draughts how much water do you boil how much is left how long between boils

That's the easy one.. the sun and a supernova.
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On 16/06/2016 17:32, Paul wrote:

You make it sound as if the "boost" comes from magic!
All that happens, so far as I am aware, is that some induction rings allow themselves to be over-run for a few minutes.
A ring rated at, say, 1.8 kW, would run at 2.7 kW for five minutes. Or something like that. At the end of the over-run it will revert to standard rating. So using boost wouldn't help you significantly reduce your maximum loading.
On a typical four ring hob, you'll probably find that only two rings at a time can be on boost.
I really doubt a kettle can be beaten for efficiency.
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Rod

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On 17/06/2016 08:51, polygonum wrote:

Different kettle designs may have different efficiency. The obvious one is to make them tall and narrow so you can heat less water and to have a flat element in the base rather than the rings in old style kettles. And you can insulate them to make them safe to touch as well as potentially saving energy.
And alternative is a one cup dispenser of which there are two types.. one that puts out a flow of near boiling water that is suitable for coffee but not real tea and the other that puts out a whole cup of boiling water that is OK for tea but maybe a bit hot for coffee.
They are probably both more energy efficient than a kettle if they dispense the correct quantity.
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On Thursday, 16 June 2016 17:32:14 UTC+1, Paul wrote:

I donl;t understand how a kettle can be clos eto 100% efficient. My kettle is just over 3KW after I;'ve boiled it I can burn my hand on it;s plastic case even the handle gets warm. I aslo see steam coming out of teh lip. I assume this heat is effectively wasted as it doesn;lt end up in my cup of tea.
So other than my physics teacher explaining on the latent heat of evapouration of water and how using a calorimeter or a dewer flask can anyone explan to me how a standard kettle can be anywhere near 100% efficient ?
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