Electric Kettle or Gas?

Ben84

Cardew wrote: »

Although watt hours is a perfectly acceptable term, as we are billed for kWh it tends to be a convention when talking of electrical consumption in domestic properties to use kWh even when fractions of a kWh are used.

i.e. a 60 watt bulb on for two hours would be described as using 0.120kWh instead of 120 watt hours - although both terms are obviously correct.

In the same way the average annual consumption of a domestic property is 3,300kWh. It would be unusual for that to be described as 3.3MWh(3.3 megawatt hours)

Thanks Cardew, that makes sense. I think a better method for what I described would be that a 3000W kettle, if run for an hour would use 3 kWh, so I just need to time how long it takes to boil (224 seconds) then find what fraction of 3 kWh that represents. 3600 / 224 = 16 instances of 224 seconds in an hour, then divide the 3 kWh by 16. So, 3 kWh / 16 = 0.1875 kWh. That can be multiplied by the cost of electric per kWh to find a price.

Anyway, turning it in to kWh right from the start does seem easier and more helpful.

rogerblack

Ben84 wrote: »

Induction hobs, although more efficient that other hobs, still have to heat the pan before the water inside it.

But.
(there always is a but, isn't there)

I just did a test, with a small stainless bowl on my induction cooker.
The power meter read 1.9kW or so, and it took about 55s to boil 200ml.
The kettle used 2.2kW, and took about 50 seconds.

So, this quick test - which is not very accurate gave a possible slight margin to the cooker, though it's not really easy to say, as there may be other issues. (I am unhappy about the accuracy of the meter used).

One reason was the bowl I used was a very light one, and most of it was not in contact with the water, so a very limited amount got heated up.
Perhaps 30 grams total - equivalent to about 3 grams of water.

Another is that on the kettle side - the element is quite heavy, as are the plastic walls - the amount of total stuff heated is higher, and plastic is about 4* harder to heat.

It's interesting to note that my coiled element kettle, with the element just wet with water, only gets hot enough to boil water off the surface after 7 seconds.
The bowl - about 1.

If a pan is 4* heavier than a (plastic) kettle, it's likely to use less energy to heat it.

I think my earlier recommendation of a tiny lightweight stainless steel kettle is probably best. I may try this when I get my tabletop induction cooker working again, so I can do proper measurements.

Ben84

rogerblack wrote: »

But.
(there always is a but, isn't there)

I just did a test, with a small stainless bowl on my induction cooker.
The power meter read 1.9kW or so, and it took about 55s to boil 200ml.
The kettle used 2.2kW, and took about 50 seconds.

So, this quick test - which is not very accurate gave a possible slight margin to the cooker, though it's not really easy to say, as there may be other issues. (I am unhappy about the accuracy of the meter used).

One reason was the bowl I used was a very light one, and most of it was not in contact with the water, so a very limited amount got heated up.
Perhaps 30 grams total - equivalent to about 3 grams of water.

Another is that on the kettle side - the element is quite heavy, as are the plastic walls - the amount of total stuff heated is higher, and plastic is about 4* harder to heat.

It's interesting to note that my coiled element kettle, with the element just wet with water, only gets hot enough to boil water off the surface after 7 seconds.
The bowl - about 1.

If a pan is 4* heavier than a (plastic) kettle, it's likely to use less energy to heat it.

I think my earlier recommendation of a tiny lightweight stainless steel kettle is probably best. I may try this when I get my tabletop induction cooker working again, so I can do proper measurements.

Induction hobs, lightweight kettles, I'm still using a big heavy chromed steel and bakerlite kettle from approximately 1980. I never thought there was any real difference in energy use, but it does make sense now that some may have more energy losses than others. Is it enough to make a noticeable difference on the bills though? My kettle is used about 5-10 times a day, meaning from my earlier calculation we use about 10-20p a day for the kettle, so about £30-70 a year! It seems like a lot when you look at it for a whole year.

Also, I'm not surprised the kettle element appears a bit slower. If you've ever accidentally turned on a kettle without any water, you might have been unlucky and caused the element to burst. Well, if you don't have one of the kettles that fires the cable out before it seriously overheats. Anyway, I did this once with a very old kettle and discovered how the element is made. There's an inner core of resistant wire that heats up, surrounded by a white powder which is I believe alumina - a fairly good thermal insulator, then a steel tube which is the element we see inside the kettle. The alumina will slow down the heat emitted by the element when first turned on.

zeupater

rogerblack wrote: »

But.
(there always is a but, isn't there)

I just did a test, with a small stainless bowl on my induction cooker.
The power meter read 1.9kW or so, and it took about 55s to boil 200ml.
The kettle used 2.2kW, and took about 50 seconds.

So, this quick test - which is not very accurate gave a possible slight margin to the cooker, though it's not really easy to say, as there may be other issues. (I am unhappy about the accuracy of the meter used).

One reason was the bowl I used was a very light one, and most of it was not in contact with the water, so a very limited amount got heated up.
Perhaps 30 grams total - equivalent to about 3 grams of water.

Another is that on the kettle side - the element is quite heavy, as are the plastic walls - the amount of total stuff heated is higher, and plastic is about 4* harder to heat.

It's interesting to note that my coiled element kettle, with the element just wet with water, only gets hot enough to boil water off the surface after 7 seconds.
The bowl - about 1.

If a pan is 4* heavier than a (plastic) kettle, it's likely to use less energy to heat it.

I think my earlier recommendation of a tiny lightweight stainless steel kettle is probably best. I may try this when I get my tabletop induction cooker working again, so I can do proper measurements.

Hi

Methinks a little self-review of the logic and interpretation utilised is necessary here .... it's either that or the wording of the post ....

HTH
Z

rogerblack

zeupater wrote: »

Hi

Methinks a little self-review of the logic and interpretation utilised is necessary here .... it's either that or the wording of the post ....

HTH
Z

It seems to make sense to me - can you point out the silly bits, in your opinion?

zeupater

rogerblack wrote: »

It seems to make sense to me - can you point out the silly bits, in your opinion?

Hi

I'd be pretty concerned with the thermal conductivity of metal vs plastic & the relative thermal mass of the containers to the water.

Stainless steel will conduct heat much faster than plastic, plastic being a relatively good insulation material compared to steel. Relative to water the steel will be in excess of 8x the mass per unit volume and plastic will be 1.x (the plastic will only weigh more than steel if it 8.x/1.x times thicker) .... The bowl will therefore conduct heat much further up the metal sides than the area directly in contact with the water and therefore act to increase the to air heat transfer surface.

I believe what you are seeing is the effect of the thermal mass and thermal transfer gradient within the kettle element on the heating time for the water ... you could establish the extent of this by conducting the same experiment with double the volume of water which would half the effect of the element itself per unit volume ....

Looking at the 'plastic is 4x harder to heat' .... I would have thought that what is really meant is that for a given thickness, the temperature gradient for heat transfer from one side to the other would be a number of times lower for plastic than metal, however, once both materials have reached temperature saturation (say 100C), they will be 100C on the inside and, due to the rate of heat transfer through the material and the ambient temperature, slightly below 100C on the outside.

What you have seen when heating droplets of water on the kettle element vs the bottom of your thin stainless steel bowl is again a factor of thermal mass ... if your bowl was to be a heavier gauge then it would also absorb more heat, therefore, if you were to compare pan vs another which is 4x heavier then there would be 4x the thermal mass .... the same would be true for a metal pan vs a plastic container which is 4x the mass - what would then need to be considered is the relative heat capacity of the materials per unit of mass .....

It's very likely that in a situation where two kettles which are identical apart from the container materials (one plastic/one metal) the plastic would be considerably thicker than the stainless steel, but this would likely be less than 8.x/1.x on thickness therefore it should be lighter ... add to this the relative insulating quality of the plastic then the plastic kettle should prove to absorb less heat over the time taken to boil the water from cold and should therefore be more efficient ....

HTH
Z

MiserlyMartin

moonrakerz wrote: »

A small electric kettle with an exposed element close to the bottom of the water jug is about as near to 100% efficient for heat transfer as you can get.

A gas flame is not only having to heat the kettle before any heat gets to the water but it's heating the hob, the kitchen, you, etc, etc..

Also, if it's started whistling, you are wasting energy on that !

I keep seeing mentions of low efficiency from gas hob kettles. That would be true in a heatwave when the house is already too warm, but for most of the year, any extra heat generated by a gas kettle all goes towards heating the house so it's not a waste at all!

I wonder how long it would take to make my money back from the outlay of buying a gas whistling kettle?

Margo1_2

What about the type of kettle used on a gas hob - cast iron, aluminium, stainless steel etc. I have heard aluminium is the best heat conductor???

rogerblack

Margo1 wrote: »

What about the type of kettle used on a gas hob - cast iron, aluminium, stainless steel etc. I have heard aluminium is the best heat conductor???

Aluminium will be slightly more efficient - as the lower the temperature of the surface of the pan, the more efficient is the heating.
It's a very small factor, and a thin stainless kettle may be better than a thick aluminium one, as the whole mass of the kettle has to be heated.

In practice, it's going to be barely measurable.

TheBearNecessities

electric hob v's electric kettle anyone?