The kettle debate

Zandoni

QrizB said:

Zandoni said:

A kettle on a gas hob seems to use slightly less energy but only if you turn it off when it boils.

More energy but at less cost.

Well yes.

Phlik

anotheruser said:

Ultrasonic said:

There is not debate to be had. No matter how you try to insulate your kettle the water in it will cool down to some extent from when first boiled and so you need to use additional energy to heat it up again.

But what the person is saying is that heating half a kettle of warm water will use less energy than half a kettle of cold water.

It doesn't matter, filling the kettle and reboiling through the day means that by the end of the day you've boiled three times as much water as you need to.

Another way to look at it is this

Boiling two cups of water five times will use (approximately) the same amount of energy as boiling ten cups of water once. So, as soon as you boil that kettle with eight cups (then six cups etc) of water in you are now using more energy than using the two cup method, the number of blankets you wrap the kettle in is irrelevant, you are wasting energy filling the kettle.

QrizB

Phlik said:

anotheruser said:

Ultrasonic said:

There is not debate to be had. No matter how you try to insulate your kettle the water in it will cool down to some extent from when first boiled and so you need to use additional energy to heat it up again.

But what the person is saying is that heating half a kettle of warm water will use less energy than half a kettle of cold water.

It doesn't matter, filling the Kindle and reboiling through the day...

For the benefit of anyone else reading this thread, we don't generally recommend filling your Kindle with water of any temperature.

Phlik

QrizB said:

Phlik said:

anotheruser said:

Ultrasonic said:

There is not debate to be had. No matter how you try to insulate your kettle the water in it will cool down to some extent from when first boiled and so you need to use additional energy to heat it up again.

But what the person is saying is that heating half a kettle of warm water will use less energy than half a kettle of cold water.

It doesn't matter, filling the Kindle and reboiling through the day...

For the benefit of anyone else reading this thread, we don't generally recommend filling your Kindle with water of any temperature.

spotted it after I posted but you were too quick

Section62

Phlik said:

anotheruser said:

Ultrasonic said:

There is not debate to be had. No matter how you try to insulate your kettle the water in it will cool down to some extent from when first boiled and so you need to use additional energy to heat it up again.

But what the person is saying is that heating half a kettle of warm water will use less energy than half a kettle of cold water.

It doesn't matter, filling the kettle and reboiling through the day means that by the end of the day you've boiled three times as much water as you need to.

It does matter because the OP's premise is different to that you've assumed in the rest of your post.  (but for the avoidance of doubt the OP's idea is still not a good one)

Phlik said:

Boiling two cups of water five times will use (approximately) the same amount of energy as boiling ten cups of water once.

This is true if the water is always at the same starting temperature.  The OP isn't suggesting that, and that was anotheruser's point.

Phlik said:

So, as soon as you boil that kettle with eight cups (then six cups etc) of water in you are now using more energy than using the two cup method,

The extra energy needed is only that necessary to reheat the water from the temperature it is at after 'x' hours, which the OP is suggesting would be higher than the starting temperature.  That's valid if the insulation on the kettle is highly efficient and the loss of heat is low.

It is a similar argument to the one about heating a 'huge' hot water cylinder using Economy7 and for the hot water being 'wasted' because the owner only needs a small amount each day.  The standard response to that query is that if the hot water cylinder is well insulated, the cost per day only relates to replacing the lost heat plus heating the volume of replacement water.  If the amount of hot water they use is very small then there comes a point where turning off the hot water cylinder and using a kettle instead makes sense.  The physics and economic principles of the 'great kettle debate' are broadly similar, but with a different outcome.

In practical terms we use E7 for stored water heating because the balance between economic saving and heat-loss works out in favour of heating a large volume and accepting a small amount of heat loss.  We don't do that with kettles because (a) it isn't as practical and (b) heating your kettle in the middle of the night would be a PITB.

Phlik said:

....the number of blankets you wrap the kettle in is irrelevant, you are wasting energy filling the kettle.

It isn't irrelevant.  It is just impractical to insulate to an efficient level.  But insulated kettles will become more of a 'thing' in future.

Alternatively if we had a spherical kettle in a vacuum we could take advantage of minimised heat loss, and the bonus that water boils at a lower temperature at lower pressure....  although the energy consumed to maintain the vacuum would probably wipe out the savings from more efficient heating.  So not practical either.

And colder tea wouldn't taste so good.

QrizB

Section62 said:

And colder tea wouldn't taste so good.

The energy-saving option:
https://en.wikipedia.org/wiki/Cold_brew_tea

Effician

Section62 said:

In practical terms we use E7 for stored water heating because the balance between economic saving and heat-loss works out in favour of heating a large volume and accepting a small amount of heat loss.  We don't do that with kettles because (a) it isn't as practical and (b) heating your kettle in the middle of the night would be a PITB.

We only use about 4l  of boiling water  a day so an immersion heater makes no sense for us, however boiling 4l of water for just under 10p before the E7 goes off at 8am & storing it in Stanley (24hr hot) flasks does .

Phlik

Section62 said:

Phlik said:

anotheruser said:

Ultrasonic said:

There is not debate to be had. No matter how you try to insulate your kettle the water in it will cool down to some extent from when first boiled and so you need to use additional energy to heat it up again.

But what the person is saying is that heating half a kettle of warm water will use less energy than half a kettle of cold water.

It doesn't matter, filling the kettle and reboiling through the day means that by the end of the day you've boiled three times as much water as you need to.

It does matter because the OP's premise is different to that you've assumed in the rest of your post.  (but for the avoidance of doubt the OP's idea is still not a good one)

Phlik said:

Boiling two cups of water five times will use (approximately) the same amount of energy as boiling ten cups of water once.

This is true if the water is always at the same starting temperature.  The OP isn't suggesting that, and that was anotheruser's point.

Phlik said:

So, as soon as you boil that kettle with eight cups (then six cups etc) of water in you are now using more energy than using the two cup method,

The extra energy needed is only that necessary to reheat the water from the temperature it is at after 'x' hours, which the OP is suggesting would be higher than the starting temperature.  That's valid if the insulation on the kettle is highly efficient and the loss of heat is low.

It is a similar argument to the one about heating a 'huge' hot water cylinder using Economy7 and for the hot water being 'wasted' because the owner only needs a small amount each day.  The standard response to that query is that if the hot water cylinder is well insulated, the cost per day only relates to replacing the lost heat plus heating the volume of replacement water.  If the amount of hot water they use is very small then there comes a point where turning off the hot water cylinder and using a kettle instead makes sense.  The physics and economic principles of the 'great kettle debate' are broadly similar, but with a different outcome.

In practical terms we use E7 for stored water heating because the balance between economic saving and heat-loss works out in favour of heating a large volume and accepting a small amount of heat loss.  We don't do that with kettles because (a) it isn't as practical and (b) heating your kettle in the middle of the night would be a PITB.

Phlik said:

....the number of blankets you wrap the kettle in is irrelevant, you are wasting energy filling the kettle.

It isn't irrelevant.  It is just impractical to insulate to an efficient level.  But insulated kettles will become more of a 'thing' in future.

Alternatively if we had a spherical kettle in a vacuum we could take advantage of minimised heat loss, and the bonus that water boils at a lower temperature at lower pressure....  although the energy consumed to maintain the vacuum would probably wipe out the savings from more efficient heating.  So not practical either.

And colder tea wouldn't taste so good.

There's the OP, 

"Only boil what you need(1 cup/2 cups) of water as needed...."

But what if...........say our kettle could hold 10 cups of water, boiled from cold at 8am, 2 cups filled then a cosy keeps the remaining 8 cups warm for 2hrs then boil (from warm) at 12 -which would be quicker from cold, at 2pm boil the 6 cups of warm water (fast), ditto at 5pm (4 cups) 8pm (2 cups)

10 cups of water boiled from cold then 8 cups at 12, 6 cups at 2pm 4 cups at 5pm and 2 cups at 8pm.

The initial 10 cups boiled from cold will use approximately the same amount of energy as if you boiled 2 cups at 8am, 2 cups at 12, 2 cups at 2pm, 2 cups at 5pm and 2 cups at 8pm. So as soon as you need to boil the kettle again for 8 cups worth of water you are using more energy, so no it doesn't matter how many blankets you use, how warm the water is in the kettle, you are using more energy, using the kettle as efficiently as possible is the aim.

It doesn't matter what the temperature of the water is, it could be 80 deg, you are using more energy to heat excess water back up to the desired temperature than is necessary, you are then wasting that energy as the water cools.

I'm not sure why you are comparing it to a hot water cylinder other than they are vessels that hold hot water. A hot water cylinder is a directly or indirectly heated insulated vessel designed for storing hot water for as long as possible as use patterns are variable, so yes it is generally a good idea to keep the heat topped up on a regular basis because of this. A kettle is a directly heated uninsulated vessel for heating water to a specific temperature for immediate use.

Section62

Phlik said:

I'm not sure why you are comparing it to a hot water cylinder...

Then you've missed the whole point.  Not just mine, but most of the one in the OP.

Gerry1

Zandoni said:

Astria said:

Zandoni said:

A kettle on a gas hob seems to use slightly less energy but only if you turn it off when it boils.

Even though most of the heat from the flame with be going into the air rather than heating the kettle which then heats the water?

Sounds perfect in the winter when you need the heat, but not so much when it's warm outside.

Yes it appears that gas is slightly cheaper, have a Google.
https://www.which.co.uk/reviews/cutting-your-energy-bills/article/save-electricity/saving-energy-in-the-kitchen-a9vpj2W40RVJ

Slightly off topic, but note that Which? doesn't always get everything right on techy issues.

'Keep the inside of the fridge between 0 and 5°C, and use a fridge thermometer to check your thermostat is accurate. Lower temperatures decrease energy use, but if it’s too warm your food will spoil.'

Setting the fridge temperature lower will increase energy use !