Small Kettles to save energy

coffeehound

BUFF said:

Personally, I have a kettle which (afaik) has no minimum amount (other than amount being zero - it is a plate type base rather than an exposed coil) & I measure out 300ml of water in a measuring jug when I want to make a cup of coffee/tea before pouring into kettle ...

The flat/solid element types seem to have a high thermal mass compared to the exposed curly elements.  When the power is switched off, they continue to boil for some time after, whereas a coil element stops boiling almost as soon as switched off.  They also seem to have a much shorter working life.

Astria

coffeehound said:

BUFF said:

Personally, I have a kettle which (afaik) has no minimum amount (other than amount being zero - it is a plate type base rather than an exposed coil) & I measure out 300ml of water in a measuring jug when I want to make a cup of coffee/tea before pouring into kettle ...

The flat/solid element types seem to have a high thermal mass compared to the exposed curly elements.  When the power is switched off, they continue to boil for some time after, whereas a coil element stops boiling almost as soon as switched off.  They also seem to have a much shorter working life.

Whilst I agree with your first statement, please define "much shorter working life", as I've had mine since 2017 and it's still working?

coffeehound

Just from personal experience, I've had the same curly element kettle used a couple of times a day, almost every day for the past 11 years.  Over the same period, my parents must have got through seven or eight flat-element kettles, including some fairly expensive ones - usually with the element going pop

Grizzlebeard

BUFF said:

Grizzlebeard said:

If the "kettle" had zero thermal mass you only need energy to heat the water alone.
If the kettle has the same thermal mass as the water half the energy heats the water and half the energy heats the kettle - using twice the total amount of energy.
By way of illustration, if the kettle had nine times the thermal mass of the water then only 10% of the energy used would be going into the water and 90% into the "kettle".
QED: a smaller (thermal mass) is the more efficient.

Heat retrieval for the next cuppa is a different question but it will never be an 100% efficient process in practice anyway.

Other things being equal, my plastic kettle (lower thermal mass) boils quicker than my stainless steel (higher thermal mass) kettle but I currently use a 1 pint aluminum camping kettle on the gas stove.

Even then though as long as the kettle is not full you aren't heating all the thermal mass evenly. That kettle body in direct contact with the heated water is likely to be heated higher than that outwith contact with the water which will be heated via conduction through the body - plastic conducts heat less well than metal so a bit of a win on the materials front there for a plastic bodied kettle.
Snip

That's very true BUFF. But also to be considered is that the larger kettle has more radiating/convectioning surface area so will lose heat to the environment more quickly. But working out the true balance of heat gain/loss in various situations would require solving more mathematical functions than I have remaining in my very old brain. (Vague recollections of the area under a function curve and infinitesimal integral calculus is best I can do.)

Anyway as a general statement turning down the CH 0.5C will save more planet than all the theoretical kettle savings possible. (Unless perhaps you're running a very busy cafe.)

Sea_Shell

Just to throw another variable into the mix...

We're in a hard water area, so we get limescale build-up.   This ends up with added crunch in your coffee, if you only boil exactly what you need.  So I do overfill slightly, to avoid the dregs.  The filter isn't perfect!!

We descale regularly, once we notice it's getting bad.   But this also has a cost, which if done more often may outway the benefits of boiling that little bit extra.

Discuss. 😇

Petriix

coffeehound said:

The diddy kettles tend to be low power, perhaps a quarter the power of a 3-pint kettle, so you'd be waiting four times as long each time you boil (and losing heat during that time as well).  That could be a deal-breaker.

On the other hand, for those of us with solar panels, running a kettle at 800W rather than 2.4kW is more likely to be able to run on surplus solar energy at this time of year so it's probably better.

molerat

Astria said:

coffeehound said:

BUFF said:

Personally, I have a kettle which (afaik) has no minimum amount (other than amount being zero - it is a plate type base rather than an exposed coil) & I measure out 300ml of water in a measuring jug when I want to make a cup of coffee/tea before pouring into kettle ...

The flat/solid element types seem to have a high thermal mass compared to the exposed curly elements.  When the power is switched off, they continue to boil for some time after, whereas a coil element stops boiling almost as soon as switched off.  They also seem to have a much shorter working life.

Whilst I agree with your first statement, please define "much shorter working life", as I've had mine since 2017 and it's still working?

2017, pah, mine is definitely pre 2009

BUFF

Grizzlebeard said:

That's very true BUFF. But also to be considered is that the larger kettle has more radiating/convectioning surface area so will lose heat to the environment more quickly. But working out the true balance of heat gain/loss in various situations would require solving more mathematical functions than I have remaining in my very old brain. (Vague recollections of the area under a function curve and infinitesimal integral calculus is best I can do.)

Yup, it's a case of just how far down this tunnel of variables do you want to go ...
Is it worth the hassle to go there - definitely not for me! 

p.s. I (sadly) looked up when I bought this kettle - 2013

Grizzlebeard

molerat said:

Astria said:

coffeehound said:

BUFF said:

Personally, I have a kettle which (afaik) has no minimum amount (other than amount being zero - it is a plate type base rather than an exposed coil) & I measure out 300ml of water in a measuring jug when I want to make a cup of coffee/tea before pouring into kettle ...

The flat/solid element types seem to have a high thermal mass compared to the exposed curly elements.  When the power is switched off, they continue to boil for some time after, whereas a coil element stops boiling almost as soon as switched off.  They also seem to have a much shorter working life.

Whilst I agree with your first statement, please define "much shorter working life", as I've had mine since 2017 and it's still working?

2017, pah, mine is definitely pre 2009

Pre 2009? pah, my camping kettle dates from when I was a student in the 1970s! Remember it well. I'd just moved into a slightly sturdier cardboard box with flaps that would actually close.

(Jeez!! Just realized some days I spend way too much time on this forum! No wonder my neglected house is as creaky as Castle Gormenghast.)

coffeehound

Petriix said:

coffeehound said:

The diddy kettles tend to be low power, perhaps a quarter the power of a 3-pint kettle, so you'd be waiting four times as long each time you boil (and losing heat during that time as well).  That could be a deal-breaker.

On the other hand, for those of us with solar panels, running a kettle at 800W rather than 2.4kW is more likely to be able to run on surplus solar energy at this time of year so it's probably better.

Fair point.  Also boats and caravans are limited on power, so the small kettles have their place