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In my experience of buying and using kettles, I have come across none which are insulated.

The obvious reasons as to why it would be beneficial being that heating time would be reduced, similarly, less power hence money would be required to heat an arbitrary volume of water. Some kettles become very hot on the outside so safety is also a factor!

Is there a reason why this is so, apart from the costs involved? I.e. cost of manufacture vs. operating cost over the product lifetime.

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Most kettles are silver to minimize heat loss through radiation. (They also have small exit holes at the top to minimize heat loss of steam because conversion of liquid water to steam requires latent heat)

I expect the reason that there is usually no thermal insulation is that kettles heat water very quickly and because the air outside the kettle is a poor conductor of heat the ammount of heat lost by conduction/convection is probably minimal compared to the ammount of enrgy that goes into the heating of the liquid to make it boil.

By contrast, a hot water tank in a central heating system stores hot water for long periods of time, so it makes sense to carefully insulate hot water tanks.

In summary, I think one way to think about this is that the air outside the kettle is good enough thermal insulation for the short time that the kettle boils the water.

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    $\begingroup$ That said, adding insulation to kettles and measuring the effect quantitatively on energy usage would make an excellent high school science fair project. $\endgroup$ – John Meacham Sep 24 '16 at 23:27
  • $\begingroup$ @JohnMeacham - Hey John - great comment - you could measure the difference in time to boil from cold with and without extra insulation... and do some tests of a hot water tank by simulating it with a cup or insulated cup and pouring in boiling water from kettle and seeing what difference it makes.... +1 for comment :-) $\endgroup$ – tom Sep 24 '16 at 23:48

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