Boris Johnson and money saving kettles.

Might be good enough for coffee, but not tea.

CliveS said:

This saves all the heat losses that normal kettles emit as the remaining water cools down and give you a reserve for a coffee later.

Lisa, The instant hot water is very efficient but 7 kW is like the electric shower quite slow in filling a teapot and tricky to get up to and maintain at boiling point.  Constantly on expensive hot water taps may be ideal at saving time but if they keep turning themselves on and off then they are loosing energy all the time and their insulation needs improving.

The best way to save energy is to purchase a vacuum flask and boil your kettle to fill your teapot and the flask at the same time.

This saves all the heat losses that normal kettles emit as the remaining water cools down and give you a reserve for a coffee later.

I take the point, but are you saying that all heating elements are as efficient as each other?

Where do the 'instant hot water' taps sit here though? Are they more or less efficient than boiling a traditional kettle? 

More likely, it's about thermal conductance between the element and the water.

Sounds plausible - an element covered with limescale is going to take longer to heat up the water. It's not that less heat is generated - just it's harder to get that heat into the water, so the element itself contains more of the heat (i.e. is hotter) when boiling finishes. Unless the kettle is immediately re-filled and boiled again, the extra heat in the element will be gradually lost to the surroundings.

     - Andy.

or at least the fact that some of the heat is lost to the environs - a shiny metal kettle will lose less than a dull one. Worst would be matt black like a heatsink, luckily not that common....  Also note that there is a fair old variation between 'identical wattage' elements. The factory do not like rejects, so almost anything goes out the door.

Mike.

If some of the electrical energy isn't being turned into heat, then it must be turned into something else.  That seems unlikely in a kettle.

More likely, it's about thermal conductance between the element and the water.

I have never fully understood why, but some kettles are faster than others of the same wattage. I suspect that some are more efficient than others when it comes to changing electrical energy into heat.

If Boris is referring to the older all metal kettles,would they not lose more heat before

boiling compared to plastic kettles?

                                                      Hz

Any other energy saving kettle features?

I reckon many are a bit slow at automatically switching off when they get to the boil - especially when boiling small amounts of water and steam seems to have to fill most of the remaining space before triggering the sensor. There's room for improvement there I reckon.

    - Andy.