Sir, David Terry (letter, Sept 1) says that boiling a kettle of water with a kettle of half the wattage takes twice as long and so consumes the same amount of electricity. This is approximately true, but ignores the heat loss from the kettle while it comes to the boil. If the kettle takes twice as long to boil the heat loss is doubled and so the lower wattage kettle actually consumes more electricity to boil the same quantity of water.
Peter Dixon
Sheffield