Which is more energy efficient – boiling water in kettle from cold or with hot from tap?
It really depends. If your water heater is far away from your kitchen and you have to run a bunch of water before it gets hot, then it is more efficient to use cold. The reason for this is that you have to fill the pipes with hot water all the way from the water heater to the kitchen thus requiring a lot more hot water than the kettle holds. If you have already run the hot water for other reasons then it may be better to use hot water since your hot water heater may be more efficient than your kettle.
