. . . back to part 3 . . .

How much is inside hot water? - part 4


gas method kettle method
Uses 0.3 kWh of chemical energy
Uses 0.36 kWh of chemical energy
Delivers: 0.11 kWh of hot water
Delivers: 0.11 kWh of hot water

0.19 kWh of heat in your kitchen
0.06 kWh of heat in your kitchen
0.19 kWh of heat in the cooling tower and electricity network

In the winter, or at any time when you want to warm your kitchen, I firmly recommend using the gas method to make your hot water. Yes, the hob-with-saucepan is inefficient - only about 37% of the energy from the gas gets into the water(*); but the rest of the energy gets into your kitchen, so it's not wasted.
On a summer day, when you don't want extra heat in your house, I would probably recommend using the kettle method. It uses slightly more chemical energy, but it has the advantage of not making the kitchen sweaty.

(*) It's a coincidence that the hob-with-saucepan has the same efficiency - roughly 37% - as the power station and electricity network. For the record, the power dissipated by the gas hob was (0.3 kWh in about 5 minutes) about 3.6 kW.

This used to be the end of this story.

But, owing to popular request, I did two more experiments. Keep reading if you wish...

Dasher - efficient communication with any muscle

Tapir - a simple 12-key disambiguating keyboard.


This page is a tribute to cockeyed.com

To find out more energy numbers, you might like to read my book Sustainable Energy - Without the Hot Air.

David MacKay
Last modified: Tue Jun 24 00:56:10 2008