Boiling a Kettle

It is easy to be mislead by advertisers' claims for environment advantages of their products - in this case boiling water in a kettle. We will look at the environmental claim and see what parts are true and which parts are misleading.

The following claim was made for an "Electric Eco Kettle":

Until now, accurately measuring the amount of water to be boiled in your kettle has been all but impossible. The result? It is estimated that, on average, we boil twice the volume of water needed every time. Which means twice as much energy, twice as much time. With a 3kW kettle that's the same as wasting the energy of around 50 light bulbs!

Most of this claim is true except for the phrase With a 3kW kettle that's the same as wasting the energy of around 50 light bulbs!

For the energy to be wasted, it has to have no use. One time when the energy is wasted is when the kettle is used outdoors. The energy that was used boil water that was not required will transfer from the very hot water to the atmosphere as the water cools. This transfer of energy serves no purpose than to warm the outdoors and contribute to global warming and climate change.

If, on the other hand, it is summer and the kettle is used indoors, the question is where does the energy that was used boil water that was not required transfer to. In summer, in a house with windows open to aid cooling, the energy will again be transferred to the atmosphere as the water cools. This transfer of energy serves no purpose than to warm the outdoors and contribute to global warming and climate change.

So, when the kettle is used outdoors or in the summer time, the claims are true. But what about using the kettle indoors in winter. In this case, the energy that was used boil water that was not required is transfers to the living space of the house. This helps warm the house and the energy demand of the heating system is reduced by the same amount. This means that, looking at a home holistically, there is no reduction in energy usage when boiling more water than necessary during the summer month.

If you were to buy an "Electric Eco Kettle" and expect to see your energy use reduce throughout the year, you will be disappointed as the savings only occur in the summer months. The advertising claims would imply energy saving of half the electricity used with a non-eco kettle. In actual fact the savings are only about ¼ of the electricity used with a non-eco kettle.

This use of energy to heat a home could be a useful by-product of heating water. The effect is known as "The Heat Replacement Effect" and there was a report to the UK Government on The Heat Replacement Effect. It stated that "The energy and carbon savings attributed to better home appliances and lighting are not fully achievable because less heat is given up to the building in which they are installed. In the winter, the heat from appliances and lighting is “useful”, and if it is reduced the deficit will be made up automatically by the thermostatically controlled heating system (usually a gas boiler and radiators). The effect is significant, and should be taken into account when estimating the benefits from energy saving measures in national energy efficiency policies and programmes."

CO₂ Emissions

When it comes to CO₂ emission, the situation is far more complex. Energy from electric power stations in the USA creates, on average, around three times the CO2 than energy from natural gas. In the UK, energy from electric power stations creates around twice the CO₂ than energy from natural gas. The difference between the USA and UK is due to the different mix of fossil fuels used to generate electricity and the amount of nuclear and wind power generation. Indeed, even in the USA there is a large range of CO₂ emissions values per unit of energy with some states, like California, creating less than the average CO₂ emissions per unit of energy while others, like Pennsylvania, creating more than the average CO₂ emissions per unit of energy.

For homes that are heated by electricity, any savings in total electricity use is matched by a corresponding reduction in CO₂ emissions. For homes that are heated by natural gas - the least polluting of the fossil fuels - there are CO₂ emission reductions to be make by not using any more electricity than absolutely necessary. Any increase of gas heating energy that has to replace the reduction of heat from electrical devices creates less CO₂ emissions. For example in the UK a saving a one tonne of CO₂ emissions created by heating more water than necessary using an electric kettle requires a gas heating system to create half a tonne of CO₂ emissions to replace the lost heat.