To save energy, many households use kettles as an alternative to gas or electric stoves. It's usually the right choice for a cup of tea, but does it also apply to pasta water?
In the past few months, many different tips for saving energy have been read, seen or heard. Not all of them are correct or apply in principle. Sometimes things get a little more complicated, for example when it comes to heating pasta water as efficiently or cheaply as possible.
It has stuck in many people's minds that kettles heat water more energy-efficiently than is possible in tea kettles or pots on electric or gas stoves. But you can't say that in general, it mainly depends on the amount of water that is brought to the boil.
With a cup of tea or other small amounts of water, the kettle always has the edge, as Stiftung Warentest determined back in 2012 (magazine article). Accordingly, it heats a liter of water about twice as fast as a conventional stovetop and uses only about half the energy. A glass ceramic hob performs only slightly better, a microwave takes four times more time than a kettle and twice the amount of energy.
An induction hob (without a booster) turned out to be almost equivalent in a product test, which was only a little slower, but above all consumed hardly any more electricity. Since kettles have remained technically almost unchanged in recent years, but induction hobs now probably work more efficiently, the race could be even closer today. In any case, the difference is negligible.
Gas stoves already played a special role in 2012. Because bringing a liter of water to the boil requires almost two and a half times more energy on the flame than with a kettle. At 7 cents per kilowatt hour (kWh) for gas and 27 cents for electricity, the pot on the gas stove was by far the cheapest way to heat water at the time.
According to the Federal Association of Energy and Water Industries (BDEW), households with an annual consumption of 20,000 kWh currently pay an average of around 20 cents/kWh. For a kilowatt hour of electricity with an annual consumption of 3500 kWh, you now pay an average of just under 40 cents. This means that a kettle not only uses less energy than a gas stove to heat a liter of water. It also does this a little cheaper and ideally with a much better CO2 balance.
This is why kettles are now also used in many households to boil larger amounts of water, for example pasta water. In this case, however, the kettle is additionally heated, which wastes energy, writes "Ökotest". In addition, heat is lost to the environment during pouring and through the cold saucepan. "Physically, it should be a zero-sum game at best," and that's why it's best to heat pasta water right away in the pot, if possible on economical induction surfaces.
Gas stoves are not as energy efficient as induction stoves. But with larger quantities, it comes into play that they are immediately at operating temperature and heat pots directly, just like with induction. For longer cooking times, it doesn't matter whether you heated the water in the kettle beforehand or not.
The question that remains is whether it is worth using hot water from the tap for cooking. In most cases, cold water is preferable, writes "Utopia", citing the consumer center in Berlin. Modern kettles heat the desired quantity very specifically and directly on site. Hot water from the boiler, on the other hand, loses quite a bit of temperature just during transport through the pipes. Ultimately, however, it depends on the heating system of a house. With a solar thermal system, for example, it is actually more energy-efficient to use hot water from the tap, according to the consumer advice center.
