Ask Pablo: kettle, range or microwave? – Tree hugger


Dear Pablo, what is most efficient for boiling water, a kettle, a saucepan on a stove or a microwave?

Whether you’re making tea or making pasta, knowing which of these three options is the most efficient way to boil water can help you become a better tree keeper and even save some money. Through some quick measurements and calculations, I hope to give a final answer to this question.

A large mug is roughly 350 ml, so I’ll be using 350 ml of room temperature (17 ° C) water. I’ll be using a Black & Decker kettle, a General Electric electric range with a Circulon 2L pot, and a 900W microwave with a turntable. Each individual’s power consumption is measured with a kill-a-watt meter until the water reaches boiling point or 100 ° C.

The water heater

Electric kettles are designed for efficiency and many of them have names like Eco Kettle. With kettles, the water is in direct contact with the heating element, there is no pot to heat, and most kettles have an integrated lid. The kettle had an average output of 1200 watts and took 125 seconds to boil the water, which corresponds to a power consumption of 0.04 kilowatt hours (kWh). I removed the cobwebs from the thermodynamic part of my brain and calculated that the theoretical energy required to heat 350 ml of water by 83 ° C in 125 seconds is 972 watts. If we divide this by the power actually used, we get an overall boiling water efficiency of 81% in a kettle.

The stove

The problem with an oven is twofold; The heat must be transferred from the element to the pot, and then the pot must warm up before this energy is given off to the water. If you don’t use a lid, there is a third cause of inefficiency in heat loss due to convection. The 6-inch elements of my stove use 1250 watts, and it took 318 seconds to boil 350 ml of water and used 0.11 kWh, almost four times the kettle. The theoretical energy required to heat 350 ml of water by 83 ° C in 318 seconds is 382 watts, which corresponds to an overall efficiency of only 30.5%. It is already clear that a kettle is far more efficient than the stove, more than twice as efficient. The next time you boil water to boil pasta, you can first heat the water in the kettle and then add it to your saucepan.

The microwave oven

Since the water heated by the microwave is contained in the mug, we not only heat the water, but also the mug to a certain extent. This increases the time and energy it takes to bring the water to a boil, but it also helps keep the water hot longer than boiling water that is poured into a mug at room temperature. Although it is a 900 watt microwave oven, the actual power consumption was 1350 watts. The 900 watts are most likely related to the power of the microwave emitter itself, which indicates an efficiency of 67% just to generate the microwaves. Boiling the same amount of water took 191 seconds and consumed 0.07 kWh. Using the same calculations as before, I found that the actual boiling water efficiency in the microwave oven is 47%, better than the stove, but still not as good as the kettle.

The bottom line

The clear winner is the kettle with 81% efficiency, followed by the microwave with 47% efficiency, with the stove being the Hummer H2 of the bundle with 30.5% efficiency. Assuming you currently use the stove to boil water, switching to a kettle for your morning tea will reduce daily electricity consumption from 0.11 kWh to 0.04 kWh. Over the course of a year, these daily savings add up from 0.07 kWh to 25.5 kWh. You could potentially save between $ 2.50 and $ 5.00 per year depending on where you live. Of course, most of us boil more water than just to make tea. If you add these savings up to every time you cook soup, pasta, homemade beer, or a lobster, it can add up.

Additional considerations when boiling water

Regardless of your method of boiling water, you can ensure maximum efficiency by boiling only what you need. Use your mug to measure the right amount or get yourself an eco kettle. If you’re in an office you might think that filling the kettle to the brim is most efficient, but think again. If the water is not used right away, much of the energy will go into the air, where your HVAC system must remove it. In addition, heating small amounts of water is faster than heating a large amount anyway.

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