Addressing The Divisive Topic That Is Boiling Water

April 2, 2026 by Maya Posch 10 Comments

The topic of boiling water is apparently a rather divisive topic, with plenty of strong opinions to go around on what is safe and the most efficient way to go about it. Thus in a new video [Cahn] sought to address the many comments that came in after his previous testing of electric kettles on either 12 VDC or 240 VAC.

What’s interesting about this whole topic is that at its core the overall efficiency of boiling water is simply a matter of calculating the energy input minus energy losses, with the remaining energy going into the water.

As we can see in the video, using a higher battery voltage doesn’t really change the efficiency of a 12 VDC kettle, but the higher current draw does manage to melt a fuse that can’t take the heat — requiring a 20 amp fuse instead of the 15 A one.

One change that does make a difference is how it’s connected. Replacing the thin gauge wiring and the attached cigarette lighter plug on the 12 VDC kettle with beefier cable and an Anderson plug made things run cooler, resulting in an efficiency bump of about 10%. This cut the time required to get the water boiling by around 6 minutes.

Added to this test were an induction hob and an iso-butane-powered Jetboil, both of which scored rather unimpressively. For the induction option it’s obvious that a lot of energy is wasted by having the pan radiate it away from the water, while burning iso-butane loses energy through the exhaust gases. Ultimately what you pick to boil water with should thus be mostly determined by convenience rather than sheer physics.

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Comparing The Power Usage Of 12 VDC And 240 VAC Kettles

March 26, 2026 by Maya Posch 40 Comments

If you have a 12 VDC power system, like the battery of a PV solar system or car, would it be more efficient to boil water for that cup of tea with that 12V straight from the battery, or use a 240 VAC mains kettle via a ~90% efficient inverter instead? That’s the question that [Cahn] decided to answer experimentally, using a bulky 3 kW inverter and a collection of electric kettles.

Although the used amount of 500 mL of water is boiled much faster in the 2,200 Watt mains kettle than in the 150 and 350 Watt low-voltage kettles, this obvious difference is somewhat irrelevant if you’re only concerned with efficiency. To measure the power used a Victron smart shunt was used with each run, keeping in mind that a perfect efficiency for heating 500 mL from room temperature to boiling is around 43-44 Wh.

With two runs per kettle, the 240 VAC kettle used 65-70 Wh. The first ‘150 Watt’ kettle pulled nearly 200 Watt to boil the water after about 20 minutes, using 62-64 Wh. The second ‘150 Watt’ kettle pulled around 180 Watt, took 23-25 minutes and used 68-74 Wh. Finally, the ‘350 Watt’ kettle drew over 420 Watt and used 50-56 Wh in just over 8 minutes.

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Using A Level 2 Charger To Work Around Slow 120 VAC Kettles

December 1, 2025 by Maya Posch 77 Comments

To those of us who live in the civilized lands where ~230 VAC mains is the norm and we can shove a cool 3.5 kW into an electric kettle without so much as a second thought, the mere idea of trying to boil water with 120 VAC and a tepid 1.5 kW brings back traumatic memories of trying to boil water with a 12 VDC kettle while out camping. Naturally, in a fit of nationalistic pride this leads certain North American people like that bloke over at the [Technology Connections] YouTube to insist that this is fine, as he tries to demonstrate how ridiculous 240 VAC kettles are by abusing a North American Level 2 car charger to power a UK-sourced kettle.

Ignoring for a moment that in Europe a ‘Level 1’ charger is already 230 VAC (±10%) and many of us charge EVs at home with three-phase ~440 VAC, this video is an interesting demonstration, both of how to abuse an EV car charger for other applications and how great having hot water for tea that much faster is.

Friendly tea-related transatlantic jabs aside, the socket adapter required to go from the car charger to the UK-style plug is a sight to behold. All which we starts as we learn that Leviton makes a UK-style outlet for US-style junction boxes, due to Gulf States using this combination. This is subsequently wired to the pins of the EV charger connector, after which the tests can commence.

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Charting The Efficiencies Of Boiling Water

June 2, 2012 by Brian Benchoff 32 Comments

Water takes a lot of energy to heat up. If you’d like evidence of this, simply jump into a 50° F swimming pool on Memorial Day. Despite the difficulty of heating water, that simple act accounts for a lot of industrial processes. From cooking a steak to running a nuclear reactor, there isn’t much that doesn’t involve heating water.

[Tom Murphy], Physics prof at UCSD decided to test out exactly how efficiently he could boil water. Armed with a gas stove, electric kettle, microwave, and a neat laser pointer/photodiode setup on his gas meter to measure consumption, he calculated exactly how much energy he was using to make a cup of tea.

The final numbers from [Tom]’s experiment revealed that a gas stove – using a pot with and without a lid on large and small burners – was about 20% efficient. A gas-powered hot water heater was much better at 55% efficiency, but the microwave and electric kettle had a miserable efficiencies of around 15 and 25%, respectively. There is a reason for the terrible inefficiency of using electricity to heat water; if only the power from the wall is considered, the electric kettle put 80% of energy consumed directly into the water. Because the electricity has to come from somewhere, usually a fossil-fueled power plant that operates at around 30% efficiency, the electric kettle method of turning dinosaurs into hot water is only about 25% efficient.

The take-home from this is there’s a lot of power being wasted every time you run a bath, make some coffee, or wash the dishes. We would all do better by decreasing how much energy we use, much like [Tom]’s efforts in using 5 times less power than his neighbor. Awesome job, [Tom].