# Cost of boiling water **URL:** \ **Category:** Factual Questions\ **Created:** [May 20, 2023, 10:17am UTC](https://boards.straightdope.com/t/cost-of-boiling-water/984321 "2023-05-20T10:17:46Z")\ **Posts on this page:** 9\ **Page:** 5
**Author:** ![Limmin](https://avatars.discourse-cdn.com/v4/letter/l/f04885/32.png) [@Limmin](https://boards.straightdope.com/u/Limmin)\ **Post date:** [May 26, 2023, 4:44pm UTC](https://boards.straightdope.com/t/cost-of-boiling-water/984321/81 "2023-05-26T16:44:02Z")
I take advantage of this effect when warming cold leftover food from the fridge. I sprinkle some water on top, which “catches” and spreads the heat, not to mention re-hydrating the food slightly. While heating, this added water boils off. ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [May 26, 2023, 5:47pm UTC](https://boards.straightdope.com/t/cost-of-boiling-water/984321/82 "2023-05-26T17:47:29Z")
> [@echoreply](#): > > I think you’ve missed a couple of decimal points, though, as that should be 0.0652kWh, which means £0.02 per day, not £0.20 per day and £7.43 per year. An easy mistake, and one I always assume I’ll make. (6.52kWh is enough energy to drive my car 25 miles!) Agggh! Converting all these foreign units boggles my brain. Why don’t you lot use sensible… Oops, sorry - that’s another thread altogether. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [May 26, 2023, 5:56pm UTC](https://boards.straightdope.com/t/cost-of-boiling-water/984321/83 "2023-05-26T17:56:12Z")
Freedom units! The world needs to learn them! /s ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [May 26, 2023, 7:15pm UTC](https://boards.straightdope.com/t/cost-of-boiling-water/984321/84 "2023-05-26T19:15:24Z")
> [@echoreply](#): > > Ending power usage was 0.06kWh. Perfect efficiency would have been 0.053 kWh. Assuming your meter is like mine, the granularity is 0.01 kWh, but I assume it ticks over a new number when the use is _at least_ that much. So, 88% efficiency or perhaps a bit less. > [@Mangetout](#): > > I’d expect higher efficiency than that, since making heat is usually the way energy gets wasted, but with a kettle, making heat is the exact purpose of the thing. Agreed; I was thinking of 80% as something of a lower bound. We’ll have lower efficiency here in the colonies due to the lower voltage. It takes longer to boil since it’s around half the power, which means more time for losses to manifest. > [@Limmin](#): > > Where did all that waste heat go? Like others said, it gets exhausted as hot air. The loud part of a microwave is just the cooling fan. They’d be a lot quieter if it weren’t for that. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 27, 2023, 1:30am UTC](https://boards.straightdope.com/t/cost-of-boiling-water/984321/85 "2023-05-27T01:30:06Z")
> [@Machine\_Elf](#): > > Thermal runaway is a major cause of uneven defrosting: Yeah, this is why I mentioned upthread (at least, I think it was this thread) that a microwave is the absolute worst possible tool for defrosting, even though everyone insists on using it for that purpose. ---
**Author:** ![Kedikat](https://avatars.discourse-cdn.com/v4/letter/k/ed655f/32.png) [@Kedikat](https://boards.straightdope.com/u/Kedikat)\ **Post date:** [May 27, 2023, 3:28am UTC](https://boards.straightdope.com/t/cost-of-boiling-water/984321/86 "2023-05-27T03:28:11Z")
Coming in late, I apologize if I am repeating. I personally use an electric kettle. It has a flat bottom inside. I feel this is a little less efficient than ones with the heating coil fully exposed directly to the water. It has an automatic shutoff. But this does not shutoff until the water has been boiling for quite some time. So I try to manually override it when I am in attendance. I shut it off as soon as bubbling starts. I feel that if bubbling has started, most of the water is probably fully as close to boiling as required. So I have quite a bit of control over the process if I choose to apply it. The fluid is in very direct contact to the heat input. In a microwave the situation is less direct in many ways. The smaller the volume/container of fluid that is in a microwave, the less energy is directed into it. Microwave ovens are designed to spread the energy as evenly about the interior as possible. There are a lot of hot/cold spots. The better ones try to even it out, but that also means energy spread across a possibly unused area. Energy that bounces about not absorbed and dissipated wasted. Also, the microwave is difficult to see directly, the state of the fluid. Or hear it. Boiling on a stove top seems so obviously the worst. Even an induction stove top. I think the most effective is a kettle with the heating coil directly exposed to the fluid. Paying attention to the bubbling. ---
**Author:** ![puzzlegal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/puzzlegal/32/3827_2.png) [@puzzlegal](https://boards.straightdope.com/u/puzzlegal)\ **Post date:** [May 27, 2023, 7:15am UTC](https://boards.straightdope.com/t/cost-of-boiling-water/984321/87 "2023-05-27T07:15:09Z")
> [@Whack-a-Mole](#): > > I have tried that and it seems to take a lot longer than a day for meat to completely thaw in my fridge (which is close to your temperature…give or take a degree or two). > > Which is fine…but the pound of ground beef I put in the fridge before bed is definitely not thawed by dinner time the next day. Not even particularly close. > > Maybe physics is different in my fridge. Same. It takes a couple of days for thin things to defrost, and longer for a bulky item, like a frozen chicken. I mostly defrost stuff by dunking it in a pot of water, and replacing the water from time to time. If i planned really well, i might defrost in the fridge. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [May 27, 2023, 1:09pm UTC](https://boards.straightdope.com/t/cost-of-boiling-water/984321/88 "2023-05-27T13:09:42Z")
> [@Kedikat](#): > > I personally use an electric kettle. It has a flat bottom inside. I feel this is a little less efficient than ones with the heating coil fully exposed directly to the water. It has an automatic shutoff. But this does not shutoff until the water has been boiling for quite some time. So I try to manually override it when I am in attendance. I shut it off as soon as bubbling starts. I feel that if bubbling has started, most of the water is probably fully as close to boiling as required. Economy-class kettles have a hand-operated switch to turn them on which automatically turns off shortly after the water has come to a full rolling boil - and then the switch never comes on again, which is inconvenient if you happen to want another cup of tea a few hours later. If the primary goal is to save money, this is fine. If you’re looking to burn money, Japan makes some more deluxe models, like this one: [https://www.amazon.com/gp/product/B01CEK4NHE](https://www.amazon.com/gp/product/B01CEK4NHE) It’s got a thermostat, so it can maintain water temperature indefinitely. You can also select different temperatures (160F, 180F, 190F, 208F) depending on what you need the water for. And then there’s a 6-hour delay timer, handy for suppressing the heating function until close to your wake-up time. It’s also insulated (or at least double-walled), so heat losses are pretty low. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 27, 2023, 1:18pm UTC](https://boards.straightdope.com/t/cost-of-boiling-water/984321/89 "2023-05-27T13:18:40Z")
> [@Machine\_Elf](#): > > Economy-class kettles have a hand-operated switch to turn them on which automatically turns off shortly after the water has come to a full rolling boil - and then the switch never comes on again, which is inconvenient if you happen to want another cup of tea a few hours later. If the primary goal is to save money, this is fine. If it’s well-insulated, then even after a few hours, it’ll still be fairly close to boiling temperature, and will only need to be turned back on for a very short time to get it back to a full boil. [Previous page](https://boards.straightdope.com/t/cost-of-boiling-water/984321.md?page=4)