# Hot water makes ice cubes freeze quicker? **URL:** \ **Category:** Factual Questions\ **Created:** [May 13, 2006, 5:48pm UTC](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662 "2006-05-13T17:48:34Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Quercus](https://avatars.discourse-cdn.com/v4/letter/q/7ab992/32.png) [@Quercus](https://boards.straightdope.com/u/Quercus)\ **Post date:** [May 15, 2006, 1:20pm UTC](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662/21 "2006-05-15T13:20:43Z")
> [@GiantRat](#): > > Not such a hot idea to use hot tap water, though. Hot water tends to contain higher concentrations of potentially dangerous minerals and elements that gather as sedimentation in your water heater. At least, that’s what a plumber friend told me when I commented about loving to drink shower water. There, I said it. I drink shower water. Just one question on this: if the ‘dangerous minerals and elements’ aren’t already in the tap water coming into the water heater, how do they get there? And if they are coming from the tap water, doesn’t the fact that there’s deposit in the heater mean there is on average less of them in the water leaving the heater than in the cold tap water coming in? I think this is right up there with ‘Hot water freezes faster’. It’s just possible that a poorly adjusted hot water heater could have some bacterial growth, but so rare that it’s not a general concern. And ‘dangerous elements’ aren’t going to be there any more than anywhere else. Guzzle away in the shower with no fear. ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [May 15, 2006, 1:26pm UTC](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662/22 "2006-05-15T13:26:47Z")
Ah, all you people with short memories. Mine goes back to the 40s and we had an old-fashioned fridge whose freezer compartment was large enough for two ice cube trays and a couple cans of frozen juice. More to the point, it was not auto-defrost and, especially in the humid summer the freezer compartment was usually heavily encrusted with ice. If you put a tray of hot water in the freezer, it melted down some of the encrustation and froze relatively quickly. There might also have been significant evaporation. A tray of cold water just sat on the ice and froze more slowly. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [May 15, 2006, 2:42pm UTC](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662/23 "2006-05-15T14:42:21Z")
Much has been written about this one and it’s interesting that despite an authoritative article from Cecil that it is still not settled. A Google search on “hot water freeze faster cold water” gives Cecil’s column as the second entry! [Here is the first entry](http://math.ucr.edu/home/baez/physics/General/hot_water.html), the best treatment of the subject that I’ve found. It is possible to create a situation where hot water will freeze faster but that is because of uncontrolled variables other than temperature. To those who have pointed out in other threads that the freezer compressor will run more often if a tray of hot water is in the freezer and therefore freeze it faster, I will add that the job of the compressor and thermostat is to keep the temperature of the freezer nearly constant, so this should not make any difference, unless the hot water overwhelms the compressor’s ability to cool the freezer, in which case the hot water would freeze more slowly. A better test would be to put two trays outdoors in cold temperatures on the same bare surface (to eliminate the “frost melt” effect). Time for another [entry](http://www.seigle.net/gqfaq.html#hot) in the Unofficial FAQs. ---
**Author:** ![Carnacki](https://avatars.discourse-cdn.com/v4/letter/c/b5e925/32.png) [@Carnacki](https://boards.straightdope.com/u/Carnacki)\ **Post date:** [May 15, 2006, 5:03pm UTC](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662/24 "2006-05-15T17:03:47Z")
The best explanation I’ve heard for this is the “Freezing momentum” explanation. Much like a ball rolling downhill which started on a higher, steeper hill can overtake a ball that started much lower, hot water as it freezes gains freezing momentum - so the water that started at 90 degrees will be cooling at a much faster rate once it hits, say, 30 degrees than will the water that started at 30. No cite, but it just kind of ‘feels right’, doesn’t it? ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [May 15, 2006, 5:31pm UTC](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662/25 "2006-05-15T17:31:04Z")
> [@KidScruffy](#): > > The best explanation I’ve heard for this is the “Freezing momentum” explanation. . . .No cite, but it just kind of ‘feels right’, doesn’t it? Sorry, no basis in fact. Rolling balls are governed by the force of gravity. A force on a mass results in an acceleration, which is not an analogy for heat loss. If you wanted to really stretch this analogy, you would have to place both balls on the same hill, not one on a steeper hill. And the hill would be a curve with steepness that levels off (my guess would be exponentially but I don’t know the formulas for heat loss to ambient air). Heat loss by convection (i.e., loss of heat by an object to calm air around it) is proportional to the difference in temperature between the object and the surrounding air. The hotter water will lose heat faster at first, but when it cools to the same temperature as the starting temperature of the cooler water, it will lose heat at the same rate as the cooler water started out. This assumes no evaporation from the hotter water, no differences in dissolved gasses or impurities, same container, etc. So the cooler water has a head start that the hotter water can never make up. There is no such thing as building momentum for heat loss–heat loss can be calculated at a point in time from the parameters at that time without knowing anything about the history of that object’s cooling process. [Here’s a cite.](http://hyperphysics.phy-astr.gsu.edu/HBASE/thermo/heatra.html) OTOH a Google search for “freezing momentum” came up with exactly one hit, a highly technical paper entitled, “Colour transparency and scaling properties of nuclear shadowing in deep inelastic scattering” of which I found even the abstract impenetrable but I can tell you they weren’t talking about how long it takes for hot water to freeze. ---
**Author:** ![Carnacki](https://avatars.discourse-cdn.com/v4/letter/c/b5e925/32.png) [@Carnacki](https://boards.straightdope.com/u/Carnacki)\ **Post date:** [May 15, 2006, 5:49pm UTC](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662/26 "2006-05-15T17:49:56Z")
> [@CookingWithGas](#): > > Sorry, no basis in fact. Ack, sorry **CookingWithGas** - I had to choose between being lambasted for joking in GQ, and looking like a dunce\*. I think I chose poorly - I don’t know much about science, though, so thanks for the informative reply. Sorry for side-tracking the OP. –KidScruffy - I have been known to repeat the ‘cooling momentum’ theory, and see who will fall for it. So in case you’re wondering who is helping spread the ignorance that the SD is fighting…guilty as charged. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [May 15, 2006, 6:26pm UTC](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662/27 "2006-05-15T18:26:42Z")
> [@KidScruffy](#): > > I had to choose between being lambasted for joking in GQ, and looking like a dunce\*. I think I chose poorly But which one did you choose? 😕 OK, I still don’t know which one of us got whooshed. 😃 Me 'cuz I missed the joke or you with a theory that doesn’t hold up. ---
**Author:** ![Carnacki](https://avatars.discourse-cdn.com/v4/letter/c/b5e925/32.png) [@Carnacki](https://boards.straightdope.com/u/Carnacki)\ **Post date:** [May 15, 2006, 6:57pm UTC](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662/28 "2006-05-15T18:57:55Z")
> [@CookingWithGas](#): > > But which one did you choose? 😕 > > OK, I still don’t know which one of us got whooshed. 😃 Me 'cuz I missed the joke or you with a theory that doesn’t hold up. It’s definitely a joke…sorry for the whoosh. 🙂 I was hoping the “it just sort of feels right” logic would give it away, but I guess I’m too little known here to not be taken seriously. Actually, now that I think about it, it’s probably easier for you to believe that I _did_ endorse that theory, and now I’m trying to talk my way out of it. So maybe the last laugh’s on me. 🙂 –KidScruffy ---
**Author:** ![BoringDad](https://avatars.discourse-cdn.com/v4/letter/b/ad7895/32.png) [@BoringDad](https://boards.straightdope.com/u/BoringDad)\ **Post date:** [May 15, 2006, 9:30pm UTC](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662/29 "2006-05-15T21:30:24Z")
> [@Musicat](#): > > Please propose a test where, given two samples of pure H[sub]2[/sub]O, at exactly the same temperature, you can tell which one was hotter a few minutes ago from merely testing the samples. I obviously did not make that claim. > [@](#): > > If “some of the water is very cold and some still very hot” then you don’t have a uniform sample and you have altered the question to “does hot water cool faster than cold water if non-uniform cooling or convection is allowed?” The OP was not so precise as to include or rule out such things, so the question was not altered. As I stated, the blanket statement “Hot water freezes faster” is generally false. But if you press it, it becomes a question of semantics, heat transfer, volume, odd shape, surrounding conditions, etc. ---
**Author:** ![BoringDad](https://avatars.discourse-cdn.com/v4/letter/b/ad7895/32.png) [@BoringDad](https://boards.straightdope.com/u/BoringDad)\ **Post date:** [May 15, 2006, 9:36pm UTC](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662/30 "2006-05-15T21:36:10Z")
> [@Musicat](#): > > Please propose a test where, given two samples of pure H[sub]2[/sub]O, at exactly the same temperature, you can tell which one was hotter a few minutes ago from merely testing the samples. I obviously did not make that claim. > [@](#): > > If “some of the water is very cold and some still very hot” then you don’t have a uniform sample and you have altered the question to “does hot water cool faster than cold water if non-uniform cooling or convection is allowed?” The OP was not so precise as to include or rule out such things, so the question was not altered. As I stated, the blanket statement “Hot water freezes faster” is generally false. But if you press it, it becomes a question of semantics, heat transfer, volume, odd shape, surrounding conditions, etc. ---
**Author:** ![daffyduck](https://avatars.discourse-cdn.com/v4/letter/d/ec9cab/32.png) [@daffyduck](https://boards.straightdope.com/u/daffyduck)\ **Post date:** [May 15, 2006, 11:24pm UTC](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662/31 "2006-05-15T23:24:11Z")
> [@CookingWithGas](#): > > To those who have pointed out in other threads that the freezer compressor will run more often if a tray of hot water is in the freezer and therefore freeze it faster, I will add that the job of the compressor and thermostat is to keep the temperature of the freezer nearly constant, so this should not make any difference, unless the hot water overwhelms the compressor’s ability to cool the freezer, in which case the hot water would freeze more slowly. You’re forgetting that when the compressor runs, it blows cold air around the freezer compartment which does a much better job of freezing the cubes than stagnant cold air does. I’ve observed this first hand as I make and consume a lot of ice. Putting trays into a running freezer makes ice much faster than putting them into a not running freezer, even though the temperature of the not running freezer is, by your own definition, colder than the temperature of the running freezer. I always make my ice from water stored in the cold section of the fridge, so the starting temp is always the same, but the time to cubes is much quicker on hot days when the compressor works more often to maintain the temp of the freezer. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [May 16, 2006, 4:59pm UTC](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662/32 "2006-05-16T16:59:48Z")
> [@daffyduck](#): > > You’re forgetting that when the compressor runs, it blows cold air around the freezer compartment which does a much better job of freezing the cubes than stagnant cold air does. This is true, and is how a convection oven works. As warm water cools, it is warming the air immediately around it. If that air is calm, a warm envelope is created around the water (neglecting for the moment convection currents). However, if the air is blowing around the warmer air is carried off, refreshing the area near the water. I did not consider the actual movement of the air, just the constant temperature. Regardless, if you use the “compressor runs more often” argument to prove that hotter water freezes faster, you have created another variable, unless you put both trays in at the same time. ---
**Author:** ![BoringDad](https://avatars.discourse-cdn.com/v4/letter/b/ad7895/32.png) [@BoringDad](https://boards.straightdope.com/u/BoringDad)\ **Post date:** [May 16, 2006, 5:40pm UTC](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662/33 "2006-05-16T17:40:44Z")
> [@CookingWithGas](#): > > Regardless, if you use the “compressor runs more often” argument to prove that hotter water freezes faster, you have created another variable, unless you put both trays in at the same time. Definitely true. And not only that, but a freezer does NOT maintain a constant temperatire, it maintains temp within a range of several degrees. So if you force the freezer on, the initial starting temp of the freezer will be several degrees lower than if you did not force the freezer on. Depending on the size of the freezer, the thermal mass in freezer, amount of water, etc the colder freezer conditions could carry through for the duration of the experiment. ---
**Author:** ![solkoe](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@solkoe](https://boards.straightdope.com/u/solkoe)\ **Post date:** [May 16, 2006, 6:18pm UTC](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662/34 "2006-05-16T18:18:16Z")
Has anyone considered how hockey ice rinks are cleaned between periods? I believe hot water is used. ---
**Author:** ![solkoe](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@solkoe](https://boards.straightdope.com/u/solkoe)\ **Post date:** [May 16, 2006, 6:21pm UTC](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662/35 "2006-05-16T18:21:55Z")
I should have added that I build a hockey rink in my backyard every year. I use hot water whenever possible. As stated above, there are a lot of variables in this. Certainly the size, shape of the container is a big factor. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [May 16, 2006, 6:49pm UTC](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662/36 "2006-05-16T18:49:50Z")
> [@solkoe](#): > > Has anyone considered how hockey ice rinks are cleaned between periods? I believe hot water is used. I believe so based on my observations of the steaming trail left behind the Zamboni. This may not be because it freezes faster, however. If it _does_ freeze faster it’s only because a bunch of it evaporates leaving a thinner layer to freeze. You could achieve the same effect by using less water to begin with. There may be some other benefit to using hot water to melt a little of the existing surface and allow it to refreeze, maybe makes for smoother ice or something, I dunno. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [May 16, 2006, 6:51pm UTC](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662/37 "2006-05-16T18:51:26Z")
> [@solkoe](#): > > I should have added that I build a hockey rink in my backyard every year. I use hot water whenever possible. > As stated above, there are a lot of variables in this. Certainly the size, shape of the container is a big factor. What are you saying? You use hot water because you think it freezes faster? I think that the problem may most simply be stated as, all other factors being equal - identical amounts of water, of the same composition, in identical containers, side by side under identical temperatures - the colder water will undoubtedly freeze first. ---
**Author:** ![Punoqllads](https://avatars.discourse-cdn.com/v4/letter/p/d2c977/32.png) [@Punoqllads](https://boards.straightdope.com/u/Punoqllads)\ **Post date:** [May 16, 2006, 10:58pm UTC](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662/38 "2006-05-16T22:58:00Z")
> [@CookingWithGas](#): > > Sorry, no basis in fact. …well… It seems reasonable to me to consider convection currents and temperature gradients the equivalents of the “cooling momentum” of a substance. ---
**Author:** ![Punoqllads](https://avatars.discourse-cdn.com/v4/letter/p/d2c977/32.png) [@Punoqllads](https://boards.straightdope.com/u/Punoqllads)\ **Post date:** [May 16, 2006, 11:06pm UTC](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662/39 "2006-05-16T23:06:30Z")
> [@Colibri](#): > > I think that the problem may most simply be stated as, all other factors being equal - identical amounts of water, of the same composition, in identical containers, side by side under identical temperatures - the colder water will undoubtedly freeze first. Sounds reasonable. However, I recommend that you read the article that **alterego** cited ([http://math.ucr.edu/home/baez/physics/General/hot\_water.html](http://math.ucr.edu/home/baez/physics/General/hot_water.html)) before deciding that “reasonable” equates to “truth”. Specifically, the parts (and references) that say that hot water can freeze faster than cold water even after taking into account any influences due to evaporation and dissolved gasses. ---
**Author:** ![lissener](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lissener/32/6139_2.png) [@lissener](https://boards.straightdope.com/u/lissener)\ **Post date:** [May 16, 2006, 11:44pm UTC](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662/40 "2006-05-16T23:44:43Z")
> [@CookingWithGas](#): > > There may be some other benefit to using hot water to melt a little of the existing surface and allow it to refreeze, maybe makes for smoother ice or something, I dunno. Exactly right. [Previous page](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662.md?page=1) [Next page](https://boards.straightdope.com/t/hot-water-makes-ice-cubes-freeze-quicker/356662.md?page=3)