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Freezing hot water pipes?


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#1 infamous

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Posted 11 February 2007 - 05:29 PM

I was watching the weather channel last night and the forecaster was talking about water pipes freezing. His comments detailed the fact that "Hot water pipes will freeze quicker than cold water pipes". I thought this information sounded a bit flawed but not knowing for sure, I thought I'd ask the membership here if anyone had any documented data on the subject. I find it rather hard to believe that the hot water pipe would freeze first. Any thoughts?......................................Infy

#2 Cedars

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Posted 11 February 2007 - 06:28 PM

I was watching the weather channel last night and the forecaster was talking about water pipes freezing. His comments detailed the fact that "Hot water pipes will freeze quicker than cold water pipes". I thought this information sounded a bit flawed but not knowing for sure, I thought I'd ask the membership here if anyone had any documented data on the subject. I find it rather hard to believe that the hot water pipe would freeze first. Any thoughts?......................................Infy


I dont think he is correct however I think he is refering to this:

Mpemba effect - Wikipedia, the free encyclopedia

In real life at the farm it was the cold water pipes we had trouble with freezing up. One method used was to allow a drip to continue thru the coldest nights. Once in a while the drain would freeze up dependent on wind direction. Moving water wont freeze up so easily.

#3 infamous

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Posted 11 February 2007 - 06:43 PM

I dont think he is correct however I think he is refering to this:

Mpemba effect - Wikipedia, the free encyclopedia

Thanks for the link Cedars, I guess I could have saved your time with this if I had just looked it up at Wiki. So, this is called the Mpemba effect, very interesting......................................Infy

#4 Jay-qu

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Posted 11 February 2007 - 06:51 PM

I had to admit defeat on this once at a party when one of my mates proclaimed that hot water freezes faster, I thought the idea was far fetched so 'to wiki' we went and alas I was wrong! (I try not to let that happen to often :D)

I did take some solace in the fact that it had to be previously boiled water for the Mpemba effect to work, not just warmer water :)

#5 infamous

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Posted 11 February 2007 - 07:14 PM


I did take some solace in the fact that it had to be previously boiled water for the Mpemba effect to work, not just warmer water :)

Yes, I believe it has something to do with the desolved gases in water which has been boiked, at least according to Wiki.

This is a little off topic, but then again, it is my thread, right?? Sooooo,


I was doing some experimenting with the expansion of water and noticed something else which I've never been able to get a good answer for. Using a small diameter tube sealed at the bottom, I filled it half full of water. Then holding it over a burner, I noticed a sharp decrease in the volume shortly before the water began to rise in the tube due to the expansion caused by it's heating. I've never been able to explain why this short contraction takes place slightly before expansion begins. I thought once that it might be the glass expanding first before the water because it sees the heat first, but the expansion of glass is so low and the thinness of the glass tube allows the water to begin heating almost instantly. This appears to be the only explanation but the rates of expansion for water and glass don't seem to add up to the experimental results........................thoughts?

...........................................Infy

#6 C1ay

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Posted 11 February 2007 - 09:35 PM

I was watching the weather channel last night and the forecaster was talking about water pipes freezing. His comments detailed the fact that "Hot water pipes will freeze quicker than cold water pipes".


I think your forecaster has fallen victim to some myth. I've also heard that hot water freezes faster in the ice tray. Not true. In reality there is really no such thing as cold as cold is only an absence of heat, i.e. you have some heat or you have more heat. To freeze hot water involves removing more heat than you would have to remove from water that already has less heat, cold water. Given two samples, one with some heat and one with more heat, and some common aparatus to remove heat from both it seems obvious that the one with less heat to begin with will win the race....

#7 CraigD

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Posted 11 February 2007 - 11:48 PM

I think your forecaster has fallen victim to some myth.

For most conditions, I agree. For the temperatures of typical residential cold and hot water – about 5° and 60° C – the colder water will freeze much faster than the hot.

For the Mpemba effect Cedars notes to be significant, several conditions must be met. The water must typically be between 60° and 90°, and must either be in an vessel that allows evaporation, or must contain significant dissolved minerals and be in a container that allows them to precipitate out of it.

I suspect, but have never experimentally tested (I don’t have a thermometer that’s easy to put inside a copper pipe) that, under very specific conditions, hot water pipes might freeze before cold water pipes. When both pipes have flowing water – not unusual, as many people slightly open faucets to cause a slight flow in exposed pipes to prevent them from freezing. The inside of the cold pipe may form a thin layer of ice that insulates it, preventing the slowly flowing water from freezing. The inside of the hot pipe may not form this layer, causing it to conduct heat out of the water more quickly, cooling and freezing the water. This scenario is more likely if one opens only a cold water faucet, assuming that the exposed hot water pipes don’t need water flow to avoid freezing.

Of course, if a particular building’s hot water pipes are more exposed than its cold water pipes, they’ll be more prone to freezing, but this isn’t an example of counterintuitive physics, just strange plumbing.

I've also heard that hot water freezes faster in the ice tray. Not true.

I’ve actually timed 65° (hot) water and 85° (very hot) water in ordinary plastic ice cube trays in an ordinary freezer, and confirmed published experimental results showing that the 85° water froze in less than half the time of the 65° water, as well as that the 85° water formed noticeably smaller ice cubes than the 65° water.

Can hot water freeze faster than cold water?” has a good discussion of the strange freezing conditions.

This is good material for home experimentation, requiring nothing not found in the typical kitchen, other than a good thermometer.

#8 Jay-qu

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Posted 12 February 2007 - 03:57 AM

Sorry Im not sure I know what you are proposing, do you mean to say that the slight contraction is due to the gases been removed or due to hydrogen bonds been broken down?

#9 CraigD

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Posted 12 February 2007 - 06:10 AM

do you mean to say that the slight contraction [of ice cubes made from initial hotter water] is due to the gases been removed or due to hydrogen bonds been broken down?

As I understand from the explanations of less amateurish scientists, it’s due mostly to an actual loss in whole water molecules due to increased evaporation.

Note that the rate of heat transfer out of water in an ice cube tray is proportional to its surface area, while the amount of heat that must be transferred is proportional to its volume, and that, in the typical ice cube tray, surface area changes very little as volume is reduced.

As I understand it, this reduction in water volume due to greater evaporation accounts for the 65° vs. 85° hot-water-freezing-faster-than-cold effect I witnessed in my freezer, but in other experimental setups, other effects could be dominant.

#10 Jay-qu

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Posted 12 February 2007 - 06:24 AM

sorry craig, that was in reply to infy's #5 :turtle:

#11 infamous

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Posted 12 February 2007 - 08:39 AM

Sorry Im not sure I know what you are proposing, do you mean to say that the slight contraction is due to the gases been removed or due to hydrogen bonds been broken down?

Actually Jay... I'm not proposing a theory because I have none. I was asking you fellows if there was any explanation for this effect and if anyone has any additional information about it. I personally have no idea why the short contraction occurs at the outset of heating. It seems to be just another curious feature about the character of water. Probably shouldn't have brought it up in this thread anyway, it seems to be causing some confusion. For the time being, maybe we should put that question on the back burner and finish our discussion on the freezing proporties of water. Sorry for the confusion gentlemen, my bad.

..............................................Infy

#12 CraigD

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Posted 12 February 2007 - 10:10 AM

Using a small diameter tube sealed at the bottom, I filled it half full of water. Then holding it over a burner, I noticed a sharp decrease in the volume shortly before the water began to rise in the tube due to the expansion caused by it's heating. ... I thought once that it might be the glass expanding first before the water because it sees the heat first, but the expansion of glass is so low and the thinness of the glass tube allows the water to begin heating almost instantly. This appears to be the only explanation but the rates of expansion for water and glass don't seem to add up to the experimental results.

Unless the water contains a lot of dissolved gas or particles that could volatilize or precipitate quickly, your glass expansion hypothesis is all that makes sense to me.

Are you able to capture images of the tube and water as it does this odd thing? Ideally high-speed, and high-resolution/magnification? All I can think to do is try to get as detailed as possible a look at what’s happening. (Having watched Mythbusters this weekend, I’m suffering from acute camera envy :yawn:)

#13 infamous

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Posted 12 February 2007 - 11:34 AM

Unless the water contains a lot of dissolved gas or particles that could volatilize or precipitate quickly, your glass expansion hypothesis is all that makes sense to me.

Are you able to capture images of the tube and water as it does this odd thing? Ideally high-speed, and high-resolution/magnification? All I can think to do is try to get as detailed as possible a look at what’s happening. (Having watched Mythbusters this weekend, I’m suffering from acute camera envy :yawn:)

I don't have access to the neccessary equipment so I'll have put those very good suggestions on hold CraigD. BTW, I'm a huge fan of Mythbusters myself..........................enjoy..............Infy

#14 Cedars

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Posted 12 February 2007 - 02:55 PM

I’ve actually timed 65° (hot) water and 85° (very hot) water in ordinary plastic ice cube trays in an ordinary freezer, and confirmed published experimental results showing that the 85° water froze in less than half the time of the 65° water, as well as that the 85° water formed noticeably smaller ice cubes than the 65° water.


A LONG time ago I experimented a bit with this. All I did was the hot tap water (letting it run for a while to get it as hot as I could) and the cold tap water (also letting it run for a while). It was well water.

Being easily distracted I was never attentive enough to time the freezing but the hot water ice cubes were significantly smaller than the cold water ones. I saw no point in using hot water for ice cubes even if it had the potential to freeze faster. Smaller ice cubes melt faster in your drink.

#15 Cedars

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Posted 12 February 2007 - 03:03 PM

I personally have no idea why the short contraction occurs at the outset of heating. It seems to be just another curious feature about the character of water.
..............................................Infy


I wonder if there would be a difference in the reaction using different types of water, such as Distilled vs treated tap vs untreated well vs RO.

#16 gribbon

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Posted 12 February 2007 - 03:59 PM

I think it's most likely to be becuase of how hot water has had the gas driven out of it, allowing it to freeze at a slightly lower temperature...

The Mpemba Effect: Hot Water Freezes before Cold - Succeed in Physical Science

Convection currents allow water to cool quicker when it is warm as well....

But the trouble is, is that bigger (more insulating) crystals are formed by slower cooling, and so if a pipe was fulll of cold water, it would develop only a thin layer of frost on the inside meaning it would still be allowed to cool relatively quick, but if the pipe had warm water in it, then it would develop large crystals on the inside, which would prevent it from cooling any more....:) :confused:

I'm confused...

On the other hand, here's a useful link which explains the effects of solutes in more detail...

Why water freezes faster after heating

Basically, Magnesium Carbonate in the water causes the freezing temperature to drop, but when water has been pre-heated, these just form a thin scale, which has little effect.

So that bit seems clear to me....:) ;) But what about limestone in the water?

Furthermore, if there is a fair amount of Carbon Dioxide in the water the limestone will react with it the produce soluble calcium bicarbonate? That can happen, but I'm not sure how much Carbon Dioxide normal water contains, and how much is realistically needed for this to happen...

CaCO3 + CO2 + H2O → Ca(HCO3)2

Calcium carbonate - Wikipedia, the free encyclopedia