Freezing Water Pipes: Hot or Cold is the Bigger Risk?

[gmax137]

Well, it's that time of year again in New England and discussions are on about freezing water pipes. I'm being told hot water pipes freeze and burst more often than the cold water pipes. Any believers ?

 

[phinds]

Well, it's that time of year again in New England and discussions are on about freezing water pipes. I'm being told hot water pipes freeze and burst more often than the cold water pipes. Any believers ?

I don't think so. My cold water pipe in a VERY badly insulated kitchen froze this morning, as it has one or two other times in the past 20 years. My hot water pipes have never frozen.

 

[DrStupid]

Any believers?

Any statistics?

 

[NukeProf]

There is no physical basis for that conclusion. It must be anecdotal and would never stand up to a controlled experimental investigation.

 

[russ_watters]

Oy. This sounds like an urban myth offshoot of the mostly mythical Mpemba effect:
https://www.physicsforums.com/threa...-tray-freeze-quicker-than-one-at-33-f.205920/

 

[1oldman2]

There is no physical basis for that conclusion. It must be anecdotal and would never stand up to a controlled experimental investigation.

As far as I understand things your correct, I remember that water freezing story from way back. I believe that it comes from the practice of leaving your cold water tap dripping which in turn makes the line far less likely to freeze, very few people however leave the hot tap dripping.

 

[cosmicthinker]

When the exhaust damper control switch fails closed on your hot water boiler, the gas line solenoid loses power and in failsafe mode shuts off the flow of fuel - then the reliable gas flame goes out, the water cools sufficiently to freeze on exceptionally cold days which in turn then ruptures all the heating zone hot water lines in every room of your home. It sounds like a Rube Goldberg, but there are instances where hot water pipes can and do freeze rather quickly. It is very expensive, BTW, to replace all those floors and ceilings.

 

[gleem]

@cosmicthinker. First post!

Were you just waiting in the wings waiting for an opportunity to make your debut?

OOPs forgot my manners. Welcome to Physics Forunm

 

[cosmicthinker]

@cosmicthinker. First post!

Were you just waiting in the wings waiting for an opportunity to make your debut?

Ha. Well, I've been reading these forum posts for years and have always enjoyed the discourse. Physics, mathematics and engineering have been my passion for 50 years. It is a first post for sure. The topic seemed so apt in reminding me of a personal disaster, I couldn't help myself. You might be surprised that there is a huge silent majority who visit and devour these entertaining conversations regardless of the level of complexity.

 

[1oldman2]

instances where hot water pipes can and do freeze rather quickly.

I had a similar "disaster" when a wind storm blew out the pilot light on my furnace while everyone was away,over two weeks in freezing weather. I can relate when you mention the damage. In this case both hot and cold lines broke so who knows which went first. I am hoping someone can join in with a "physics explanation" of the mechanics of how hot water would freeze before water of a lower temperature.

You might be surprised that there is a huge silent majority who visit and devour these entertaining conversations regardless of the level of complexity.

I couldn't agree more with that statement.

 

[russ_watters]

I am hoping someone can join in with a "physics explanation" of the mechanics of how hot water would freeze before water of a lower temperature.

All else being equal, it cannot.

 

[mrspeedybob]

Just an idea...

Heat accelerates dissolution and corrosion, so, if they are made of the same material, I would expect hot water pipes to have a shorter service life then cold water pipes.

If you live in a climate where freezing is going to be stress that stretches the pipe to the point of failure, I would expect old hot water pipes to fail while the matching cold water pipes were still strong enough to contain the pressure of freezing.

 

[1oldman2]

If you live in a climate where freezing is going to be stress that stretches the pipe to the point of failure, I would expect old hot water pipes to fail while the matching cold water pipes were still strong enough to contain the pressure of freezing.

Hi, my personal experience with freezing pipes after living in Montana (not the tropical part) Is that with the exception of the "PEX" style of waterline once the water reaches freezing no matter what condition the lines, they are going to break. The cost of PEX waterline may be a little high but compared to water damage its cheap insurance, no more PVC or copper lines for me if I can help it.

 

[cosmicthinker]

I would expect old hot water pipes to fail while the matching cold water pipes were still strong enough to contain the pressure of freezing.

Good forward thinking. This is exactly what happened. All of the old hot water zone pipes fractured, mostly at the many solder joints - 12 solder joints in one such room led to all 12 failing, so the resultant flooding was well distributed as was the resulting interior damage. I could give a good explanation why, but will yield to someone else who hasn't contributed his/her two cents. BTW, the cold water lines froze too, but none ruptured.

 

[cosmicthinker]

with the exception of the "PEX" style of waterline once the water reaches freezing no matter what condition the lines, they are going to break.

I use PEX lines extensively in my business. We shut down for the winter (including all heating) because we own and run a boat marina. We drain the water lines too. It occasionally gets exceptionally cold in Great Lake country and nearly everything, including inland bays that empty into the big lake freeze (not the Great Lake) to more than 2 ft (the ice fishermen love it)! Now PEX doesn't have good heat transfer properties and I don't know if hot water would slowly diffuse away the plasticizer and make it brittle, but just think of a flexible material (equipped with flexible heat radiation vanes) that might substitute for copper vaned lines and be less expensive. They would be exceptionally simple to install and might even outlast copper. Such an invention, if widely adopted, could reap millions! As an old Chemical Engineer and research scientist, I will give this some further thought...

 

[1oldman2]

All else being equal, it cannot.

Thanks Russ, I enjoyed reading the Mpemba link and it pretty well confirms what I was told 50 years ago. Hot water doesn't freeze faster than cold although there are a lot off variables when materials and installation are factored in.
Since the OP's (and my) question is answered I'm going to "bug out" of this thread before it degenerates into a case of two "good ol' " boys BSing around a wood stove and pizzing on each others boots.