Question About Frozen Pipes

When water pipes freeze and burst it is most likely the hot water pipes (I don’t have a cite for this and I could be wrong). My understanding as to why this is so is that the toilet acts as a pressure release for the cold water pipes. When cold water pipes freeze, the water in the pipes can be pushed out into the toilet tank so that the ice will expand along the length of the pipe, rather than expand outward and break the pipe.
If this is so, is there a faucet with a pressure release for the hot water? I would think that if such a device were installed in the sink furthest from the hot water heater it would greatly reduce the chances of burst pipes.

I don’t know where a story like that came from.
A toilet valve is a positive shut off valve.
A cold water tap is probably used much more than the hot tap and that will be triple at night.
I would say, if hot water pipes statistically freeze more often its because cold water is used more.

Kind of reminds me of the old myth that when a fire engine is running during a fire the truck can pull the water out of toilets. :smack:

water freezing would likely occur at cold spots and in layers, this would be local freezing and the idea of pressure relief would have no effect.

the toilet tank valve holds against lots of pressure otherwise your toilet would always be running.

I remembered this thread while reading this article about frozen pipes. According to the interviewed expert,

I don’t know if that’s true (there are a lot of old wives tales among plumbers) but I do not particularly want to test it, either.

Hot water freezes faster.

Also (from someone who lives in a cold climate and has had her pipes freeze more than once) leaving faucets running, if you have vulnerable pipes, really works. The standard advice is to leave the hot water faucets running with a pencil-lead sized stream whenever it gets risky-cold. That relieve the pressure in the entire system, so the pipes don’t freeze all the way through.

How it was described to me by the owner of a large plumbing company, anyway. And It’s worked, since even during the big ice storm where my house had no heat or electricity for six days, and icicles were coming out of every faucet…once it all thawed, no problem. I’d left all my faucets running as instructed.

No it doesn’t, at least not in any way that’s sufficiently reproduceable, and that article is full of speculative jibber jabber.

Cite to back up your claims, please?

I’ve heard the “hot water lines freeze faster” for decades and every time I’ve googled it I find it reinforced. This last winter even my local water department was advertising that folks let the HOT, not the cold, water trickle since the hot froze up faster. But I am neither a physicist nor a chemist so I can’t evaluate such claims.

But if you have a valid, understandable cite that claims cold water pipes actually freeze up faster than hot water pipes, and why I should ignore the advice of countless plumbing companies, municipalities, water departments and .edu sites, I am all ears, seriously. Since I live in a very cold-winter climate, and have a crawl space instead of a basement, I am personally invested in this.

Actually, that would violate the laws of physics.

Hot water molecules are more active than cold water molecules. That means that their motion would require greater energy to slow (and thus “cool”) them than would hot water. For an example of this, take a two pans of water, one boiling hot and one cool but still liquid, outside in subzero weather and throw them into the air.

While they will both freeze in mid-air, the cold water will likely be already frozen in the pan before you get a chance to throw it.

Again, cite? Look up the Mpemba effect.

I has cites. Thousands more where the below came from. Please provide cites to counter this. Otherwise you are a random person online with an opinion, which is amusing but not authoritative.

My neighbor and I TNR and feed a colony of feral cats. I’ve actually non-scientifically tested this theory by mixing up generic canned cat food with hot water and with cold water. For real, the canned food mixed with hot water freezes faster on extremely cold mornings. We mix canned food with cold water so it doesn’t freeze as quickly, because cats won’t eat frozen food.

Valid possible explanations :

  1. The hot water corrodes the inside of the pipes and causes wear more rapidly. I’m almost certain this is the reason : at my parent’s house, the same gauge of copper pipe was used for both the hot and cold sides of the system. The hot lines sprang dozens of leaks over time (apparently you are supposed to use a thicker gauge of copper for the hot side)

  2. The pressure relief theory caused by toilet valves might be valid.

It has absolutely nothing to do with “hot water freezes faster” because in water lines, the water is only hot when the circuit is in use (and it won’t freeze then). The rest of the time, the temperature in the hot line is the same as in the cold line.

The Mpemba effect is not consistent:

While under certain conditions IT could happen, it does not do so consistently. That lack of consistency makes it a speculative claim, not a scientific one.

Also, the effect has to do with water vapor dispersing into clouds of gas more easily if it is hotter. It has absolutely no effect on liquid water in a pipe.

It has nothing to do with relieving the pressure. Flowing water does not freeze. (OK it’ll freeze eventually, but it might take -80°C to get flowing water to freeze) If you leave a pencil-lead thin stream, the pipes may start to freeze, but eventually the opening would get small enough to make the water flow at sufficient speed to stop the complete freezing.

The Master Speaks

Perhaps it’s a case of “one size fits all” advice.

Here in NC, a lot of people have tankless water heaters, installed outside. Those people are advised to turn the hot water on at a trickle to avoid the pipes that are outside freezing. The pipes in the crawl space are at far less risk.

I was glad I installed my tankless in my crawlspace. I don’t quite understand why people put them outside, but no doubt there’s a practical reason. (Luckily, my “crawl space” is about 9’ high, where the tank is. It’s 4’ on the other side of the house.

I’m still thinking about the toilet-as-relief-valve theory.

For one thing, I can test the sensitivity of the float valve to pressure. I’d open the cold water faucet in the sink, and flush the toilet. When the toilet stops, turn off the cold water and see if the toilet valve opens for a moment. If so, then I’ve established that it’s sensitive to pressure (which I don’t have a hard time believing.)

The next question is whether that’s enough to do the trick.

First of all, pressurized water has to be COLDER to freeze. So, relieving the pressure won’t stop the freezing, it would exacerbate it. Second, once the water is frozen, the pressure relief would be just at one end, and not rapid (ice doesn’t flow very fast). So, would that really be enough?


i lived in a place without central heat, manual heater in center room. the bathroom was a the rear. went away for a winter weekend; bath OK, sink OK, toilet froze.

The two or three times my pipes froze and burst, it was the cold water pipes which fed outdoor spigots. I forgot to turn off the water and drain the pipes over the winter.

No shit!