Hot water line freezing in a friends home

cscaretaker

I have a friend of with an attached home. Their kitchen hot water line has frozen on them. The wall that the sinks is on faces the neighbors home and there's no insulation. I haven't been by their home but they have been keeping their cold water on at night during the freezing temps to keep the line from freezing but I never heard of a hot water line freeze. Especially since it's just their sink line. Any thoughts?

STEVEusaPA

Hot water freezes faster than cold water. Ever see the goofy news reporter every year throw hot water in the air and it freezes before hitting the ground? They never use cold water.
If the hot water sits, it will freeze. Either insulate the pipes, get some heat under the sink (or heat tape), or do the slow drip.

cscaretaker

Thanks! Never heard of heat tape. is that the wrap with the wire that plugs in and keeps the pipes warm?

If the water freezing a floor up from the basement in a vertical pipe, does the water usually sit that high? or would it be sitting lower in the line?

Jamie Hall

The pipes are always full, right up to the faucet, unless you deliberately drain them. And yes, hot water pipes can and do freeze. So, for that matter, do hot water heating pipes...

cscaretaker

Jamie Hall said:

The pipes are always full, right up to the faucet, unless you deliberately drain them. And yes, hot water pipes can and do freeze. So, for that matter, do hot water heating pipes...

wow. had no idea. I have to look into hot water heating pipes.

gramec9989

Under no circumstances should any water tubing be installed in an exterior wall or un-heated space, especially attics. Water lines at exterior walls should come up through the floor to supply toilets and into cabinets, not up in the wall.
Hot water freezes first because it is more dense because the free oxygen has depleted. Insulation will NOT prevent freezing, it will only slow the process.
If ambient temperatures are very low, open all cabinets to allow room heat to enter and help prevent freezing.
Close and insulate foundation vents to prevent frigid air from entering; ground heat and heat coming through the floors will keep crawlspaces around fifty degrees or so.
Eliminate all entry points where frigid air can enter.
Follow these guidelines and your pipes cannot freeze.

P.S. Call a real plumber, someone who understands these dynamics, to check your home and find which water lines are at risk, and make a plan to change things up if need be.

Leonard

Given typical 4 inch walls you likely can't get enough insulation between pipe and outside wall to keep pipe above freezing temp. ( Room side drywall adds some minor insulation so pipe will be colder than inside temps. Even worse if pipe is buried in middle of the insulation (kinda analogous to using 2 resistors as a voltage divider)

That's why you typically don't put pipes in outside walls. I suppose you could do it if wall was thick to add enough inches of insulation between pipe and outside and none between pipe and inside wall (but that's for new construction and thick walls. maybe 6-8 inchs thick, I haven't run the numbers)

ratio

gramec9989 said:

Hot water freezes first because it is more dense because the free oxygen has depleted.

Finally, a reason along with the assertion!

I'll have to think about this a while. Always before, I'd maintain that hot water won't freeze before cold, although it would loose more heat until the temperatures matched, at which point it would cool at the same rate. Barring the pathological case, they would freeze at the same time. I hadn't considered the (common) case of adulterated water.

Larry Weingarten

Hello, My understanding of the concept that hot water freezes first comes from the specific circumstance of putting cold water into an ice tray and then putting this into a frosty freezer, vs doing the same thing with hot water. The hot water melts the frost, greatly increasing the area of contact between freezer and ice tray. This is how hot water can lose heat faster than cold water and freeze sooner. I don't understand how hot water can be denser than cold, but am quite willing to learn!

Yours, Larry

mikeg2015

I believe there was also the concept of thermal momentum. It may relate to mini convection currents within the container.

hot_rod

Larry Weingarten said:

Hello, My understanding of the concept that hot water freezes first comes from the specific circumstance of putting cold water into an ice tray and then putting this into a frosty freezer, vs doing the same thing with hot water. The hot water melts the frost, greatly increasing the area of contact between freezer and ice tray. This is how hot water can lose heat faster than cold water and freeze sooner. I don't understand how hot water can be denser than cold, but am quite willing to learn!

Yours, Larry

I'm pretty sure cold water would be denser than hot.

Plenty of opinions on hot vs cold water freezing.

https://www.scientificamerican.com/article/is-it-true-that-hot-water/

Gsmith

Hot water is NOT denser than cold water, look it up! Water is most dense at about 39 deg F, it gets less dense as it gets hotter, and it gets less dense as it gets colder approaching freezing. When frozen it is about 10% less dense than liquid water, that's why ice floats. Think about Kurt Vonnegut's crazy world of ice 9, in which ice sinks, not floats.

SeymourCates

@hot rod

All of those cases where hot water was observed to freeze faster depend on an open surface and the interaction between the surface and the cold atmosphere surrounding the surface. Additional variables of entrained air and the type of container leave room for consideration of the possibility.

However, be assured that inside a pipe, which is what we are considering in the OP's situation, there is absolutely no chance that the hot water pipe will freeze before the cold water pipe and any suggestion of same is erroneous.

The most likely scenario for the OP is the fact that there is no effective difference between the hot and cold supplies once a period of approximately two hours has elapsed since the last HW draw. Both will freeze at the exact same time if subjected to the exact same ambient.

hot_rod

SeymourCates said:

@hot rod

All of those cases where hot water was observed to freeze faster depend on an open surface and the interaction between the surface and the cold atmosphere surrounding the surface. Additional variables of entrained air and the type of container leave room for consideration of the possibility.

However, be assured that inside a pipe, which is what we are considering in the OP's situation, there is absolutely no chance that the hot water pipe will freeze before the cold water pipe and any suggestion of same is erroneous.

The most likely scenario for the OP is the fact that there is no effective difference between the hot and cold supplies once a period of approximately two hours has elapsed since the last HW draw. Both will freeze at the exact same time if subjected to the exact same ambient.

I tend to agree, look at it from a heat transfer BTU to BTU transfer.

We all agree that you cannot make things cold, you remove heat energy. Stick your hand behind or below a running refrigerator to experience heat removal.

mikeg2015

More dissolved oxygen and minerals in cold water may make it have a slightly higher freezing point. In terms of when it fre see a 0.05f difference could be an hour. Not hard prod on that.

BobC

I live in a old house in a cold climate. I bought this house about 36 years ago and a few years after I tore the kitchen apart, The pipes to the upstairs bath went up the outside wall on the west side of the house and there was no easy way to run them up an inside wall. The pipes for the kitchen sink ran up an outside wall also.

I insulated all the outside walls but I put 2" thick shims between the water pipes and the outside and insulated the area between the pipes and the outside walls. There is no insulation between the pipes and the sheetrock. One bonus is the steam pipe for the bath goes up that same bay. When I installed the new sink I ran the kitchen pipes straight down through the floor, I did not leave them in that outside wall.

That bay with the bathroom pipes is open to the cellar (low 50's) and in the 30+ years I've never had a problem with freezing pipes. That steam pipe does a good job of keeping that bay above freezing. We see temperatures below zero every year around here and some who have switched from steam to FHW have freezing issues when it gets real cold.

This has worked well for me but your mileage may vary.

Bob

jumper

My experiences are that hot water line freezes sooner. Can't understand why.Mikeg2015's explanation makes sense but how significant can a little extra impurity be?

Even a little insulation helps,like burlap between pipe and masonry wall. Also just keeping under sink cupboards makes a big difference.

scrook_2

The hot water line, if off, will cool to ambient temperature, just as the cold will warm or cool to ambient, and like the cold line if that’s below 32F, will then freeze. Leave both at a dribble or more if required, not just the cold water, to prevent freezing in extreme weather. Add insulation if you can, and heat trace/tape it if you have to.

HomerJSmith

It is amazing how myths about how hot water freezes faster than cold water got entrenched in the plumbing industry. Hey, boiling water freezes faster than hot water. hahaha.

I say prove it.

HomerJSmith

Ever hear of supercool water, Mikeg2015? Supercool water "is the process of lowering the temperature of a liquid or a gas below its freezing point without it becoming a solid."

Drop a nucleus into a glass of supercool water and it will crystalize (freeze) instantly. Domestic water has plenty of nuclei called minerals. You can't supercool water that's full of nuclei.
Snowflakes form on a nucleus, like dust and don't form without them.
So, mineralized water should freeze faster than pure water.

That's my understanding.