"It all depends on how fast the cooling occurs, and it turns out that hot water will not freeze before cold water but will freeze before lukewarm water. Water at 100 degrees C, for example, will freeze before water warmer than 60 degrees C but not before water cooler than 60 degrees C.
A more mundane explanation is that hot water evaporates faster than cold, decreasing its volume and thus the time it takes to freeze. Cold water also could contain more dissolved gases, which lower its freezing point.
In short, hot water does freeze sooner than cold water under a wide range of circumstances. It is not impossible, and has been seen to occur in a number of experiments. But despite claims often made by one source or another, there is no well-agreed explanation for how this phenomenon occurs.
Water expands as it freezes into ice. In a pipe, ice forms first on the inside wall of the pipe and grows radially inward until there is a solid plug of ice blocking the pipe.
Another interesting thing with freezing water: The water in the hot-water lines freezes faster. This is insanely counterintuitive but true. You can easily demonstrate this by pouring two equal cups of water, heating one of them up, and putting both cups into the freezer.
A trickle of hot and cold water might be all it takes to keep your pipes from freezing. Let warm water drip overnight when temperatures are cold, preferably from a faucet on an outside wall. Adjust the thermostat. Keeping your thermostat set at the same temperature day and night may help prevent frozen pipes.
The rule of the thumb is that it takes roughly 6-hours for water in your pipe to freeze after left in an unheated area. Meaning if you lose power at your home and the weather is reaching below freezing point, you have approximately 6-hours until the pipes will begin to freeze.
Any of those circumstances could lead to pipes freezing – especially when the outside temperature is 20 degrees or colder. Generally, keeping your home at 55 degrees or warmer will prevent pipes from freezing.
No water or a slow trickle when a faucet is used. Whistling and banging coming from pipes, or strange bubbling sounds when you flush a toilet. Dampness, puddles, or rings on drywall or ceilings—signs of an urgent issue.
When the water freezes, it expands and can split or break the pipes. This can cause a major problem when the pipes thaw. When they thaw, the water at full pressure comes through and can flood your home which can cause significant further damage.
Risk of bursting
Frozen pipes will eventually thaw on their own, but it could take days or even weeks. If New York City is experiencing a brutal cold snap, the temperature could stay below freezing for many days. Meanwhile, the water in the pipes could be expanding.
And when it comes to preventing these headaches, PEX pays off. Not only does it add value to the installation because it's more freeze resistant than pipes like CVPC and copper, but it's also superior in every season, cold or not. Whether it's PEX-a, -b or –c, this pipe type is more freeze resistant than rigid pipes.
Harsh Winter
Some places have harsh winters and frozen pipes can lead to no running water. If you get lukewarm water (thus not hot or cold), this could be the issue. The pipes must gradually warm up before hot water will release from the faucet. You can use a hairdryer to unfreeze the pipes more quickly.
In addition to opening the door for mold and mildew growth, leaks in cabinets, walls, and floors can cost homeowners thousands in cleanup and repairs. The types of pipes most susceptible to freezing include outdoor spigots, swimming pool supply lines, and water sprinkler lines, but indoor pipes aren't necessarily safe.
Pipe freezing kits make pipework repair and maintenance a doddle without needing to drain down entire systems. You can save up to 85% on time and save money with minimum disruption and reduce the potential of water spillage and property damage.
The temperature of the pipe
If the temperature falls to 32 degrees or lower, your pipes are likely to freeze.
With this in mind, expect most pipes to freeze within six to eight hours. Uninsulated exterior pipes can freeze in under six hours if the temperature is below 20 degrees. It takes at least 12 hours for unprotected pipes to freeze at 32 degrees.
Pipes are most likely to burst when exposed to below-freezing conditions for six hours or more, which can happen throughout winter and early spring. Burst pipes could lead to a disaster, bringing severe water damage to your home.
Water freezes at 32° F, but setting your thermostat lower than 50° F puts your pipes at risk when you leave for a long time. However, if your indoor temperature is within the 50° to 60° range, you'll greatly reduce the risk of your indoor pipes freezing because your home won't drop to freezing temperatures.
Keep the Heat On
The ideal temperature would be around 55 to 60 degrees. This will be warm enough to keep pipes from freezing. This might seem too much for some homeowners due to the added costs in their expenses.
They use heating coils to heat the water that flows through the unit when needed. But any water still left in the pipes and unit at the conclusion of its last use can still freeze and burst the water heater.
If water in the pipes does not freeze at -40 degrees Celcius, there is a reason for that. Either the pipes are indoors in heated spaces, or they are heat traced, or they are drained, or they are insulated, or they are buried, or water in the pipes is running (or at least dripping), at least intermittently.
Freezing from the bottom up would happen with a pond full of acetone or olive oil. The reason water freezes from the top down is because, unlike almost everything else, water gets less dense when it freezes. This is why ice cubes float in a drink.
The temperature of icy winter can cause the hot water pipes to freeze or even crack. It is a strange thing that hot water pipes freeze quickly than cold water pipes. By increasing the temperature of your house, you can attempt to unfreeze the frozen pipe.