Can Hot Water Pipes Freeze & Why do They Freeze First

Have your hot water pipes frozen? Why has this happened? Is there anything you can do to fix it?

In this guide you will learn:

  • Common reasons your hot water pipes may freeze.
  • The science behind your pipes freezing.
  • Ways to prevent and repair them.

Can Hot Water Pipes Freeze?

Yes. Hot water pipes can freeze. This may seem counterintuitive, but hot water pipes are more likely to freeze than cold water pipes in certain conditions. We will discuss the reasons why later in this article. 

Can Pipes Freeze If There Is Hot Water in Them?

Yes. Having any amount of water in pipes during a cold snap can be risky. Even hot water pipes can freeze if temperatures drop low enough. As such, it is recommended to turn on your faucets during a cold snap. Even just a trickle can keep the water moving and prevent your pipes from freezing.

Can Pipes Freeze When Water Heater isn’t Working?

A water heater does exactly what it says on the tin –  it takes cold water from your pipes and heats it for use in your house. If your water heater is not working, you may find that you can’t get hot water for use in your showers and baths. 

However, your pipes freezing is usually unrelated to your water heater. Pipes are frequently outside the home while water heaters are inside – this means that, during a cold snap, outside pipes are more likely to freeze first. If your pipes freeze, the water heater will have to work harder. 

In short, it is the cold weather that is causing your pipes to freeze, not the water heater.

Why Do Hot Water Pipes Freeze First? 

The fact that hot water pipes can freeze first is counterintuitive to many. The reason that hot water may freeze before cold water, also known as the Mpemba Effect, is still a contested subject. However, there are a few suspected causes.

Firstly, hot water evaporates faster than cold water. This can be observed easily by looking at boiling coffee. The steam coming off from it is due to the water evaporating due to the heat. Evaporation causes the volume of the water to decrease.

As the volume of water decreases, the more susceptible it is too freezing. Just compare how much of the water in a pond freezes compared to the amount in a bowl.

As such, water in hot water pipes evaporates more quickly, causing the pipes to freeze more quickly.

Another hypothesis discusses the presence of dissolved gases in water. Hot water has fewer dissolved gases than cold water. These gases can make it easier for ice crystals to form. However, different gases are more soluble at different temperatures.

This means that there are temperature ranges where hot water will freeze more quickly than cold water due to the existence of tiny gas bubbles that have not dissolved.

Why Is My Hot Water Pipe Frozen But Not Cold?

As mentioned above, hot water may freeze more quickly than cold water since it evaporates more rapidly. Therefore, it is possible that your hot water pipe may freeze before your cold water pipes. However, if your hot water pipes have frozen, then it will not be long until your cold water pipes also freeze.

How Cold Does It Have To Be For Hot Water Pipes To Freeze?

Hot water pipes are not more resistant to the cold than other types of pipes due to the reasons mentioned previously. As such, hot water pipes will freeze when temperatures drop below 20 degrees Fahrenheit.

What To Do When Your Hot Water Pipe is Frozen

If you do discover that your pipes have frozen, there are a few steps you should take to help deal with this problem.

1: Keep the faucet running

As mentioned before, having even a trickle of water running reduces the chances of your pipes freezing drastically. This is because running water offsets the lost heat with new water being constantly brought in to replace it. 

For example, large rivers in the Arctic that are fast-moving do not freeze, while slow-moving streams in the same area can be frozen solid. The same principle holds in your pipes – if water is kept moving, it is much harder to freeze.

2: Locate the pipe 

The next step is to locate the pipe you believe to be affected. This can be done by:

  • Check appliances and taps that have reduced water pressure.
  • Follow the pipes leading down from these appliances.
  • Otherwise, check for pipes that have not been insulated or may have sustained damage.

3: Thaw the pipe

Once you have located the frozen pipe, you can take steps to start thawing it. Some methods of thawing pipes include:

  • Electrical Heating Tape: This special kind of tape connects to an electrical socket and distributes heat along the length of the tape. Wrapping it around a pipe can thaw it quickly.
  • Heat Lamp: A portable heat lamp is a great way to heat a large number of pipes. However, always keep the lamp at least 3 feet away from any flammable materials.
  • Hairdryer: While it may feel strange, applying the heat from a hairdryer to a specific pipe can help speed along the thawing process.

Be sure to run the faucet while you are thawing the pipes. This will allow water to escape during the process, rather than all at once. Doing so will reduce the pressure in the pipes and prevent them from bursting.

Hot Water Not Working During Freeze – Most Common Causes

Not having hot water during a freeze can be exceedingly uncomfortable. Some of the common causes for a lack of hot water include:

  • Water Leaks: In the winter, leaks become an even bigger problem. Not only is water escaping, but cold air may be getting in. This reduces the water temperature and may even cause your pipes to freeze.
  • Lower Temperatures: The drop in temperatures during the winter reduces the heat of the water coming into your house. Your water may feel colder because it takes longer for your heater to convert this cold water to hot water.
  • Issues with your heater: If you are having problems with your water heater, you may notice that water coming into your house isn’t as hot as it should be. Getting your heater serviced is the best way to solve this issue.

How Do I Keep My Hot Water Pipes From Freezing?

Some of the best ways to prevent hot water pipes from freezing include:

  • Sealing leaks: If you find any leaks that could be letting cold air in, sealing them is a great start. In sealing the leaks, you can protect your hot water pipes from freezing, even in the coldest of winters.
  • Use heat tape: Heat tape is a great way to prevent your pipes from freezing. This is done by wrapping your pipes with the tape and plugging the tape into an outlet. The tape then keeps your pipes from freezing. 
  • Keep your house warm: By keeping the heating on for longer, you allow hot air to circulate in the house, which can help reduce the chances that your hot pipes will freeze.
  • Insulating pipes: As mentioned previously, insulating your pipes keeps the cold out and prevents them from freezing. It is best to install insulation in outside and hard-to-reach areas.

When to Call a Professional

The best time to call a professional is before the problems arise. Getting a qualified plumber to check your pipes once a year or two is a great way to avoid any problems.

If your pipes have frozen and burst, however, you should call a plumber immediately. As well as this, any visible water damage needs to be dealt with as soon as possible 

If you notice either of these issues and do not feel comfortable fixing the problem yourself: contact a professional.

Scroll to Top