Can Water Heaters Freeze? What Happens If They Do?

When temperatures drop, most homeowners think about frozen pipes, but few consider their water heater. Although water heaters are designed for year-round performance, many are installed in garages, crawl spaces, or other unheated areas where freezing temperatures are a real possibility—and so is damage to water heaters. 

Understanding when and why this happens is key to protecting your home and your equipment. Let’s take a closer look at why water heaters can freeze in cold conditions. 

What Actually Happens When a Water Heater Freezes? 

When a water heater freezes, the damage is driven by basic physics. As water freezes, it expands. Inside a water heater or connected water heater pipes, that expansion creates intense internal pressure that rigid components aren’t designed to absorb. Ice forming within supply lines, outlet connections, valves, or internal passages can place stress on fittings and joints, gradually weakening them. In more severe cases, tanks, heat exchangers, or internal components can crack under the force. 

What makes this especially problematic is that it isn’t always immediately visible. Internal fractures or stressed water pipes connected to the heating system may remain intact while temperatures stay cold. Once conditions warm and the ice thaws, that hidden damage often reveals itself suddenly, through leaks, water loss, or system failure. 

Because freeze damage is caused by expanding ice inside rigid components, some water heater designs are inherently more vulnerable than others, especially tankless systems. 

Why Are Tankless Water Heaters More Prone to Freezing? 

Tankless water heaters operate differently from traditional tank systems. Instead of storing a large volume of water, they rely on compact internal waterways that heat water on demand. While this design offers efficiency benefits, it also increases susceptibility to freezing. 

The narrow channels inside a tankless unit allow water to freeze more quickly, even during short periods of extreme cold. When ice forms in these confined passageways, pressure builds rapidly. This can fracture or deform the heat exchanger, restrict flow, or damage internal valves and sensors, often resulting in a tankless hot water problem that prevents the system from operating properly even once temperatures rise again. 

Additionally, tankless water heaters can often freeze during power outages. Most tankless models include built-in freeze protection, but these features depend on uninterrupted electricity. Without power, water inside the unit can freeze quickly, even if outdoor temperatures hover just below freezing. For installations in unconditioned spaces or exterior enclosures, additional steps—such as insulating supply lines or taking measures to insulate a tankless water heater—may be necessary to reduce risk during cold weather. 

When freezing disrupts how a water heater functions, homeowners often feel the impact in multiple ways, not just at the unit itself. 

What Are the Consequences of a Frozen Water Heater? 

When a water heater freezes, the damage rarely affects just one component. Because ice expansion places stress throughout the system, the effects are often widespread and disruptive. 

One of the most immediate outcomes is no hot water, as damaged internal components, valves, or sensors prevent the system from operating safely. In other cases, frozen and expanding water can crack or burst supply and outlet pipes, leading to a water heater leaking once temperatures rise and the ice thaws. Tanks may rupture, and heat exchangers can fail under pressure, rendering the unit unsafe or inoperable. 

Beyond mechanical failure, leaks caused by freeze damage can result in significant property damage to floors, walls, and nearby structures. Even when damage appears minor, repeated freeze–thaw stress can weaken components over time, reducing overall system reliability and shortening the water heater’s lifespan. 

In many cases, the damage caused by freezing is extensive enough that repair is impractical or unsafe. When critical components fail, or the tank or heat exchanger is compromised, full replacement is often the most reliable long-term solution. Because the consequences of a frozen water heater can include leaks, system failure, and costly damage, taking proactive steps to prevent freezing is the most effective way to protect your home and your water heating system. 

How Can Water Heater Freezing Be Prevented? 

Preventing water heater freezing starts with managing the environment around the system and preparing it for cold conditions before temperatures drop. Proper protection reduces stress on internal components and helps maintain reliable operation throughout winter. 

One of the most important steps is insulating exposed hot and cold water lines. Plumbing pipe insulation helps slow heat loss and lowers the risk of ice forming inside supply and outlet piping, particularly in unheated spaces like garages, basements, crawl spaces, or exterior enclosures. Improving water heater insulation around the unit itself or upgrading the surrounding enclosure can also help retain warmth in colder environments. 

In regions that experience extreme cold, approved localized heat sources may be used to protect nearby plumbing. Some homeowners also allow a small, steady flow of water during severe cold spells, which can help prevent freezing in vulnerable lines. For systems equipped with active freeze protection, maintaining electrical power is critical. Without it, protective features cannot operate as intended. 

For vacant or seasonal properties, draining the water heater and connected plumbing is one of the most reliable ways to eliminate freeze risk entirely. This approach is especially important when the system will be exposed to freezing temperatures for extended periods without supervision. 

These precautions are particularly important for tankless water heaters. Because they contain smaller internal waterways and rely on powered freeze protection, they freeze faster than storage tank systems if conditions are not properly controlled. Using heated water pipes, insulation accessories, and winterization best practices can significantly reduce the likelihood of cold-weather damage. 

For more info, see our Winter Prep Tips for Water Heating Systems blog. 

What Should You Do If a Water Heater Freezes? 

Responding incorrectly to a frozen water heater can worsen existing damage or create new safety risks. If you suspect freezing, follow these steps to reduce the chance of further issues: 

1. Shut off power or fuel to the unit
   Turn off the gas or electrical supply immediately. Operating a frozen system can cause severe internal damage or create safety hazards. This is also a good time to locate the water heater’s shut-off valve if you’re not already familiar with it. 
2. Turn off the water supply
   Shutting off the incoming water helps prevent flooding once the ice inside the system begins to thaw. This step is especially important if frozen piping or internal components may already be compromised.
3. Allow the unit to thaw gradually
   Never attempt to force thawing with high heat or by restarting the system. Let the water heater and surrounding plumbing warm up naturally. If damage is suspected, you may choose to drain the water heater to relieve pressure and reduce stress on weakened components. 
4. Inspect for visible damage and leaks
   After thawing, carefully check the unit and nearby plumbing for cracks, moisture, or signs of water heater leaks. Even small leaks can indicate internal damage that may worsen over time. 
5. Contact a licensed professional if problems are found
   If any damage is detected or if the system does not operate normally after thawing, a licensed professional should evaluate the water heater to determine whether repair or replacement is the safest option. 

Need Help or Not Sure What to Do Next? 

If you’re unsure how to safely shut off your water heater or suspect freeze damage, contact a Rheem pro to start a conversation about the next best steps for your home. 

Frequently Asked Questions 

Can a water heater freeze even if it’s installed inside a building?
Yes. Garages, utility rooms, and basements can still drop below freezing if they are not properly insulated or heated. 

Do freeze protection features prevent all freeze damage?
No. Freeze protection reduces risk but depends on continuous power and does not protect against extended outages. 

Will freeze damage always be obvious right away?
Not necessarily. Some damage only becomes apparent after the system thaws and pressures stabilize. 

Can freeze-damaged components be repaired?
Minor pipe or valve damage may be repairable, but cracked tanks or heat exchangers typically require replacement. 

Does letting faucets drip during cold weather help?
Yes. Maintaining water movement reduces the likelihood of ice formation in water supply lines.