Winter brings a special challenge for homeowners with tankless water heaters. These compact, energy-saving units can deliver endless hot water—unless freezing temperatures cause damage. When pipes or internal parts freeze, you risk leaks, costly repairs, or even total system failure. The good news? With a few smart steps and the right tools, you can keep your tankless water heater safe and running strong all winter long. Here’s how to protect your investment, plus the best accessories to prevent freezing—whether your heater is indoors, outdoors, or in an unheated space.
Quick Picks: Best Products to Prevent Tankless Water Heater Freezing
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Best Overall:
Frost King Electric Pipe Heat Cable Kit – Automatic heat cable to keep supply and drain lines from freezing. -
Best Budget:
Camco Water Heater Blanket – Simple insulation wrap for water heaters and exposed pipes. -
Best Premium:
Thermo Cube Thermostatically Controlled Outlet – Automatically powers heat cables or heaters only when temps drop near freezing.
Why Tankless Water Heaters Freeze (and How to Stop It)
Unlike bulky tank heaters, tankless models have thin internal pipes and small chambers. Even a few hours of freezing air can cause major problems. Most tankless heaters have built-in freeze protection, but it only works if there’s power and the unit is installed correctly. Here’s what can go wrong:
- No Power: Built-in freeze protection needs electricity. Outages leave your unit exposed.
- Uninsulated Pipes: Water lines in unheated areas freeze fast.
- Wind Chill: Outdoor units and pipes facing wind freeze much quicker, even if air temps are just below freezing.
- No Water Movement: Stagnant water is more likely to freeze. Running a slow drip can help in emergencies.
- Poor Installation: Gaps in insulation or exposure to drafts can defeat factory freeze protection.
The key to freeze protection is combining insulation, heat, and water movement—plus a few extra steps if you’ll be away from home.
How to Keep a Tankless Water Heater from Freezing: Step-by-Step
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Insulate All Exposed Pipes
Use foam pipe insulation on both hot and cold water lines leading to and from the heater. For extra protection, add a water heater blanket or wrap the heater itself if it’s in a garage, crawl space, or outdoors. -
Install Heat Cable on Vulnerable Pipes
Wrap a heat cable, like the Frost King Electric Pipe Heat Cable Kit, around exposed water lines. These cables turn on automatically when temps drop, preventing ice formation. -
Use a Thermostatically Controlled Outlet
Plug your heat cable or small space heater into a Thermo Cube outlet—it only supplies power when temps fall below ~35°F, saving energy and providing peace of mind. -
Keep Power On for Built-in Freeze Protection
Never unplug your tankless water heater in winter. The internal heater or recirculation system only works with power. If you expect an outage, drain the unit (see below). -
Seal Gaps and Block Drafts
Make sure walls, enclosures, or vent openings near the unit are sealed. Wind chill rapidly increases freezing risk. -
Run a Trickle of Water in Extreme Cold
Letting a hot tap run at a slow drip keeps water moving through the system, making freezing much less likely during cold snaps or blackouts. -
Drain the Unit if Leaving Home or During Prolonged Outages
If you’ll be away for days, or if power goes out for an extended period, shut off water and gas/electric, then open the drain valves. Consult your heater’s manual for the correct procedure. -
Consider a Heated Enclosure for Outdoor Units
Special outdoor-rated water heater covers or insulated boxes add another layer of protection for cold climates.
Best Products to Prevent Tankless Water Heater Freezing
Frost King Electric Pipe Heat Cable Kit
Who it’s for: Homeowners with exposed pipes in cold garages, crawl spaces, or outdoors.
Key Benefits:
- Keeps pipes from freezing automatically
- Works on both copper and plastic pipes
- Installs in minutes—just wrap and plug in
- Low energy draw, high reliability
- Built-in thermostat
Pros:
- Peace of mind in any freeze event
- Simple, effective, affordable
- Reusable every winter
Cons:
- Needs an outlet nearby
- Can be tricky to install in tight spots
Final Verdict: The best all-around solution for exposed water lines—works perfectly with tankless units.
See it on Amazon
Camco Water Heater Blanket
Who it’s for: Anyone with a tankless unit in a chilly garage, crawlspace, or attic.
Key Benefits:
- Adds insulation and retains heat
- Cuts heat loss for better freeze prevention
- Fits most water heater sizes
- Easy DIY install with included tape
- Budget-friendly way to boost protection
Pros:
- Low cost
- Improves energy efficiency too
- Quick to install
Cons:
- Not a substitute for active freeze protection in severe cold
- Can be bulky around pipes and valves
Final Verdict: Simple, effective insulation that pairs well with any heat cable or built-in heater.
Check price on Amazon
Thermo Cube Thermostatically Controlled Outlet
Who it’s for: Homeowners who want a “set-and-forget” solution for heat cables or space heaters.
Key Benefits:
- Turns power on/off automatically based on air temperature
- Eliminates wasteful energy use
- Works with heat cables, small heaters, or even heat lamps
- No wiring—just plug in
- Reliable for years of freeze protection
Pros:
- No need to monitor weather constantly
- Saves energy and extends cable life
- Fits any standard outlet
Cons:
- Only works in areas with power
- Won’t help during an extended outage
Final Verdict: The best way to automate freeze protection for any accessory.
See it on Amazon
Comparison Table
| Name | Key Features | Specs/Capacity | Price Link |
|---|---|---|---|
| Frost King Heat Cable Kit | Automatic, easy wrap, built-in thermostat | Up to 30 feet, 120V, fits all pipes | View |
| Camco Water Heater Blanket | Insulation, easy install, fits all | Up to 60-gallon heaters, 3” thick | View |
| Thermo Cube Outlet | Thermostat control, plug-in, set & forget | Two outlets, on at 35°F, off at 45°F | View |
FAQ: Protecting Tankless Water Heaters from Freezing
- Does my tankless water heater have freeze protection?
Most modern units include internal heaters or recirculation for freeze protection—but only when powered on and properly installed. - Will freezing void my warranty?
Yes—damage from freezing is almost always excluded. Always follow manufacturer’s instructions for winterizing and freeze prevention. - What if I lose power in a freeze?
Immediately drain your tankless water heater and pipes, or keep water moving with a trickle if draining isn’t possible. - Should I insulate pipes if my heater is inside?
Yes—pipes in basements, garages, crawl spaces, or exterior walls are still vulnerable. - How do I drain my tankless heater?
Shut off power and water, open drain ports, and follow your owner’s manual for the safest method.
Conclusion
Don’t let a winter freeze turn your tankless water heater into an expensive repair. With proper insulation, heat cables, smart outlets, and good winter habits, you can protect your system for many seasons to come. Invest in the right gear, check your heater before the first freeze, and enjoy hot water with confidence—even when the temperature drops.