How Do I Keep My Tankless Water Heater From Freezing?
Tankless water heaters have built-in freeze protection — but it only works if the power stays on. Here's how a tankless unit freezes, why an Oklahoma ice storm is the real risk, and the steps to protect it before the first hard freeze.
Tankless water heaters have a well-earned reputation for being tough and low-maintenance, so a lot of homeowners are surprised to learn they can freeze and crack in a hard Oklahoma winter. A common call we get as the weather turns cold is from someone who just realized their tankless unit is bolted to a garage wall or the outside of the house, and they want to know whether they need to do anything before the first freeze. The short answer: usually just a little, but it’s worth understanding why — because the one failure that catches people off guard is tied to our weather, not the unit.
Why a tankless unit can freeze at all
A tank water heater holds dozens of gallons of warm water that take a long time to cool, which buys it some natural freeze resistance. A tankless unit is the opposite: it only heats water on demand, so between uses the water sitting inside its heat exchanger is just room-temperature water in a thin maze of metal tubing. In a cold enough space, that water can freeze.
When it does, the trouble isn’t the ice itself — it’s the expansion. Freezing water pushes outward hard, and the heat exchanger is packed tight with no room to give. A freeze can crack the exchanger or split the internal plumbing, which is among the costliest things that can go wrong with a tankless heater and is typically excluded from the warranty. So this is firmly in “an ounce of prevention” territory.
The part most people miss: freeze protection needs power
Here’s the piece that trips up even careful homeowners. Nearly every modern tankless water heater — gas or electric — comes with built-in freeze protection. Small internal heating elements kick on automatically when the temperature drops, keeping the heat exchanger above freezing without you doing anything.
But that protection is electric. It only works while the unit has power. And in central Oklahoma, the coldest nights often arrive with the ice and wind that knock the grid out. A tankless unit mounted in a garage or on an exterior wall, humming along on its freeze protection, is suddenly unprotected the moment an ice storm takes the power down — which is the exact moment it’s coldest outside.
That single scenario — a hard freeze plus a power outage — is behind most of the frozen tankless units we see. Knowing that changes what “protecting it” actually means.
What to do before the first hard freeze
How much you need to do depends on where your unit lives.
If it’s installed in a heated, interior space, you’re in good shape. The freeze protection will handle normal cold, and the surrounding warm air is a backstop. The main thing worth doing is confirming the unit stays powered — don’t switch off the breaker it’s on, and don’t unplug it, for the season.
If it’s in a garage, attic, unheated utility room, or on an exterior wall, take a few extra steps now:
- Insulate the exposed water lines running to and from the unit, and the condensate line on a condensing model. Pipe insulation is cheap and does real work here, because the lines often freeze before the unit does.
- Keep the garage door closed on cold days and nights. An open or drafty garage can sit near outdoor temperature.
- Leave the power on. Resist the urge to flip the breaker to “save energy” in winter — that disables the very protection you’re counting on.
- Know your unit’s drain-down steps. Most tankless heaters have isolation valves and drain ports specifically so you can empty the unit if it will lose power for an extended stretch. Your owner’s manual spells out the exact sequence for your model.
When an outage is coming
If the forecast calls for an ice storm or an extended outage during a hard freeze — and your unit sits somewhere cold — the safest move is to drain it so there’s no water left inside to freeze. On most models that means shutting off the gas and water, opening the isolation valves, and letting the unit drain through its service ports. If you’ve never done it, have a plumber walk you through it once or do the first one with you; after that it’s a ten-minute job you can repeat whenever the grid looks shaky.
A whole-home standby generator solves the problem a different way, by keeping the freeze protection powered through an outage. For homes that lose power often, that’s worth weighing — but for most people, insulating the lines and knowing how to drain the unit is plenty.
If you’re not sure whether your unit even has isolation valves, where your lines run, or whether your installation is exposed enough to worry about, that’s a quick thing for a pro to check. Our water heater repair and installation team can look at how yours is mounted, add line insulation where it’s needed, and show you the drain-down steps for your specific model so you’re ready when a freeze warning lands.
The bottom line
A tankless water heater won’t freeze on an ordinary cold night — its built-in freeze protection has that covered, as long as the unit keeps its power. The real risk in Oklahoma is a hard freeze that arrives with a power outage, especially for units in garages, attics, or on exterior walls. Insulate the exposed lines, leave the unit powered through the winter, and learn how to drain it if a long outage is coming. Those few steps head off a cracked heat exchanger, which is the kind of repair you’d much rather prevent.
Want someone to check whether your tankless unit is ready for winter — or help you drain it before a storm? Graco serves Edmond, Oklahoma City, and the surrounding metro with flat-rate pricing you approve up front before any work begins. Call (405) 500-5333 and we’ll help you get ahead of the first hard freeze.
Frequently asked questions
- Does a tankless water heater have freeze protection built in?
- Most modern gas and electric tankless units do — small internal heaters and, on many models, a recirculation feature keep the heat exchanger above freezing when it's cold out. The catch is that this protection runs on electricity. If the power goes out during a hard freeze, the freeze protection stops working, and that's exactly when an exterior or garage-mounted unit is most at risk.
- Will my tankless unit freeze if it's installed indoors?
- A unit in a heated, interior space is usually fine. The ones that get into trouble are mounted in a garage, an unheated utility room, an attic, or on an exterior wall — common spots in Oklahoma homes. Those locations sit much closer to freezing, and the exposed water and gas lines running to them can freeze even when the unit itself is okay.
- What happens if a tankless water heater freezes?
- Water expands as it freezes, and inside the tightly packed heat exchanger there's nowhere for that pressure to go. The result is often a cracked heat exchanger or split internal lines — one of the most expensive failures a tankless unit can have, and usually not covered under warranty when it traces back to freezing. That's why prevention is worth the small effort.