Keep Your Tankless Water Heater From Freezing

Even if the tankless water heater is meant to provide hot water on demand and indefinitely, it will not be able to if the water in the pipes freezes.

One of the numerous issues for tankless units is the water loss that occurs when pipes freeze.

If you live in an area where hard freezes are common, you can do a few things to reduce the chances of your tankless water heater freezing.

Rinnai RU199iP Tankless Hot Water Heater

What are the most effective methods for keeping the tankless unit from freezing?

Fortunately, there are several options for keeping the tankless water heater from freezing. The following are the most successful methods:

  • Clean any standing water.

The absence of a tank in a tankless water heater does not preclude water from standing in the system. When the temperature is cold, the water will ultimately freeze; once it does, the interior parts of the unit are more vulnerable to harm. If you intend to be gone for longer than 48 hours, you must empty the water heater to prevent water from freezing in the system.

Aside: High-end manufacturers offer units with built-in freeze prevention in conjunction with the water heater. Here are a couple of such examples:

    • Tankless water heaters have ceramic heaters on the heat exchangers, internal components, and water parts that activate when the temperature falls below 30 degrees.
  • When the temperature unexpectedly drops, the units have a backup system to safeguard them. When the internal temperature of the tankless unit falls below a certain threshold, a sensor will activate. It will automatically cycle the water unit for a few seconds. When the water temperature reaches roughly 58 degrees, the system cycles on and off until the risk of freezing is eliminated.
    • .
  • Keep a constant power supply nearby. Power is required for freeze protection systems to operate. When you cannot drain the system, installing an uninterrupted power source that supplies electricity to the protective system in the event of a power loss is preferable. Backup batteries and drain-down solenoids are excellent choices. 
  • Ensure that the system is properly insulated. You lessen the chance of freezing by insulating the tankless unit. Protecting the pipelines takes time, especially in places with low levels of protection. Narrow and attic areas are particularly vulnerable to freezing. For best results, utilize polyethene wraps, heat tape, or fibreglass insulation.


Anyone who lives in a location with cold temperatures even before November should insulate their whole home.

When insulating the pipes, remember that you must employ an electrical freeze-prevention device (a heater will suffice). No matter how chilly it gets in your living space, you must reduce your chances of freezing.

  • Consider adding a recirculation system. If the device is compatible, consider installing a recirculation system. The system will provide instantaneously hot water while keeping the plumbing system warm in the winter. It can reduce the risk of freezing. When temperatures are below freezing, the recirculation system will efficiently support the freezing risk under control. 
  • Attempt to keep the plumbing system operational.

Running water will always freeze faster than standing water. If you’ve exhausted all other options and are still concerned about freezing, leave a tiny quantity of water running through the system at night. Most pipelines may be kept safe from freezing by using 1/10GPM.

Switching on all fixtures is unnecessary; only one would suffice. Ensure that the installation is linked to the tankless water heater.

  • Install the tankless water heater in a warm location. If you install the tankless water heater in a hot area, you may limit the chance of the system freezing. If such a warm spot is not accessible, you may at least search for a protected position to keep the cold at bay. It would be best to locate the vents away from where the wind usually blows. Be bold and construct a tiny lean-to to protect the tankless water heater. You may take wind protection to the next level by integrating vent terminations.


Top Choice

Rinnai RUC98iN (9.8 GPM)

Rinnai RUC98iN

Rheem RTGH-95DVLN (9.5 GPM)

Rheem RTG-95XLN-1


Should your tankless water heater be winterized?

Winterizing the tankless water heater is an effective safeguard, particularly if you intend to leave for the winter.

Always start by reading the owner’s handbook for instructions. Remember that the instructions are only for general assistance, and individual units may have specific needs.

If you have a gas-powered appliance, switch off the gas first. Here’s what you should do to protect the water supply:

  • Turn off your tankless unit’s cold water supply.
  • Drain the cold and hot water pipes by opening the drain down (freezing protection) solenoid valves.
  • You should empty your squad this way and turn on a few hot water faucets throughout the home.
  • Continue by removing the intake filter from the cold water line.
  • You must install the plug/inline filter on the hot water side.
  • Check for any remaining water in the pipes and allow for some expansion.
  • Keep in mind that not every system has hot water line fittings.

It would be best if you additionally considered the power supply:

  • Begin by shutting off the electricity to the device.
  • It depends on your system’s wiring, but normally you turn off the circuit breaker or disconnect the water heater.
  • Your tankless water heater will be safe if there is a power spike or loss.

Anyone who uses a gas-fired tankless water heater should additionally look after the vent system:

  • You must install a cover over the intake and exhaust vents.
  • Only do it if you can get there safely.
  • Debris, leaves, and even small animals are known to become lodged in the flue.
  • When restarting the unit, airflow issues may arise, so look for any stuck leaves.

Final word

Only some have the time or ability to winterize a tankless water heater. For winterizing, choose a competent plumber. He must guarantee the job and reimburse the costs if the assignment is incomplete. Make the most of it and sit next to him so you can do it on your own next year!