What should I do with an outdoor tankless heater during a freezing power outage?

MGI’s recommendation: Treat this as a time-sensitive freeze-protection problem. Contact a qualified provider for your exact tankless model now, and give them the outside temperature, outage start time, and whether the heater or pipes may already be frozen. Do not wait for hot water to stop before asking for direction.

If you smell gas, get everyone outside to a safe location. Do not use switches or phones inside. Call 911 and your gas supplier from safety. Do not approach the heater. Xcel Energy gas safety guidance Stay outside until the gas utility confirms it is safe to return. Utility gas-return guidance.

Built-in protection is not a blanket promise. Rinnai’s November 2018 RU-series manual warns that a freezing power or gas interruption requires draining, and that its freeze protection does not protect external piping and valves. The applicable procedure must match the model and installation. Rinnai N-series manual, freeze protection

The provider should establish whether a drain-down accessory exists, whether it actually operated, and what still requires attention. Ask them to give or carry out the approved procedure, including the heater, its condensate components, and connected equipment where applicable. Here, condensate means water produced as a condensing heater recovers heat from exhaust. Rinnai condensing-process explanation. A photograph of the unit and visible pipe arrangement can help them identify what is installed.

Do not assume opening one valve empties the whole system. Avoid improvised heat, electrical connections, or a copied procedure for another heater. If the equipment may already be frozen, tell the provider before any attempt to run it or refill it.

The household water system needs its own owner. Ask a qualified plumbing provider about exposed pipes and safe isolation if necessary. Draining the heater alone does not establish that the rest of the home is protected. If water is leaking toward electrical equipment, stay away from the wet area and request urgent electrical triage.

While waiting, keep people away from the affected equipment, record the outage and temperature history, and arrange another safe source of hot water or a temporary place to stay if needed. Confirm actual availability rather than relying on an assumed emergency response time.

Once the immediate risk is controlled, request a written outage plan for this installation: who to call, which approved protection is installed, and what conditions require draining. That is the lasting answer we would want before the next cold outage.