Will a gas water heater work during a power outage?

Atmospheric-vent tanks with a standing pilot keep working. On these heaters a part called a thermopile (or a thermocouple on older valves) sits in the pilot flame and turns heat into a tiny electrical current, measured in millivolts. That current holds the gas valve open and, on newer valves, runs the control board.

Bradford White's spec sheet for its atmospheric-vent ICON System models describes exactly that setup: a thermopile turns pilot-flame heat into electricity to run the gas valve and its microprocessor, with no need for external electricity. Many standard atmospheric tanks from other makers work on the same millivolt principle.

You can usually spot one in about ten seconds:

• No power cord or electrical box on the heater.
• A metal draft hood on top, feeding a vertical metal flue pipe.
• A gas control knob on the front with pilot and temperature settings, often with a push-button igniter.

If your heater looks like that, it should keep making hot water through an outage. Clean and simple.

Anything that plugs in stops. That covers three common types.

Power vent tanks. These use an electric blower to push exhaust out through a plastic pipe, usually through a wall. Bradford White's power vent spec sheet lists 120 VAC as required for power venting, at 3.1 amps. No power means no blower, and the burner will not light without it. If yours has a fan housing on top and a cord, see our page on a power vent water heater whose blower runs but the burner won't light for how that system is supposed to behave.

Gas tankless heaters. A. O. Smith says flatly that gas tankless water heaters need electricity to run, so they stop working during power outages. Rinnai's FAQ says the same about its own units: if you experience a power outage, your Rinnai tankless water heater will not operate. The electricity runs the ignition, control board, fan and safety sensors, even though gas does the heating.

Gas tanks with electronic ignition. A. O. Smith notes this is true of most water heaters used today, including newer gas tank models with electronic ignition. Some high-efficiency and low-emission tanks fall in this group.

Electric tanks and heat pump (hybrid) heaters obviously stop too, since electricity is their only heat source. Our gas vs electric water heater page covers those trade-offs in full.

### How long does the hot water last once the power is out?

Even a heater that stops firing still has a tank full of water that was hot when the lights went out. A tank model, gas or electric, holds that heat for hours because the tank is insulated, so you can usually get through the evening's dishes or a short shower. A tankless unit has no stored supply. The hot water ends when the hot water already sitting in the pipes runs out.

A standing-pilot tank behaves almost normally. It reheats after each draw, just as it always does. The one thing to watch is the pilot itself. If it goes out for an unrelated reason during the outage, relight it by the instructions on the heater's label, and see why a pilot light won't stay lit if it keeps dropping out.

Yes, with the right setup. Gas tankless units draw very little power. A. O. Smith puts it at about 100 to 150 watts for a few seconds at startup, then 60 to 100 watts while running, and says battery backup systems are available for tankless water heaters. Rinnai sells a battery backup it says can run its tankless units for multiple days.

Look, a generator works too, but how you hook it up matters:

1. 1Run any portable generator outside only. The Consumer Product Safety Commission says never to operate one inside a home, garage, basement, crawlspace or shed, or near a window or exterior vent. A garage with the door open still counts as a garage.
2. 2Feed it the way the maker specifies. A. O. Smith says its gas tankless units should be plugged into a 120VAC, 60Hz grounded electrical outlet, with the installation following local electrical code. Backfeeding house circuits from a generator is electrician work, done with a proper transfer switch or interlock.
3. 3Plan it before you need it. Sorting out a backup in the dark during a storm is how mistakes happen.

If you smell gas at any point, leave the house first and call the gas company from outside. Do not flip switches or try to relight anything. That rule does not change because the power is out. A water heater that smells like gas is covered on our pilot light out and gas smell page.

Otherwise, the steps are short:

1. 1Standing-pilot tank: check that the pilot is still lit after the outage. Nothing else is needed.
2. 2Power vent or electronic ignition tank: when power returns, it should restart on its own at the next call for heat. If it doesn't, check the outlet and breaker, then look for a status light code on the control.
3. 3Gas tankless: turn on a hot tap and watch the display. If it stays blank or shows an error, our guide on a tankless water heater not working after a power outage walks through the checks in order.

For most Phoenix homes, probably not. Many outages are short, and a tank keeps its stored hot water for hours even without power. But if your neighborhood loses power a few times every monsoon season, or someone in the house relies on hot water for medical reasons, outage tolerance is a fair tiebreaker. A standing-pilot atmospheric tank needs no electricity at all. A tankless or power vent model trades that for efficiency or venting flexibility, and a battery backup closes most of the gap.

We install and replace gas tank and tankless water heaters across the Valley, and we can tell you which type your house can vent and supply before you buy. See our water heater service for the details.