Power Outages, Storms and Your Heating System

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Bay Area winter storms are mostly wind and heavy rain rather than snow, but they still knock out power, drop trees on lines and put water where it does not belong. The surprise for many people is that the gas furnace goes cold the moment the lights do. Here is what is happening, how to stay warm without poisoning anyone, and what to check before you trust your heating system again.

This page is part of our Bay Area Winter Heating Help Center. If you smell gas at any point during a storm, stop reading and follow the steps on our gas smell and carbon monoxide page: get out, then call 9-1-1 and PG&E at 1-877-660-6789 (PG&E).

Why your gas furnace stops when the power goes out

A modern gas furnace burns gas, but electricity runs everything that makes burning it safe. The control board decides when to fire; the draft inducer fan clears the flue; the hot surface igniter or spark lights the burners; the flame sensor proves there is a flame; and the blower moves the heat through the ducts. Without power, none of that happens, and the gas valve stays shut. That is by design.

A heat pump or ductless mini-split is fully electric, so it stops too. The exception is some older wall and floor furnaces with a standing pilot and no blower. Many of these run on a small current the pilot flame generates, so they may keep working in a blackout. If yours does, keep its vent clear and make sure your carbon monoxide alarm still has battery power, because this is exactly the kind of night people stop paying attention to the heater.

During the outage: staying warm safely

Do

• Pick one room, ideally a small interior room or the one that gets afternoon sun, and bring everyone into it. Close the doors to the rest of the house.
• Close curtains and blinds once it gets dark; roll a towel against gaps under exterior doors.
• Dress in layers, wear a hat indoors, and use sleeping bags or piled blankets at night.
• Use flashlights and battery lanterns rather than candles.
• Switch the thermostat to off (or the furnace switch to off) so the system does not start and stop repeatedly as the power flickers back.
• Check on older neighbors and anyone living alone.

Never

• Heat the house with a gas oven or stovetop. The CDC puts it plainly: "Don't heat home with gas oven" (CDC).
• Bring a grill, camp stove or fuel-burning heater indoors, or into the garage. All of them make carbon monoxide.
• Run a generator in the house, garage or carport, even with the door open. More on that below.
• Warm up in a car running inside an attached garage.

What about the fireplace? A wood fire can help, with the damper open and a working CO alarm, but check first whether a Spare the Air alert is in effect. On an alert day it is illegal to burn wood, fire logs or pellets in a fireplace or wood stove anywhere in the Bay Area (Spare the Air). Alerts are most common November through February, and a no-burn alert can be called any day of the year. The Air District's exemption covers only homes without permanently installed heating that use a registered EPA-certified or pellet device, and an open-hearth fireplace does not qualify (BAAQMD).

A plug-in heater is only an option once power is back or on a properly connected generator, and the usual rules apply. See our space heater safety guide.

Generators: the rules that keep people alive

• Outside only, 20 feet away, exhaust pointed away. CPSC says to use portable generators outside only and at least 20 feet from the home, with the exhaust pointed away (CPSC). The CDC also says to keep them at least 20 feet from doors and windows (CDC). On a narrow Bay Area side yard that can be hard; if you cannot get 20 feet, do not run it. CPSC reports about 750 people died from generator-related CO poisoning from 2012 to 2022.
• Never plug a generator into a house outlet. Backfeeding the house wiring can energize the utility line and endanger line crews and neighbors. To run a furnace from a generator, have an electrician install a transfer switch or interlock, and ask whether your generator's output suits the furnace's electronics.
• Run a CO alarm on every level. CPSC advises CO alarms on every level of the home and outside sleeping areas. Hard-wired alarms should have battery backup (Santa Cruz County summary), but a plug-in alarm without a battery goes dark in an outage, exactly when you need it most.

When the power comes back

Give it a few minutes. Power often flickers on and off before it settles, and each flicker is a restart for the furnace, heat pump and thermostat. Once the lights have been steady, turn the thermostat back to heat and give the system several minutes: most furnaces run a short purge and ignition sequence before the burners light, and many heat pumps have a built-in restart delay.

If a standing pilot went out, PG&E's advice is to shut off the gas at the appliance's shutoff valve and wait five minutes for gas to disperse before relighting (PG&E). PG&E technicians can also relight pilots for residential gas customers; book through pge.com/appt (PG&E). Still cold after that? Work through our no-heat checklist, and read about HVAC electrical problems if you suspect surge damage.

After wind and flooding

Floodwater is the one storm problem you should never try to power through. Trane's furnace installation manual is blunt: "Do not use this furnace if any part has been under water. A flood-damaged furnace is extremely dangerous. Attempts to use the furnace can result in fire or explosion." It calls for a qualified service agency to replace all gas controls, control parts and electrical parts that have been wet, or the whole furnace if necessary (Trane manual). CPSC has long said that gas control valves that have been under water must be replaced, and that submerged fans, motors, electric circuits and venting systems should be evaluated by a qualified technician (CPSC). FEMA's recovery guidance also reminds storm survivors to make sure the furnace and water heater are operating safely before relying on them (FEMA).

In Bay Area homes the equipment most likely to get wet is a furnace in a crawlspace, a floor furnace below the house, a unit in a garage on a slab near grade, and heat pump outdoor units sitting on pads in low side yards. If water reached any of them, leave the power and gas to that equipment off and call for an inspection.

Wind damage is easier to spot. Walk around the house once it is safe and look for:

• A furnace or water heater vent cap blown off, or a flue pipe knocked crooked on the roof.
• Branches, leaves or a fallen fence panel against the heat pump or mini-split outdoor unit. Clear loose debris by hand with the unit's power off; leave bent coils or a damaged fan to a technician.
• Plastic vent pipes from a high-efficiency furnace cracked, disconnected or blocked by debris.
• A heat pump outdoor unit shifted off its pad or with refrigerant lines pulled.

Stay well away from any downed wire and call 9-1-1.

How we help after a storm

After an outage or flooding, our technicians check the system the same way every time: power and breakers, the control board and its fault history, ignition and flame proving, the venting from the appliance to the outside, and, for flooded equipment, every part the water reached. We will tell you plainly what can be repaired and what has to be replaced, and every repair carries our 1-year parts and labor warranty. More on everyday service is on our residential HVAC repair page.

Schedule a post-storm heating check

Frequently asked questions

Written and reviewed by Jim McKinny, owner of Cool Aid Air Conditioning & Refrigeration — California C-20 and C-38 licensed, EPA Universal certified, second generation of a family business serving the Bay Area since 1966. Every job we complete is backed by our 1-year parts & labor warranty.