What to do if a carbon monoxide alarm goes off during a winter power outage with space heaters

Short answer

Why people ask this

In a winter power outage, people often turn to space heaters, generators, or fireplaces to stay warm, which changes the carbon monoxide risk. The alarm can be confusing when the house is cold and options feel limited. Battery-backed CO alarms may sound while electric heat is unavailable, and fuel-burning space heaters or nearby generators can create CO quickly. Snow can also block exterior vents and car tailpipes, making CO build up even if heaters seem to work. People want to know what is safe right now and what heat sources are okay until power returns.

When it might be safe

• The alarm stops after you immediately shut off all fuel‑burning space heaters, open doors/windows briefly for fresh air, and a CO reading returns to zero on a digital display.
• It was a single periodic chirp indicating low battery, not a continuous alarm; replacing batteries stops it and no other fuel source is running.
• You used an indoor-rated catalytic propane heater exactly as directed (window cracked per manual, CO alarm present), and the alarm only sounded when ventilation was closed—reopening ventilation and shutting the unit stops the alarm.
• The alarm is near a garage door where a car was briefly idling; after moving the car outdoors with tailpipe clear of snow and ventilating, the alarm clears and stays silent.

When it is not safe

• Staying inside while a continuous CO alarm sounds, even if it is very cold—leave for fresh air first.
• Running fuel‑burning space heaters, kerosene heaters, or grills indoors without proper venting and active CO monitoring.
• Using a generator in a garage, porch, or near doors/windows (keep it 20+ feet away and downwind).
• Heating the home with a gas oven or stovetop during the outage.
• Idling a car in an attached garage or with the tailpipe blocked by snow or ice.
• Re-entering before the alarm stops and a professional or fire department clears the home.

Possible risks

• Carbon monoxide poisoning from combustion heaters or nearby generator exhaust during the outage.
• Rapid CO buildup when snow or ice blocks furnace, water heater, or dryer vents and the home is sealed tight for warmth.
• Fire hazards from improper space heater use, extension cords, or tipping in cramped, cold rooms.
• Hypothermia if evacuation is delayed or if people remain in a cold, contaminated space instead of moving to safe shelter.
• Recurring exposure if the source (e.g., a heater or car with snow-clogged tailpipe) isn’t identified and corrected.

Safer alternatives

• Evacuate to fresh air, call 911 or the fire department, and move to a neighbor’s home, a warming center, or your car parked outdoors with the tailpipe fully cleared of snow.
• If using any fuel‑burning heater, switch to an indoor-rated model only, follow the manual exactly, crack a window as required, and keep a working battery CO alarm in the same area.
• Use layered clothing, blankets, and one room “heat trapping” (close interior doors, block drafts) while you wait for power to return, rather than running risky devices.
• If safe, open a few windows/doors briefly to flush the home after shutting off heaters; then keep them closed to conserve heat once the alarm clears.
• Place generators outdoors at least 20 feet away, downwind, with exhaust pointed away from the house; run heavy-duty cords through a window, not the garage.
• Check and clear snow from exterior vents (furnace, water heater, dryer) and from vehicle tailpipes before restarting any appliances or sitting in a warming car.

Bottom line

Treat the alarm as real: get everyone to fresh air, shut off space heaters and any combustion sources, ventilate briefly, and call for help. In a winter outage, prioritize safe shelter elsewhere over risky heat—no generators in or near the home, no ovens for heat, and only use indoor-rated heaters with ventilation and a working battery CO alarm. Clear snow from vents and tailpipes, and don’t re-enter until it’s declared safe.

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