Likely cause: the power is out

Why this happens

Trane explains that even though a gas furnace burns natural gas, it uses electricity to start and to run the motor and blower fan. The American Red Cross notes that an outage can affect heating along with lighting, cooking and refrigeration. When the power is out, the furnace can't run no matter how the thermostat is set.

What to do right now

1. Check whether neighbors or street lights are out too, and report the outage to your electric utility.
2. If only part of your house is dark and the neighbors have power, use the half the house lost power guide linked below.
3. Never heat the house with a gas stove or oven. Ready.gov warns that it raises the risk of carbon monoxide poisoning and can cause fires and burns, and CDC says never to heat your house with a gas oven. Don't bring a grill, a camp stove or an outdoor heater inside for warmth either. The Red Cross says never to use outdoor stoves or heaters indoors, and CDC says never to burn charcoal or use a portable gas camp stove indoors.
4. If you run a generator, CDC says to use a battery-powered or battery backup carbon monoxide detector in your home.
5. Ready.gov says to keep the generator dry and out of rain or flooding, because touching a wet generator or anything plugged into it can cause a shock. It also says to plug appliances into the generator with heavy-duty extension cords, to let it cool before you refuel it, and to follow the maker's instructions.
6. Run a generator only outdoors. CDC says to keep it more than 20 feet from windows, doors and vents, and CPSC says to point the exhaust away from the house. CDC and CPSC both say never to run one inside the home or garage, even with the doors and windows open. Don't connect a generator to your home's wiring to run the furnace. CDC says not to connect a generator to your home's electrical circuits without an approved automatic-interrupt device, because a generator that is still connected when power comes back can become a major fire hazard and can endanger utility line workers.
7. Use flashlights for light, not candles. The Red Cross gives this advice to prevent fire hazards during an outage.
8. If the house gets too cold, Ready.gov says to go to a community location with power, and the Red Cross notes that communities often open warming centers.
9. Unplug sensitive electronics. Ready.gov says power can come back with surges that cause damage.
10. When power is back, set the thermostat to Heat above the room temperature. If the furnace breaker is tripped, the Red Cross advises having an electrician inspect breakers that tripped during an outage before you turn them back on.

When to stop. If you smell gas or rotten eggs, leave the house without touching any switch and call 911 or your gas utility from outside. If a carbon monoxide alarm sounds, or anyone feels dizzy, sick or has a headache, get everyone outside to fresh air and call 911. If you see smoke or flames, get out and call 911. If the heat stays off after the power is back, start this guide again from the top, but leave any breaker that tripped during the outage off until an electrician has checked it, as the Red Cross advises. If you notice a burning plastic or electrical smell once the furnace runs, Carrier says to turn the furnace off and have a qualified HVAC professional inspect it before you use it again.

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