Gas Smell or Carbon Monoxide Alarm: What to Do Right Now

Home › Winter Heating Help › Gas smell and CO alarms

If you smell gas or a carbon monoxide alarm is going off right now, read the red box below and then go outside. Everything else on this page can wait until you, your family and your pets are in fresh air.

This page is part of our Bay Area Winter Heating Help Center. It covers the exact steps, how to tell a real alarm from a chirp, the usual causes of carbon monoxide at home, California's CO alarm law and what a technician checks before your heater runs again.

If you smell gas: the steps, in order

1. Get everyone out. PG&E's instruction is to alert everyone nearby and leave immediately to an upwind location (PG&E gas safety). Do not stop to open windows or hunt for the source.
2. Do not make a spark. PG&E's list of possible ignition sources includes cell phones, flashlights, light switches, matches and vehicles. That also means do not touch the thermostat, unplug anything or use an electric garage door opener on the way out.
3. Call from outside. 9-1-1 first, then PG&E at 1-877-660-6789. Call from the sidewalk, not the doorway.
4. Stay out until the fire department or PG&E tells you the house is safe to enter.
5. Then deal with the appliance. If the leak was at your furnace, wall heater, gas valve or flexible connector, that appliance needs repair or replacement of the faulty part before it is lit again. That is the point where you call an HVAC company.

Should you shut the gas off at the meter? Only if responders ask you to, and let PG&E turn it back on and relight your pilots. A brief whiff at a stove burner as it lights is common. A smell you notice walking into a room, one that lingers, or one near the furnace closet is a leak until someone with a gas detector says otherwise.

If a carbon monoxide alarm goes off

Carbon monoxide gives no warning of its own. The CDC describes combustion exhaust as "a poison gas you cannot see or smell" (CDC). Your alarm is your only early warning.

Chirp or alarm?

A single short chirp every minute or so almost always means a low battery or an alarm that has reached the end of its service life (most carry an end-of-life date on the back). A real alarm is a loud, repeating pattern of beeps, and many voice models also say "carbon monoxide." If you are not sure which one you are hearing, treat it as a real alarm.

What to do

1. Get out first. Do not wait to feel sick. According to the CDC, people who are sleeping, drunk or under the influence of other substances can die from CO poisoning before they have symptoms (CDC). Wake everyone and carry out anyone who is drowsy.
2. Call 9-1-1 from outside and get medical attention for anyone with symptoms. PG&E's guidance says the same (PG&E carbon monoxide safety).
3. Only if it is safe and quick: PG&E also says to turn off the gas appliance you suspect and open windows if it is safe to do so. Never let that delay getting out.
4. Do not trust the silence. An alarm that stops after the windows are open has not fixed anything. The source is still in the house.
5. Have the appliance inspected before it runs again, by PG&E or a qualified professional, as PG&E advises.

Symptoms worth taking seriously

The CDC lists the most common symptoms of CO poisoning as headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion (CDC). They are easy to mistake for the flu. Patterns that point to CO: several people (or a pet) unwell at once, everyone better after leaving the house, worse in the morning after the heater ran all night. The California Department of Public Health notes that CO deaths occur most often in the cold winter months and that the highest number of deaths is among people aged 65 and older (CDPH), so check on older relatives who live alone.

Where carbon monoxide comes from in a Bay Area home

Anything that burns gas, wood or gasoline can make carbon monoxide. It becomes a problem when combustion goes wrong or the exhaust does not leave the house. These are the causes we look for first.

A cracked heat exchanger

The heat exchanger is the metal wall between the burner flames and the air your blower pushes through the house. It expands and contracts every cycle, and after many years it can crack or rust through. Then exhaust can mix with house air, or blower air can disturb the flames. Warning signs: the flames jump, flicker or roll when the blower starts, soot appears around the burners, or the CO alarm tends to go off while the heat is running. Many Bay Area homes still run furnaces and wall heaters that have been in place for decades. Our article on the hidden dangers of old heaters in Bay Area homes covers what age does to them.

Flame color and soot

Healthy natural gas flames are mostly blue with a crisp, steady shape. Lazy yellow flames, flames that lift off the burner, black soot on the burner area, dark streaks around a wall heater grille, or soot at the edges of supply registers all mean poor combustion. Look through the viewing window if your furnace has one. Do not remove the sealed burner cover to get a better look.

A water heater or furnace that backdrafts

Older tank water heaters and 80% furnaces rely on warm exhaust rising up a metal flue on its own. If that flue is blocked or disconnected, or a strong kitchen hood, bath fans and a dryer pull the house into negative pressure, exhaust can spill back into the room. Signs: melted or discolored plastic on the water heater's top fittings, scorch marks around the draft hood, rust or moisture on the flue pipe.

Blocked vents and wall and floor furnaces

Bird nests, a rain cap blown off in a storm, a flue pipe knocked loose during attic work, or firewood stacked against a high-efficiency furnace's plastic vent pipes can all trap exhaust. Wall and floor furnaces add their own risks: they vent through the wall or the roof and often sit right next to living space. Our page on wall and floor furnaces covers their venting and clearance checks, and pilot lights and ignition problems covers flames that will not stay lit.

The attached garage and anything run indoors

A car warming up in an attached garage, even with the big door open, can push CO into the house through the connecting door. The CDC is blunt about generators: "Never use a generator indoors, in garages, or carports" (CDC). It also warns: "Don't heat home with gas oven" (CDC). Barbecues and camp stoves belong outdoors too. If a storm has knocked out your power, our guide to power outages and storms covers safe ways to stay warm.

California's CO alarm law, in plain terms

• Who needs one: every existing dwelling unit that has a fossil fuel burning heater or appliance, a fireplace, or an attached garage must have a CO device listed by the State Fire Marshal. Single-family homes had until July 1, 2011, and all other dwelling units except hotels and motels until January 1, 2013 (Health and Safety Code 17926).
• Where they go: the law points to the building standards for new construction or the manufacturer's instructions. Under the current California Residential Code, as Santa Cruz County's building department summarizes it, that means outside each separate sleeping area near the bedrooms, on every occupiable level including basements, and inside any bedroom that has a fuel-burning appliance in it or its attached bathroom (Santa Cruz County summary).
• Rentals: the owner must maintain the devices, and the alarm must work when the tenant moves in. A tenant who finds one missing or faulty must tell the owner, who must fix it (Health and Safety Code 17926.1). More on this in renters' heating rights.

An alarm does not make an old furnace safe. PG&E says CO alarms "should be considered as a backup and not as a replacement for proper use and maintenance," and recommends having heating systems and fuel-burning appliances inspected by a qualified professional every year (PG&E). Test yours with the button and replace it by its end-of-life date.

Before your heater runs again: what a technician checks

After responders clear the house, keep the heater off until it is inspected. On a CO or gas-leak follow-up our technicians check:

• Leak testing the gas valve, connector and fittings at the appliance.
• Measuring CO in the flue gas and in the room air with a combustion analyzer, with the heater running.
• Inspecting the heat exchanger as far as it can be seen, and watching the flames as the blower starts.
• Checking the vent from the appliance to the roof or wall, and the draft at a shared water heater vent with the furnace, fans and dryer running.
• Checking the burners, flame sensor and pilot, and your CO alarm locations.

If we find an unsafe heat exchanger or vent, we will shut the appliance off, show you what we found and tell you plainly whether repair still makes sense. Separately, PG&E offers free gas appliance safety inspections and pilot relight appointments for residential customers, bookable at pge.com/appt (PG&E). For ongoing peace of mind, an annual furnace maintenance visit covers these same checks before the cold arrives.

Book a furnace safety inspection

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.