Everybody knows carbon monoxide is dangerous. Not many people know when their gas furnace was last checked to make sure it's burning clean and venting properly. Carbon monoxide (CO) has no color and no smell, which is why detectors and a yearly furnace inspection matter so much.
A gas furnace that's working right sends its combustion gases outside through the vent pipe. Problems like a cracked heat exchanger, a blocked or disconnected vent, or burners that aren't burning cleanly can let CO into your home. Here's what to watch for and what to do.
Safety first
- If your CO alarm sounds: get everyone, including pets, outside into fresh air right away, then call 911 from outside. Don't open windows and stay inside to "air it out."
- If anyone has symptoms (headache, dizziness, nausea, confusion), get them outside and call 911.
- Smell gas? That's a different problem, but just as serious. Leave, don't flip switches, and call your gas company or 911 from outside.
- Don't go back in until the fire department says it's safe.
What to check
Make sure you have working CO detectors
Put a CO detector on every level of the home and outside each sleeping area. Follow the maker's placement instructions. Many recommend keeping it at least several feet from the furnace, water heater or stove so normal startup puffs don't set it off. Test them monthly, and check the date on the back: CO sensors wear out and the units need replacing every several years.
Know the symptoms
CO poisoning often feels like the flu: headache, dizziness, tiredness, nausea, shortness of breath or confusion. A big clue is that several people (or pets) in the house feel sick at the same time, and they feel better when they leave home. If that sounds familiar, get everyone outside and call 911.
Look at the furnace flame
If you can see the burners through the sight glass, healthy flames are mostly blue and steady. Yellow, orange, lazy or floating flames, or soot around the burner area, can mean the furnace isn't burning cleanly. Don't open the burner compartment yourself. Just call for an inspection.
Check the vent pipe
Look at the vent pipe where you can see it: it should be firmly connected, sloped correctly and not rusted through, with no gaps at the joints. On high-efficiency furnaces, the white PVC pipes outside should be clear of debris and nests.
Watch for other warning signs
Stuffy or stale-smelling air, more condensation than usual on windows near the furnace, soot stains around registers or the furnace, or a pilot or burner flame that keeps going out are all reasons to get the furnace looked at soon.
Get a combustion and safety check every year
A proper inspection goes beyond a quick look. The technician checks the heat exchanger, tests combustion, measures CO in the flue and the living space, and makes sure the vent and draft are right. The fall, before the heavy heating season, is the best time.
Where carbon monoxide comes from in a home
Carbon monoxide is produced whenever fuel burns without enough oxygen to burn completely. A properly adjusted gas furnace burns cleanly and sends what it does produce out the vent. Trouble starts when something changes: a dirty or misadjusted burner, a cracked heat exchanger that lets combustion gases mix with the air the blower moves through your house, or a vent that's blocked, disconnected or not drafting properly.
Furnaces aren't the only source. Gas water heaters, gas stoves and ovens, fireplaces, generators, and cars running in an attached garage can all produce CO. That's why I tell everyone with any fuel-burning appliance to have CO detectors on every level, even if their furnace was just checked.
A furnace safety inspection is worth doing every fall. During a heating tune-up, Frost Fire checks the burners and flame, the heat exchanger, the vent connections and draft, and tests for carbon monoxide at the furnace and in the living space. If anything looks off, you'll get a clear explanation and an honest recommendation, whether that's a simple adjustment, a repair or, on an old furnace with a cracked heat exchanger, a replacement.
When to call a pro
- Your CO detector has gone off at any point, even once (after the fire department has cleared the home).
- The furnace flames look yellow or lazy, or there's soot around the furnace.
- The vent pipe is loose, rusted or disconnected.
- People in the home have unexplained headaches or flu-like symptoms that ease when they're away.
- It's been more than a year since the furnace was inspected.
Still not working?
Frost Fire Heating & Cooling: $59 diagnostic (waived with repair), same-day service, no weekend surcharge, 4.8-star rated. Licensed & Insured. Serving Raleigh, Durham, the Triangle, Clayton and surrounding areas.
Common questions
Can a furnace leak carbon monoxide?
Yes. A cracked heat exchanger, a blocked or disconnected vent, or poor combustion can let CO into the home. That's why gas furnaces need an annual safety check and every home with gas appliances needs working CO detectors.
Where should I put a carbon monoxide detector?
On every level of the home and outside each sleeping area, following the manufacturer's instructions. Don't rely on a single detector in the basement next to the furnace.
Does a heat pump or electric furnace produce carbon monoxide?
No. CO comes from burning fuel. All-electric systems don't produce it, but you still need CO detectors if you have any gas appliances, a fireplace or an attached garage.
What does a furnace safety inspection cost?
Frost Fire includes safety and combustion checks in heating tune-ups, and members get up to 15% off repairs. Our diagnostic for a problem call is $59, waived if you go ahead with the repair.
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