Is your furnace leaking carbon monoxide? It is the question every Orange County homeowner should ask the first time the heater runs each fall. Furnaces here sit idle for six or seven months, and a cracked heat exchanger or blocked flue often shows itself only once the system fires up again. Carbon monoxide (CO) is odorless and invisible, so you cannot rely on your nose. Here is what the warning signs look like, what California requires, and exactly what to do, from the team at South County Air Services serving Mission Viejo, Laguna Niguel, San Clemente, and the rest of South County.
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For a faster response, text. Limited time. Cannot be combined with any other offer.How a Furnace Can Leak Carbon Monoxide
A gas furnace burns natural gas inside a sealed combustion chamber. The heat exchanger, a set of metal tubes or clamshells, keeps the exhaust gases (including CO) separate from the air blowing through your vents. When that metal cracks or corrodes, or when the flue is blocked, CO can enter your home. Typical causes include:
- Age: most furnaces last 15 to 20 years, and heat exchangers are the most common failure point on older units.
- Overheating: a dirty filter or restricted airflow makes the heat exchanger flex and crack over time.
- Blocked flue or vent: bird nests, debris, or a disconnected vent pipe push exhaust back into the house.
- Dirty burners: poor combustion produces more CO than clean burners do.
Warning Signs of a Furnace Carbon Monoxide Leak
Because CO has no smell, look for the clues around it. Call a licensed technician if you notice any of these:
- Headaches, dizziness, nausea, or flu-like symptoms that improve when you leave the house
- A yellow or flickering burner flame instead of a steady blue one
- Soot, rust streaks, or scorch marks around the furnace or flue
- Excess moisture or condensation on windows near the furnace
- A CO alarm that sounds, even once
- Pets or several family members feeling unwell at the same time
Mild exposure feels like the flu, which is why CO poisoning is so often missed. Higher levels cause confusion and loss of consciousness. Treat any alarm as real.
California CO Alarm Rules Every Orange County Homeowner Should Know
California law requires carbon monoxide alarms in single-family homes with a fossil-fuel appliance, an attached garage, or both, and the requirement extends to rentals and to homes being sold. Installation guidelines generally call for an alarm outside each sleeping area and on every level. Most alarms need replacing every 5 to 10 years (check the date printed on the back), and batteries should be tested monthly. If your Rancho Santa Margarita or Lake Forest home was built in the 1990s and the alarms look original, replace them now.
What to Do If You Suspect a Furnace Carbon Monoxide Leak
- Get everyone outside into fresh air, including pets, then call 911 if anyone feels ill.
- Do not re-enter until the fire department says it is safe.
- Turn off the furnace only if you can do so without staying in the house.
- Do not restart it until a licensed HVAC technician has inspected the heat exchanger, flue, and burners.
A professional furnace safety inspection typically includes a visual and camera check of the heat exchanger, a flue draft test, burner inspection, and a CO reading at the supply registers. At South County Air Services we do this as part of our heating tune-ups, and it is the part homeowners most often skip.
Repair or Replace a Cracked Heat Exchanger?
A cracked heat exchanger is not a DIY fix and cannot be safely patched. Replacing the part on a newer furnace under warranty can be reasonable, but out of warranty it commonly runs roughly $1,500 to $3,500 or more in Orange County, which is often close to half the cost of a new furnace. On a furnace over 15 years old, replacement is usually the smarter long-term investment. Ask for a written explanation and photos of the crack, and do not hesitate to get a second opinion from a licensed contractor.
Frequently Asked Questions
Can a furnace leak carbon monoxide even if it seems to work fine?
Yes. A furnace with a cracked heat exchanger can heat your home normally while leaking CO, which is why working CO alarms and an annual inspection matter more than how the heat feels.
How often should I have my furnace inspected in Orange County?
Once a year, ideally in early fall before the first cold night. Furnaces over 10 years old benefit most from a heat exchanger inspection.
Do electric heat pumps produce carbon monoxide?
No. Heat pumps and electric furnaces do not burn fuel, so they cannot produce CO. Gas water heaters, stoves, and fireplaces still can, so keep alarms working either way.
Is a CO alarm the same as a smoke alarm?
No. Smoke alarms do not detect carbon monoxide. You need a dedicated CO alarm or a combination unit that is listed for both.
Schedule a Furnace Safety Inspection in South Orange County
Worried about a furnace carbon monoxide leak in your home? South County Air Services is a local, family-owned HVAC company serving Mission Viejo, Laguna Niguel, San Clemente, Dana Point, Aliso Viejo, Rancho Santa Margarita, and Lake Forest. Email us at support@southcountyairservices.com or visit southcountyairservices.com to book a heating safety inspection before the cold sets in.