How to Detect Carbon Monoxide in Your Home

A furnace that starts acting up on a cold St. Louis night is more than a comfort problem. If a fuel-burning appliance is venting improperly, it can create carbon monoxide risk inside the home. Knowing how to detect carbon monoxide starts with one critical fact: you cannot reliably see, smell, or taste it. A working carbon monoxide alarm is the only dependable way to identify dangerous levels before they become an emergency.

Carbon monoxide, often called CO, is produced when fuels such as natural gas, propane, oil, wood, charcoal, or gasoline do not burn completely. Furnaces, water heaters, fireplaces, gas ranges, attached garages, and portable generators can all be potential sources. Most operate safely when installed, vented, and maintained correctly. Problems arise when equipment is damaged, blocked, neglected, or used in the wrong place.

The only reliable way to detect carbon monoxide

A listed carbon monoxide alarm is your first line of warning. It measures CO in the air and sounds an alarm when exposure reaches a dangerous level over a defined period. Unlike smoke, carbon monoxide does not create a visible cloud or a distinct odor. Waiting for a smell from your furnace or water heater is not a safe detection plan.

Install CO alarms on every level of your home, including the basement, and outside each sleeping area. Homes with bedrooms far apart may need more than one alarm on the same floor. Follow the alarm manufacturer's placement instructions, since requirements can vary by model and local code.

For added protection, consider an alarm in or near a room with a fuel-burning appliance, as long as the manufacturer permits that location. Do not place an alarm directly beside a furnace, fireplace, or gas range unless the instructions specifically say to do so. Heat, humidity, cooking activity, and normal appliance startup can affect readings or cause nuisance alarms.

Hardwired alarms with battery backup can be a practical choice during power outages, but battery-operated units also provide valuable protection when properly maintained. What matters most is having approved alarms in the right locations and keeping them ready to work.

Know the difference between an alarm and a low-battery chirp

A carbon monoxide alarm is designed to get your attention. The exact pattern differs by manufacturer, so every household should read the label and instruction booklet for its models. Generally, a loud repeating alarm pattern signals possible CO and calls for immediate action. A brief occasional chirp often indicates a low battery, end-of-life notice, or device malfunction.

Never assume a loud CO alarm is a battery issue. Get people and pets outside first, then call 911 or your local fire department from a safe location. Let trained responders determine whether carbon monoxide is present and when it is safe to return.

Many CO alarms have a limited service life, commonly five to 10 years. The date is usually printed on the back or side of the unit. Replacing batteries does not extend the sensor's life. If the alarm is expired, replace the entire device.

Test alarms monthly

Use the test button once a month to confirm the alarm has power and can sound. This does not prove the sensor can accurately measure carbon monoxide, which is why replacement at the manufacturer's stated end-of-life date matters. Change batteries when the device indicates they are low, and make it easy to remember by choosing a consistent annual household task.

Do not test an alarm by holding it near vehicle exhaust, a gas appliance, or any other combustion source. That can create an unsafe exposure and does not provide a reliable test.

Warning signs that deserve fast attention

Carbon monoxide itself gives no sensory warning, but an appliance or venting problem may show clues before an alarm sounds. These clues do not confirm CO, and they should not be ignored.

Look for soot or dark staining around a furnace, water heater, fireplace, or vent connection. Watch for excessive moisture on windows near an appliance, rusting flue pipes, loose venting, or a yellow or flickering burner flame where a steady blue flame is expected. A gas flame can look different by appliance type, so treat this as a reason for professional inspection rather than a diagnosis.

Other concerns include a fireplace that smokes into the room, a furnace that repeatedly shuts down, unusually stale or stuffy air near mechanical equipment, or a damaged chimney cap after a storm. Birds' nests, leaves, ice, and debris can obstruct exterior vents. In homes with high-efficiency furnaces, snow buildup around low exterior intake and exhaust pipes can also create a serious operating problem.

Symptoms in people can be another warning, especially when several people feel unwell at the same time or symptoms improve after leaving the house. Possible symptoms include headache, dizziness, nausea, weakness, confusion, chest discomfort, or shortness of breath. Children, older adults, pregnant people, and anyone with heart or respiratory conditions may be more vulnerable.

Symptoms alone can have many causes, including flu, dehydration, or other illnesses. Still, if CO is possible, do not try to sort it out from inside the home. Get outside and seek emergency help.

What to do if your carbon monoxide alarm sounds

Treat a CO alarm as urgent, even if no one feels sick and even if the alarm stops after a few minutes. Carbon monoxide levels can change as equipment cycles on and off, and opening doors or windows may temporarily reduce the concentration without fixing the source.

If an alarm sounds, take these steps:

• Move everyone outside into fresh air immediately, including pets.

• Call 911 or the local fire department from outside or from a neighbor's home.

• If anyone has symptoms, seek medical care and tell responders that carbon monoxide exposure may be involved.

• Do not reenter the home until emergency responders say it is safe.

• Do not restart the furnace, water heater, fireplace, or other suspected appliance until it has been inspected and cleared.

Do not open windows, hunt for the source, or try to silence the alarm before leaving. Those actions can delay your exit. A few minutes spent investigating indoors is not worth the risk.

Common carbon monoxide sources around a home

Your heating system is a common concern during winter, but it is not the only possible source. Fuel-burning appliances and engines need proper ventilation every time they operate.

Never run a vehicle in an attached garage, even with the garage door open. Exhaust can move into living spaces quickly. Keep portable generators outdoors and well away from doors, windows, vents, and garages. Charcoal grills, camp stoves, and propane heaters intended for outdoor use should never be used inside a house, garage, basement, or enclosed porch.

Gas ovens and ranges are for cooking, not space heating. Using an oven to warm a home can create carbon monoxide and fire risk. Fireplaces and wood stoves also need clear chimneys, proper draft, and regular maintenance. A closed or obstructed chimney can send combustion gases back into the home.

Preventing CO problems from your furnace and water heater

Annual professional service is one of the most practical ways to reduce carbon monoxide risk. A qualified technician can inspect burners, heat exchangers, vent connections, drainage, combustion air, safety controls, and system performance. This is especially worthwhile before sustained heating season, when furnaces may run for long stretches.

Change filters on schedule. A dirty filter does not directly create carbon monoxide, but restricted airflow can contribute to overheating, shutdowns, and unnecessary strain on heating equipment. Keep the area around your furnace and water heater clear so a technician can inspect it and so stored items do not block combustion air or vents.

Do not tape, disconnect, or repeatedly reset a furnace safety switch to keep heat running. A system that shuts down or produces unusual odors, soot, noise, or poor performance needs a proper evaluation. Repairing the cause is safer and usually less expensive than waiting for a larger breakdown.

For St. Louis homeowners, cold snaps, heavy snow, and aging gas equipment can all expose weaknesses in a heating system. Breeze Heating & Cooling can inspect furnace and venting concerns, explain what is happening in plain language, and help restore safe, dependable comfort.

A carbon monoxide alarm gives your household time to get out. Keeping it tested, replacing it on schedule, and having fuel-burning equipment checked regularly gives that alarm the best chance to be a warning rather than the first sign that something is wrong.