Signs of a Carbon Monoxide Leak in Your House — and How to Confirm It

Carbon monoxide is called the silent killer for a reason: it has no color, no smell, and no taste. You cannot detect it without a sensor. That said, there are indirect signs — from your body, your appliances, and your environment — that can suggest CO may be present.

Physical Symptoms as a Clue

If CO is accumulating in your home, the first indication is often how you feel. Low-level CO exposure produces symptoms that are easy to dismiss:

• Persistent headache, especially across the forehead — often the first sign
• Mild nausea or dizziness that improves when you leave the house
• Fatigue disproportionate to your activity level
• Shortness of breath during light exertion
• Multiple people in the home feeling ill simultaneously — a critical indicator

Appliance Warning Signs

CO is produced by incomplete combustion. Your fuel-burning appliances can give visual clues that something isn't burning correctly:

• Yellow or orange flame on a gas burner instead of blue — indicates incomplete combustion and elevated CO production
• Soot or black marks around burners, furnace vents, or fireplace openings
• Excessive condensation on windows near appliances — a sign of combustion gases venting indoors
• A furnace that cycles on and off more frequently than usual
• Visible rust or corrosion on flue pipes or vent connections

Environmental Clues

• Other people in adjacent units (apartments, condos) reporting similar symptoms simultaneously
• Pets acting lethargic or disoriented — animals often show CO symptoms before humans due to smaller body mass
• A gas stove that burns with an uneven or yellow flame
• A fireplace that smells of exhaust rather than burning wood when in use

The Only Way to Confirm It

Physical symptoms and appliance clues are indicators — not confirmation. The only way to know whether CO is present is a sensor reading. A live PPM display gives you an immediate answer: you can walk into any room, glance at the detector, and know the CO concentration in real time. An alarm-only detector gives you nothing until a dangerous threshold has already been sustained.

• Plug in a CO detector with a live PPM display as soon as you suspect a problem
• A reading of 0–9 ppm is normal; 10–35 ppm warrants investigation; 35 ppm+ warrants immediate ventilation and evacuation
• If anyone is symptomatic, leave the house first — confirm from outside

AirShield displays live CO, methane, and propane readings simultaneously so you can confirm or rule out a gas problem in seconds — before symptoms have a chance to escalate.